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OpenForecast
(2019)
The development and deployment of new operational runoff forecasting systems are a strong focus of the scientific community due to the crucial importance of reliable and timely runoff predictions for early warnings of floods and flashfloods for local businesses and communities. OpenForecast, the first operational runoff forecasting system in Russia, open for public use, is presented in this study. We developed OpenForecast based only on open-source software and data-GR4J hydrological model, ERA-Interim meteorological reanalysis, and ICON deterministic short-range meteorological forecasts. Daily forecasts were generated for two basins in the European part of Russia. Simulation results showed a limited efficiency in reproducing the spring flood of 2019. Although the simulations managed to capture the timing of flood peaks, they failed in estimating flood volume. However, further implementation of the parsimonious data assimilation technique significantly alleviates simulation errors. The revealed limitations of the proposed operational runoff forecasting system provided a foundation to outline its further development and improvement.
OpenForecast
(2019)
The development and deployment of new operational runoff forecasting systems are a strong focus of the scientific community due to the crucial importance of reliable and timely runoff predictions for early warnings of floods and flashfloods for local businesses and communities. OpenForecast, the first operational runoff forecasting system in Russia, open for public use, is presented in this study. We developed OpenForecast based only on open-source software and data-GR4J hydrological model, ERA-Interim meteorological reanalysis, and ICON deterministic short-range meteorological forecasts. Daily forecasts were generated for two basins in the European part of Russia. Simulation results showed a limited efficiency in reproducing the spring flood of 2019. Although the simulations managed to capture the timing of flood peaks, they failed in estimating flood volume. However, further implementation of the parsimonious data assimilation technique significantly alleviates simulation errors. The revealed limitations of the proposed operational runoff forecasting system provided a foundation to outline its further development and improvement.
Several mechanisms are proposed to be part of the earthquake triggering process, including static stress interactions and dynamic stress transfer. Significant differences of these mechanisms are particularly expected in the spatial distribution of aftershocks. However, testing the different hypotheses is challenging because it requires the consideration of the large uncertainties involved in stress calculations as well as the appropriate consideration of secondary aftershock triggering which is related to stress changes induced by smaller pre- and aftershocks. In order to evaluate the forecast capability of different mechanisms, I take the effect of smaller--magnitude earthquakes into account by using the epidemic type aftershock sequence (ETAS) model where the spatial probability distribution of direct aftershocks, if available, is correlated to alternative source information and mechanisms. Surface shaking, rupture geometry, and slip distributions are tested. As an approximation of the shaking level, ShakeMaps are used which are available in near real-time after a mainshock and thus could be used for first-order forecasts of the spatial aftershock distribution. Alternatively, the use of empirical decay laws related to minimum fault distance is tested and Coulomb stress change calculations based on published and random slip models. For comparison, the likelihood values of the different model combinations are analyzed in the case of several well-known aftershock sequences (1992 Landers, 1999 Hector Mine, 2004 Parkfield). The tests show that the fault geometry is the most valuable information for improving aftershock forecasts. Furthermore, they reveal that static stress maps can additionally improve the forecasts of off--fault aftershock locations, while the integration of ground shaking data could not upgrade the results significantly. In the second part of this work, I focused on a procedure to test the information content of inverted slip models. This allows to quantify the information gain if this kind of data is included in aftershock forecasts. For this purpose, the ETAS model based on static stress changes, which is introduced in part one, is applied. The forecast ability of the models is systematically tested for several earthquake sequences and compared to models using random slip distributions. The influence of subfault resolution and segment strike and dip is tested. Some of the tested slip models perform very good, in that cases almost no random slip models are found to perform better. Contrastingly, for some of the published slip models, almost all random slip models perform better than the published slip model. Choosing a different subfault resolution hardly influences the result, as long the general slip pattern is still reproducible. Whereas different strike and dip values strongly influence the results depending on the standard deviation chosen, which is applied in the process of randomly selecting the strike and dip values.
We present observations from a continuous exposure of an ancient plate interface in the depth range of its former seismogenic zone in the central Alps of Europe related to Late Cretaceous-early Tertiary subduction and accretion of the South Penninic lower plate underneath the Adriatic upper plate. The material forming the exposed plate interface zone has experienced flow and fracturing over an extended period of time followed by syncollisional exhumation, thus reflecting a multistage evolution. Fabric formation and metamorphism, however, chiefly record the deformation conditions of the precollisional setting along the plate interface. We identify an unstable slip domain from pseudotachylytes occurring in the temperature range between 200 and 300 degrees C. This zone coincides with a domain of intense veining in the subduction melange with mineral growth into open cavities, indicating fast, possibly seismic, rupture. Evidence for transient near-lithostatic fluid pressure as well as brittle fractures competing with mylonitic shear zones continues into the region below the occurrence of pseudotachylytes, possibly reflecting a zone of conditionally stable slip. The zone above the unstable slip area is devoid of veins but displays ample evidence of fluid-assisted processes similar to the deeper zone: solution-precipitation creep and dehydration reactions in the melange matrix, hydration, and sealing of the base of the upper plate. Seismic rupture here is possibly expressed by ubiquitous localized deformation zones. We hypothesize that trenchward sealing of parts of the plate interface as well as reaction-enhanced destruction of upper plate permeability is an important component, localizing the unstable slip zone. This relation may result from the competition of the pervasive, presumably interseismic, pressure solution creep destroying permeability and building elevated fluid pressure until the strength threshold is reached with seismic failure.
The Frolikha Fan : a large Pleistocene glaciolacustrine outwash fan in northern Lake Baikal, Siberia
(1998)
This thesis work describes a new experimental method for the determination of Mode II (shear) fracture toughness, KIIC of rock and compares the outcome to results from Mode I (tensile) fracture toughness, KIC, testing using the International Society of Rock Mechanics Chevron-Bend method.Critical Mode I fracture growth at ambient conditions was studied by carrying out a series of experiments on a sandstone at different loading rates. The mechanical and microstructural data show that time- and loading rate dependent crack growth occurs in the test material at constant energy requirement.The newly developed set-up for determination of the Mode II fracture toughness is called the Punch-Through Shear test. Notches were drilled to the end surfaces of core samples. An axial load punches down the central cylinder introducing a shear load in the remaining rock bridge. To the mantle of the cores a confining pressure may be applied. The application of confining pressure favours the growth of Mode II fractures as large pressures suppress the growth of tensile cracks.Variation of geometrical parameters leads to an optimisation of the PTS- geometry. Increase of normal load on the shear zone increases KIIC bi-linear. High slope is observed at low confining pressures; at pressures above 30 MPa low slope increase is evident. The maximum confining pressure applied is 70 MPa. The evolution of fracturing and its change with confining pressure is described.The existence of Mode II fracture in rock is a matter of debate in the literature. Comparison of the results from Mode I and Mode II testing, mainly regarding the resulting fracture pattern, and correlation analysis of KIC and KIIC to physico-mechanical parameters emphasised the differences between the response of rock to Mode I and Mode II loading. On the microscale, neither the fractures resulting from Mode I the Mode II loading are pure mode fractures. On macroscopic scale, Mode I and Mode II do exist.
Here, we study the 3-D subduction initiation process induced by the interaction between a hot thermochemical mantle plume and oceanic lithosphere using thermo-mechanical viscoplastic finite difference marker-in-cell models. Our numerical modeling results show that self-sustaining subduction is induced by plume-lithosphere interaction when the plume is sufficiently buoyant, the oceanic lithosphere is sufficiently old and the plate is weak enough to allow the buoyant plume to. pass through it. Subduction initiation occurs following penetration of the lithosphere by the hot plume and the downward displacement of broken, nearly circular segments of lithosphere (proto-slabs) as a result of partially molten plume rocks overriding the proto-slabs. Our experiments show four different deformation regimes in response to plume-lithosphere interaction: a) self-sustaining subduction initiation, in which subduction becomes self-sustaining; b) frozen subduction initiation, in which subduction stops at shallow depths; c) slab break-off, in which the subducting circular slab breaks off soon after formation; and d) plume underplating, in which the plume does not pass through the lithosphere and instead spreads beneath it (i.e., failed subduction initiation). These regimes depend on several parameters, such as the size, composition, and temperature of the plume, the brittle/plastic strength and age of the oceanic lithosphere, and the presence/absence of lithospheric heterogeneities. The results show that subduction initiates and becomes self-sustaining when the lithosphere is older than 10 Myr and the non dimensional ratio of the plume buoyancy force and lithospheric strength above the plume is higher than approximately 2. The outcomes of our numerical experiments are applicable for subduction initiation in the modern and Precambrian Earth and for the origin of plume-related corona structures on Venus. (C) 2016 Elsevier B.V. All rights reserved.
Initiation of subduction following the impingement of a hot buoyant mantle plume is one of the few scenarios that allow breaking the lithosphere and recycling a stagnant lid without requiring any preexisting weak zones. Here, we investigate factors controlling the number and shape of retreating subducting slabs formed by plume-lithosphere interaction. Using 3-D thermomechanical models we show that the deformation regime, which defines formation of single-slab or multi-slab subduction, depends on several parameters such as age of oceanic lithosphere, thickness of the crust and large-scale lithospheric extension rate. Our model results indicate that on present-day Earth multi-slab plume-induced subduction is initiated only if the oceanic lithosphere is relatively young (<30-40 Myr, but >10 Myr), and the crust has a typical thickness of 8 km. In turn, development of single-slab subduction is facilitated by older lithosphere and pre-imposed extensional stresses. In early Earth, plume-lithosphere interaction could have led to formation of either episodic short-lived circular subduction when the oceanic lithosphere was young or to multi-slab subduction when the lithosphere was old.
It has recently been demonstrated that the interaction of a mantle plume with sufficiently old oceanic lithosphere can initiate subduction. However, the existence of large lithospheric heterogeneities, such as a buoyant plateau, in proximity to a rising plume head may potentially hinder the formation of a new subduction zone. Here, we investigate this scenario by means of 3-D numerical thermomechanical modeling. We explore how plume-lithosphere interaction is affected by lithospheric age, relative location of plume head and plateau border, and the strength of the oceanic crust. Our numerical experiments suggest four different geodynamic regimes: (a) oceanic trench formation, (b) circular oceanic-plateau trench formation, (c) plateau trench formation, and (d) no trench formation. We show that regardless of the age and crustal strength of the oceanic lithosphere, subduction can initiate when the plume head is either below the plateau border or at a distance less than the plume radius from the plateau edge. Crustal heterogeneity facilitates subduction initiation of old oceanic lithosphere. High crustal strength hampers the formation of a new subduction zone when the plume head is located below a young lithosphere containing a thick and strong plateau. We suggest that plume-plateau interaction in the western margin of the Caribbean could have resulted in subduction initiation when the plume head impinged onto the oceanic lithosphere close to the border between plateau and oceanic crust.
Mantle Flow as a Trigger for Subduction Initiation: A Missing Element of the Wilson Cycle Concept
(2017)
The classical Wilson Cycle concept, describing repeated opening and closing of ocean basins, hypothesizes spontaneous conversion of passive continental margins into subduction zones. This process, however, is impeded by the high strength of passive margins, and it has never occurred in Cenozoic times. Here using thermomechanical models, we show that additional forcing, provided by mantle flow, which is induced by neighboring subduction zones and midmantle slab remnants, can convert a passive margin into a subduction zone. Models suggest that this is a long-term process, thus explaining the lack of Cenozoic examples. We speculate that new subduction zones may form in the next few tens of millions of years along the Argentine passive margin and the U.S. East Coast. Mantle suction force can similarly trigger subduction initiation along large oceanic fracture zones. We propose that new subduction zones will preferentially originate where subduction zones were active in the past, thus explaining the remarkable colocation of subduction zones during at least the last 400 Myr.
Initiation of subduction following the impingement of a hot buoyant mantle plume is one of the few scenarios that allow breaking the lithosphere and recycling a stagnant lid without requiring any preexisting weak zones. Here, we investigate factors controlling the number and shape of retreating subducting slabs formed by plume-lithosphere interaction. Using 3-D thermomechanical models we show that the deformation regime, which defines formation of single-slab or multi-slab subduction, depends on several parameters such as age of oceanic lithosphere, thickness of the crust and large-scale lithospheric extension rate. Our model results indicate that on present-day Earth multi-slab plume-induced subduction is initiated only if the oceanic lithosphere is relatively young (<30-40 Myr, but >10 Myr), and the crust has a typical thickness of 8 km. In turn, development of single-slab subduction is facilitated by older lithosphere and pre-imposed extensional stresses. In early Earth, plume-lithosphere interaction could have led to formation of either episodic short-lived circular subduction when the oceanic lithosphere was young or to multi-slab subduction when the lithosphere was old.
Pre-existing weakness zones in the lithosphere such as transform faults/fracture zones and extinct mid-oceanic ridges have been suggested to facilitate subduction initiation in an intra-oceanic environment. Here, we propose that the additional forcing coming from the mantle suction flow is required to trigger the conversion of a fracture zone/transform fault into a converging plate boundary. This suction flow can be induced either from the slab remnants of former converging plate boundaries or/and from slabs of neighbouring active subduction zones. Using 2-D coupled thermo-mechanical models, we show that a sufficiently strong mantle flow is able to convert a fracture zone/transform fault into a subduction zone. However, this process is feasible only if the fracture zone/transform fault is very close to the mid-oceanic ridge. Our numerical model results indicate that time of subduction initiation depends on the velocity, domain size and location of mantle suction flow and age of the oceanic plate.
Accretionary orogens are considered major sites of formation of juvenile continental crust. In the central and southern Andes this is contradicted by two observations: siliciclastic fills of Paleozoic basins in the central Andean segment of the accretionary Terra Australis Orogen consist almost exclusively of shales and mature sandstones; and magmatic rocks connected to the Famatinian (Ordovician) and Late Paleozoic magmatic arcs are predominantly felsic and characterized by significant crustal contamination and strongly unradiogenic Nd isotope compositions. Evidence of juvenile crustal additions is scarce. We present laser ablation (LA)-ICPMS U-Pb ages and LA-MC-ICPMS Hf isotope data of detrital zircons from seven Devonian to Permian turbidite sandstones incorporated into a Late Paleozoic accretionary wedge at the western margin of Gondwana in northern Chile. The combination with Nd whole-rock isotope data permits us to trace the evolution of the South American continental crust through several Proterozoic and Paleozoic orogenic cycles. The analyzed detrital zircon spectra reflect all Proterozoic orogenic cycles representing the step-wise evolution of the accretionary SW Amazonia Orogenic System between 2.0 and 0.9 Ga, followed by the Terra Australis Orogen between 0.9 and 0.25 Ga. The zircon populations are characterized by two prominent maxima reflecting input from Sunsas (Grenville) age magmatic rocks (1.2-0.9 Ga) and from the Ordovician to Silurian Famatinian magmatic arc (0.52-0.42 Ga). Grains of Devonian age are scarce or absent from the analyzed zircon populations. The Hf isotopic compositions of selected dated zircons at the time of their crystallization (epsilon Hf-(T); T = 3.3-0.25 Ga) vary between -18 and +11. All sandstones have a significant juvenile component; between 20 and 50% of the zircons from each sedimentary rock have positive epsilon Hf-(T) and can be considered juvenile. The majority of the juvenile grains have Hf-depleted mantle model ages (Hf T-DM) between 1.55 and 0.8 Ga. the time of the Rondonia-San Ignacio and Sunsas orogenic events on the Amazonia craton. The corresponding whole-rock epsilon Nd-(T) values fot these same rocks are between -8 and -3 indicating a mixture of older evolved and juvenile sources. Nd-depleted mantle model ages (Nd T-DM*) are between 1.5 and 1.2 Ga and coincide broadly with the zircon Hf model ages. Our data indicate that the Paleo- and Mesoproterozoic SW Amazonia Orogenic System, and the subsequent Neoproterozoic and Paleozoic Terra Australis Orogen in the region of the central and southern Andes, developed following two markedly different patterns of accretionary orogenic crustal evolution. The SW Amazonia Orogenic System developed by southwestward growth over approximately 1.1 Ga through a combination of accretion of juvenile material and crustal recycling typical of the extensional or retreating mode of accretionary orogens. In contrast, the central Andean segment of the Terra Australis Orogen evolved from 0.9 to 0.25 Ga in the compressional or advancing mode in a relatively fixed position without the accretion of oceanic crustal units or large scale input of juvenile material to the orogenic crust. Here, recycling mainly of Mesoproterozoic continental crust has been the dominant process of crustal evolution. (C) 2009 Elsevier B.V. All rights reserved.
The formation of the supercontinent Pangaea during the Permo-Triassic gave rise to an extreme monsoonal climate (often termed 'mega-monsoon') that has been documented by numerous palaeo-records. However, considerable debate exists about the role of orbital forcing in causing humid intervals in an otherwise arid climate. To shed new light on the forcing of monsoonal variability in subtropical Pangaea, this study focuses on sediment facies and colour variability of playa and alluvial fan deposits in an outcrop from the late Carnian (ca 225 Ma) in the southern Germanic Basin, south-western Germany. The sediments were deposited against a background of increasingly arid conditions following the humid Carnian Pluvial Event (ca 234 to 232 Ma). The ca 2 center dot 4 Myr long sedimentary succession studied shows a tripartite long-term evolution, starting with a distal mud-flat facies deposited under arid conditions. This phase was followed by a highly variable playa-lake environment that documents more humid conditions and finally a regression of the playa-lake due to a return of arid conditions. The red-green (a*) and lightness (L*) records show that this long-term variability was overprinted by alternating wet/dry cycles driven by orbital precession and ca 405 kyr eccentricity, without significant influence of obliquity. The absence of obliquity in this record indicates that high-latitude forcing played only a minor role in the southern Germanic Basin during the late Carnian. This is different from the subsequent Norian when high-latitude signals became more pronounced, potentially related to the northward drift of the Germanic Basin. The recurring pattern of pluvial events during the late Triassic demonstrates that orbital forcing, in particular eccentricity, stimulated the occurrence and intensity of wet phases. It also highlights the possibility that the Carnian Pluvial Event, although most likely triggered by enhanced volcanic activity, may also have been modified by an orbital stimulus.
Linking deep seismic profiles with regional-scale gravity inversion is a powerful tool to deduce the architecture of rifted margins and their structural evolution. Here we map upper and lower crustal thicknesses of the northern South China Sea (SCS) margin in order to investigate the occurrence of depth-dependent crustal extension from the proximal to the distal margin. By comparing upper and lower crustal stretching factors, we find that the northern margin of the SCS is segmented in three parts: (1) sedimentary basins where upper crust is stretched more than lower crust, (2) distal margin where lower crust is stretched more than upper crust, (3) mostly proximal margin regions where the two layers have similar stretching factors. Our results suggest that sedimentary basins and distal margin prominently feature depth-dependent extension, however accommodated by different processes. While differential thinning within sedimentary basins appears to be governed by lateral pressure variations inducing lower crustal flow, we suggest the distal margin to be affected by a combination of mantle flow-induced lower crustal shearing and sequential fault activity during crustal hyper-extension.
Antarctic glacier forfields are extreme environments and pioneer sites for ecological succession. The Antarctic continent shows microbial community development as a natural laboratory because of its special environment, geographic isolation and little anthropogenic influence. Increasing temperatures due to global warming lead to enhanced deglaciation processes in cold-affected habitats and new terrain is becoming exposed to soil formation and accessible for microbial colonisation. This study aims to understand the structure and development of glacier forefield bacterial communities, especially how soil parameters impact the microorganisms and how those are adapted to the extreme conditions of the habitat. To this effect, a combination of cultivation experiments, molecular, geophysical and geochemical analysis was applied to examine two glacier forfields of the Larsemann Hills, East Antarctica. Culture-independent molecular tools such as terminal restriction length polymorphism (T-RFLP), clone libraries and quantitative real-time PCR (qPCR) were used to determine bacterial diversity and distribution. Cultivation of yet unknown species was carried out to get insights in the physiology and adaptation of the microorganisms. Adaptation strategies of the microorganisms were studied by determining changes of the cell membrane phospholipid fatty acid (PLFA) inventory of an isolated bacterium in response to temperature and pH fluctuations and by measuring enzyme activity at low temperature in environmental soil samples. The two studied glacier forefields are extreme habitats characterised by low temperatures, low water availability and small oligotrophic nutrient pools and represent sites of different bacterial succession in relation to soil parameters. The investigated sites showed microbial succession at an early step of soil formation near the ice tongue in comparison to closely located but rather older and more developed soil from the forefield. At the early step the succession is influenced by a deglaciation-dependent areal shift of soil parameters followed by a variable and prevalently depth-related distribution of the soil parameters that is driven by the extreme Antarctic conditions. The dominant taxa in the glacier forefields are Actinobacteria, Acidobacteria, Proteobacteria, Bacteroidetes, Cyanobacteria and Chloroflexi. The connection of soil characteristics with bacterial community structure showed that soil parameter and soil formation along the glacier forefield influence the distribution of certain phyla. In the early step of succession the relative undifferentiated bacterial diversity reflects the undifferentiated soil development and has a high potential to shift according to past and present environmental conditions. With progressing development environmental constraints such as water or carbon limitation have a greater influence. Adapting the culturing conditions to the cold and oligotrophic environment, the number of culturable heterotrophic bacteria reached up to 108 colony forming units per gram soil and 148 isolates were obtained. Two new psychrotolerant bacteria, Herbaspirillum psychrotolerans PB1T and Chryseobacterium frigidisoli PB4T, were characterised in detail and described as novel species in the family of Oxalobacteraceae and Flavobacteriaceae, respectively. The isolates are able to grow at low temperatures tolerating temperature fluctuations and they are not specialised to a certain substrate, therefore they are well-adapted to the cold and oligotrophic environment. The adaptation strategies of the microorganisms were analysed in environmental samples and cultures focussing on extracellular enzyme activity at low temperature and PLFA analyses. Extracellular phosphatases (pH 11 and pH 6.5), β-glucosidase, invertase and urease activity were detected in the glacier forefield soils at low temperature (14°C) catalysing the conversion of various compounds providing necessary substrates and may further play a role in the soil formation and total carbon turnover of the habitat. The PLFA analysis of the newly isolated species C. frigidisoli showed that the cold-adapted strain develops different strategies to maintain the cell membrane function under changing environmental conditions by altering the PLFA inventory at different temperatures and pH values. A newly discovered fatty acid, which was not found in any other microorganism so far, significantly increased at decreasing temperature and low pH and thus plays an important role in the adaption of C. frigidisoli. This work gives insights into the diversity, distribution and adaptation mechanisms of microbial communities in oligotrophic cold-affected soils and shows that Antarctic glacier forefields are suitable model systems to study bacterial colonisation in connection to soil formation.
The Younger Dryas event, which began approximately 12,900 years ago, was a period of rapid cooling in the Northern Hemisphere, driven by large-scale reorganizations of patterns of atmospheric and oceanic circulation(1-3). Environmental changes during this period have been documented by both proxy-based reconstructions(3) and model simulations(4), but there is currently no consensus on the exact mechanisms of onset, stabilization or termination of the Younger Dryas(5-8). Here we present high-resolution records from two sediment cores obtained from Lake Krakenes in western Norway and the Nordic seas. Multiple proxies from Lake Krakenes are indicative of rapid alternations between glacial growth and melting during the later Younger Dryas. Meanwhile, reconstructed sea surface temperature and salinity from the Nordic seas show an alternation between sea-ice cover and the influx of warm, salty North Atlantic waters. We suggest that the influx of warm water enabled the westerly wind systems to drift northward, closer to their present-day positions. The winds thus brought relatively warm maritime air to Northern Europe, resulting in rising temperatures and the melting of glaciers. Subsequent input of this fresh meltwater into the ocean spurred the formation of sea ice, which forced the westerly winds back to the south, cooling Northern Europe. We conclude that rapid alternations between these two states immediately preceded the termination of the Younger Dryas and the permanent transition to an interglacial state.
Aiming at the stimulation of intrinsic microbial activity, pulses of pure oxygen or pressurized air were recurrently injected into groundwater polluted with chlorobenzene. To achieve well-controlled conditions and intensive sampling, a large, vertical underground tank was filled with the local unconfined sandy aquifer material. In the course of two individual gas injections, one using pure oxygen and one using pressurized air, the mass transfer of individual gas species between trapped gas phase and groundwater was studied. Field data on the dissolved gas composition in the groundwater were combined with a kinetic model on gas dissolution and transport in porous media. Phase mass transfer of individual gas components caused a temporary enrichment of nitrogen, and to a lower degree of methane, in trapped gas leading to the formation of excess dissolved nitrogen levels downgradient from the dissolving gas phase. By applying a novel gas sampling method for dissolved gases in groundwater it was shown that dissolved nitrogen can be used as a partitioning tracer to indicate complete gas dissolution in porous media.
Thirteen N-butylpyridinium salts, including three monometallic [C4Py](2)[MCl4], nine bimetallic [C4Py](2)[(M1-xMxCl4)-M-a-Cl-b] and one trimetallic compound [C4Py](2)[(M1-y-zMyMz (c) Cl4)-M-a-M-b] (M=Co, Cu, Mn; x=0.25, 0.50 or 0.75 and y=z=0.33), were synthesized and their structure and thermal and electrochemical properties were studied. All compounds are ionic liquids (ILs) with melting points between 69 and 93 degrees C. X-ray diffraction proves that all ILs are isostructural. The conductivity at room temperature is between 10(-4) and 10(-8) S cm(-1). Some Cu-based ILs reach conductivities of 10(-2) S cm(-1), which is, however, probably due to IL dec. This correlates with the optical bandgap measurements indicating the formation of large bandgap semiconductors. At elevated temperatures approaching the melting points, the conductivities reach up to 1.47x10(-1) S cm(-1) at 70 degrees C. The electrochemical stability windows of the ILs are between 2.5 and 3.0 V.
Fifteen N-butylpyridinium salts - five monometallic [C4Py](2)[MBr4] and ten bimetallic [C4Py](2)[(M0.5M0.5Br4)-M-a-Br-b] (M=Co, Cu, Mn, Ni, Zn) - were synthesized, and their structures and thermal and electrochemical properties were studied. All the compounds are ionic liquids (ILs) with melting points between 64 and 101 degrees C. Powder and single-crystal X-ray diffraction show that all ILs are isostructural. The electrochemical stability windows of the ILs are between 2 and 3 V. The conductivities at room temperature are between 10(-5) and 10(-6) S cm(-1). At elevated temperatures, the conductivities reach up to 10(-4) S cm(-1) at 70 degrees C. The structures and properties of the current bromide-based ILs were also compared with those of previous examples using chloride ligands, which illustrated differences and similarities between the two groups of ILs.
Foreland-basin systems are excellent archives to decipher the feedbacks between surface and tectonic processes in orogens. The sedimentary architecture of a foreland-basin system reflects the balance between tectonic subsidence causing long-term accommodation space and sediment influx corresponding to efficiency of erosion and mass-redistribution processes. In order to explore the effects of climatic and tectonic forcing in such a system, I investigated the Oligo-Miocene foreland-basin sediments of the southern Alborz mountains, an intracontinental orogen in northern Iran, related to the Arabia-Eurasia continental collision. This work includes absolute dating methods such as 40Ar/39Ar and zircon (U-Th)/He thermochronology, magnetostratigraphy, sedimentological analysis, sandstone and conglomerate provenance study, carbon and oxygen isotope analysis, and clay mineralogy study. Results show a systematic correlation between coarsening-upward cycles and sediment accumulation rates in the basin on 105 to 106yr time scales. During thrust loading phases, the coarse-grained fraction supplied by the uplifting range is stored in the proximal part of the basin (sedimentary facies retrogradation), while fine-grained sediments are deposited in distal sectors. Variations in sediment provenance during these phases of enhanced tectonic activity give evidence for erosional unroofing phases and/or drainage-reorganization events. In addition, enhanced tectonic activity promoted the growth of topography and associated orographic barrier effects, as demonstrated by sedimentologic indicators and the analysis of stable C and O isotopes from calcareous paleosols and lacustrine/palustrine samples. Extensive progradation of coarse-grained deposits occurs during phases of decreased subsidence, when the coarse-grained fraction supplied by the uplifting range cannot be completely stored in the proximal part of the basin. In this environment, a reduction in basin subsidence is associated with laterally stacked fluvial channel deposits, and is related to intra-foreland uplift, as documented by growth strata, tectonic tilting, and sediment reworking. Increase in sediment accumulation rate associated with progradation of vertically-stacked coarse-grained fluvial channels also occurs. Paleosol O-isotope data shows that this increase is related to wetter climatic phases, suggesting that surface processes are more efficient and exhumation rates increase, giving rise to a positive feedback. Furthermore, isotopic and sedimentologic data show that starting from 10-9 Ma, climate became less arid with an increase in seasonality of precipitation. Because important changes were also recorded in the Mediterranean Sea and Asia at that time, the evidence for climatic variability observed in the Alborz mountains most likely reflects changes in Northern Hemisphere atmospheric circulation patterns. This study has additional implications for the evolution of the Alborz mountains and the Arabia-Eurasia continental collision zone. At the orogenic scale, the locus of deformation did not move steadily southward, but stepped forward and backward since Oligocene time. In particular, from ~ 17.5 to 6.2 Ma the orogen grew by a combination of frontal accretion and wedge-internal deformation on time scales of ca. 0.7 to 2 m.y. Moreover, the provenance data suggest that prior to 10-9 Ma the shortening direction changed from NW-SE to NNE-SSW, in agreement with structural data. On the scale of the entire collision zone, the evolution of the studied basins and adjacent mountain ranges suggests a new geodynamic model for the evolution of the Arabia-Eurasia continental collision zone. Numerous sedimentary basins in the Alborz mountains and in other locations of the Arabia-Eurasia collision zone record a change from a tensional (transtensional) to a compressional (transpressional) tectonic setting by ~ 36 Ma. I interpret this to reflect the onset of subduction of the stretched Arabian continental lithosphere beneath central Iran, leading to moderate plate coupling and lower- and upper-plate deformation (soft continental collision). The increase in deformation rates in the southern Alborz mountains from ~ 17.5 Ma suggests that significant upper-plate deformation must have started by the early Miocene most likely in response to an increase in degree of plate coupling. I suggest that this was related to the subduction of thicker Arabian continental lithosphere and the consequent onset of hard continental collision. This model reconciles the apparent lag time of 15-20 m.y between the late Eocene to early Oligocene age for the initial Arabia-Eurasia continental collision and the onset of widespread deformation across the collision zone to the north in early to late Miocene time.
The removal, redistribution, and transient storage of sediments in tectonically active mountain belts is thought to exert a first-order control on shallow crustal stresses, fault activity, and hence on the spatiotemporal pattern of regional deformation processes. Accordingly, sediment loading and unloading cycles in intermontane sedimentary basins may inhibit or promote intrabasinal faulting, respectively, but unambiguous evidence for this potential link has been elusive so far. Here we combine 2D numerical experiments that simulate contractional deformation in a broken-foreland setting (i.e., a foreland where shortening is diachronously absorbed by spatially disparate, reverse faults uplifting basement blocks) with field data from intermontane basins in the NW Argentine Andes. Our modeling results suggest that thicker sedimentary fills (>0.7-1.0 km) may suppress basinal faulting processes, while thinner fills (<0.7 km) tend to delay faulting. Conversely, the removal of sedimentary loads via fluvial incision and basin excavation promotes renewed intrabasinal faulting. These results help to better understand the tectono-sedimentary history of intermontane basins that straddle the eastern border of the Andean Plateau in northwestern Argentina. For example, the Santa Maria and the Humahuaca basins record intrabasinal deformation during or after sediment unloading, while the Quebrada del Toro Basin reflects the suppression of intrabasinal faulting due to loading by coarse conglomerates. We conclude that sedimentary loading and unloading cycles may exert a fundamental control on spatiotemporal deformation patterns in intermontane basins of tectonically active broken forelands. (C) 2018 Elsevier B.V. All rights reserved.
Sedimentary basins in the interior of orogenic plateaus can provide unique insights into the early history of plateau evolution and related geodynamic processes. The northern sectors of the Iranian Plateau of the Arabia-Eurasia collision zone offer the unique possibility to study middle-late Miocene terrestrial clastic and volcaniclastic sediments that allow assessing the nascent stages of collisional plateau formation. In particular, these sedimentary archives allow investigating several debated and poorly understood issues associated with the long-term evolution of the Iranian Plateau, including the regional spatio-temporal characteristics of sedimentation and deformation and the mechanisms of plateau growth. We document that middle-late Miocene crustal shortening and thickening processes led to the growth of a basement-cored range (Takab Range Complex) in the interior of the plateau. This triggered the development of a foreland-basin (Great Pari Basin) to the east between 16.5 and 10.7Ma. By 10.7Ma, a fast progradation of conglomerates over the foreland strata occurred, most likely during a decrease in flexural subsidence triggered by rock uplift along an intraforeland basement-cored range (Mahneshan Range Complex). This was in turn followed by the final incorporation of the foreland deposits into the orogenic system and ensuing compartmentalization of the formerly contiguous foreland into several intermontane basins. Overall, our data suggest that shortening and thickening processes led to the outward and vertical growth of the northern sectors of the Iranian Plateau starting from the middle Miocene. This implies that mantle-flow processes may have had a limited contribution toward building the Iranian Plateau in NW Iran.
This study concerns the Quantitative Phase Analysis (QPA) of historical bricks coming from the complex of the Great Palace of the Byzantine Emperors in Istanbul. The studied samples are characterised by different chemical compositions (low and high calcium content), variable firing temperatures and different amounts of soluble salts as damage products. In the low-Ca samples, the decrease of the phyllosilicate content (from 23.4 to 6.9 wt%) is associated to the increase of the amorphous fraction (from 24 to 48%). This clear negative correlation between the phyllosilicate content and the amorphous fraction indicates that in low-Ca systems vitrification processes are overwhelming with respect to nucleation and recrystallisation processes. By contrast, high-Ca samples present newly formed Ca(Mg) silicates (diopside from 5.7 to 27.2%; anorthite from 1.4 to 8.7%) and aluminium silicates (gehlenite only in two samples, 6.2 and 7.7%) associated to the decrease of quartz (from 27.7 to 11.5%), phyllosilicate (from 6.5% until complete break down) and amorphous (from 30 to 14%) phase fractions. These findings support the role played by the CaO(MgO) content deriving from carbonates decomposition which reacts with Al2O3 and SiO2 oxides from dehydroxylated clay minerals and quartz grains. The above results have been obtained by X-ray powder diffraction data using the combined Rietveld refinement - internal standard method in order to estimate both the crystalline and the amorphous phase fractions. In addition, the coexistence of two distinct plagioclases in high-Ca samples was modelled as follows: a primary albite, which tends to incorporate Ca during the firing process as demonstrated by the increasing of gamma crystallographic angle, and a newly formed anorthite. Finally, by difference between the X-ray fluorescence data and the chemical compositions inferred by QPA, it proved possible to roughly estimate the residual chemical composition attributable to the amorphous fraction. On the basis of our data, we believe that Rietveld refinement combined with the internal standard method represent a powerful tool to better characterise complex polycrystalline and amorphous mixture as in the case of historical bricks
The idea that climatically modulated erosion may impact orogenic processes has challenged geoscientists for decades. Although modeling studies and physical calculations have provided a solid theoretical basis supporting this interaction, to date, field-based work has produced inconclusive results. The central-western Alborz Mountains in the northern sectors of the Arabia-Eurasia collision zone constitute a promising area to explore these potential feedbacks. This region is characterized by asymmetric precipitation superimposed on an orogen with a history of spatiotemporal changes in exhumation rates, deformation patterns, and prolonged, km-scale base-level changes. Our analysis suggests that despite the existence of a strong climatic gradient at least since 17.5 Ma, the early orogenic evolution (from similar to 36 to 9-6 Ma) was characterized by decoupled orographic precipitation and tectonics. In particular, faster exhumation and sedimentation along the more arid southern orogenic flank point to a north-directed accretionary flux and underthrusting of Central Iran. Conversely, from 6 to 3 Ma, erosion rates along the northern orogenic flank became higher than those in the south, where they dropped to minimum values. This change occurred during a similar to 3-Myr-long, km-scale base-level lowering event in the Caspian Sea. We speculate that mass redistribution processes along the northern flank of the Alborz and presumably across all mountain belts adjacent to the South Caspian Basin and more stable areas of the Eurasian plate increased the sediment load in the basin and ultimately led to the underthrusting of the Caspian Basin beneath the Alborz Mountains. This underthrusting in turn triggered a new phase of northward orogenic expansion, transformed the wetter northern flank into a new pro-wedge, and led to the establishment of apparent steady-state conditions along the northern orogenic flank (i.e., rock uplift equal to erosion rates). Conversely, the southern mountain front became the retro-wedge and experienced limited tectonic activity. These observations overall raise the possibility that mass-distribution processes during a pronounced erosion phase driven by base-level changes may have contributed to the inferred regional plate-tectonic reorganization of the northern Arabia-Eurasia collision during the last similar to 5 Ma. (C) 2015 Elsevier B.V. All rights reserved.
The Central Pontides of N Turkey represents a mobile orogenic belt of the southern Eurasian margin that experienced several phases of exhumation associated with the consumption of different branches of the Neo-Tethys Ocean and the amalgamation of continental domains. Our new low-temperature thermochronology data help to constrain the timing of these episodes, providing new insights into associated geodynamic processes. In particular, our data suggest that exhumation occurred at (1) similar to 110 to 90Ma, most likely during tectonic accretion and exhumation of metamorphic rocks from the subduction zone; (2) from similar to 60 to 40Ma, during the collision of the Kirehir and Anatolide-Tauride microcontinental domains with the Eurasian margin; (3) from similar to 0 to 25Ma, either during the early stages of the Arabia-Eurasia collision (soft collision) when the Arabian passive margin reached the trench, implying 70 to 530km of subduction of the Arabian passive margin, or during a phase of trench advance predating hard collision at similar to 20Ma; and (4) similar to 11Ma to the present, during transpression associated with the westward motion of Anatolia. Our findings document the punctuated nature of fault-related exhumation, with episodes of fast cooling followed by periods of slow cooling or subsidence, the role of inverted normal faults in controlling the Paleogene exhumation pattern, and of the North Anatolian Fault in dictating the most recent pattern of exhumation.
The southern foreland basin of the Alborz Mountains of northern Iran is characterized by an approximately 7.3-km-thick sequence of Miocene sedimentary rocks, constituting three basin-wde coarsening-upward units spanning a period of 10(6)years. We assess available magnetostratigraphy, paleoclimatic reconstructions, stratal architecture, records of depositional environments, and sediment-provenance data to characterize the relationships between tectonically-generated accommodation space (A) and sediment supply (S). Our analysis allows an inversion of the stratigraphy for particular forcing mechanisms, documenting causal relationships, and providing a basis to decipher the relative contributions of tectonics and climate (inferred changes in precipitation) in controlling sediment supply to the foreland basin. Specifically, A/S>1, typical of each basal unit (17.5-16.0, 13.8-13.1 and 10.3-9.6Ma), is associated with sharp facies retrogradation and reflects substantial tectonic subsidence. Within these time intervals, arid climatic conditions, changes in sediment provenance, and accelerated exhumation in the orogen suggest that sediment supply was most likely driven by high uplift rates. Conversely, A/S<1 (13.8 and 13.8-11Ma, units 1, and 2) reflects facies progradation during a sharp decline in tectonic subsidence caused by localized intra-basinal uplift. During these time intervals, climate continued to be arid and exhumation active, suggesting that sediment supply was again controlled by tectonics. A/S<1, at 11-10.3Ma and 9-6-7.6Ma (and possibly 6.2; top of units 2 and 3), is also associated with two episodes of extensive progradation, but during wetter phases. The first episode appears to have been linked to a pulse in sediment supply driven by an increase in precipitation. The second episode reflects a balance between a climatically-induced increase in sediment supply and a reduction of subsidence through the incorporation of the proximal foreland into the orogenic wedge. This in turn caused an expansion of the catchment and a consequent further increase in sediment supply.
A poorly understood lag time of 15-20 m.y. exists between the initial Arabia-Eurasia continental collision in late Eocene to early Oligocene time and the acceleration of tectonic and sedimentary processes across the collision zone in the early to late Miocene. The late Eocene to Miocene-Pliocene clastic and shallow-marine sedimentary rocks of the Kond, Eyvanekey, and Semnan Basins in the Alborz Mountains (northern Iran) offer the possibility to track the evolution of this orogen in the framework of collision processes. A transition from volcaniclastic submarine deposits to shallow-marine evaporites and terrestrial sediments occurred shortly after 36 Ma in association with reversals in sediment provenance, strata tilting, and erosional unroofing. These events followed the termination of subduction arc magmatism and marked a changeover from an extensional to a contractional regime in response to initiation of continental collision with the subduction of stretched Arabian lithosphere. This early stage of collision produced topographic relief associated with shallow foreland basins, suggesting that shortening and tectonic loading occurred at low rates. Starting from the early Miocene (17.5 Ma), flexural subsidence in response to foreland basin initiation occurred. Fast sediment accumulation rates and erosional unroofing trends point to acceleration of shortening by the early Miocene. We suggest that the lag time between the initiation of continental collision (36 Ma) and the acceleration of regional deformation (20-17.5 Ma) reflects a two-stage collision process, involving the "soft" collision of stretched lithosphere at first and "hard" collision following the arrival of unstretched Arabian continental litho sphere in the subduction zone.
With this paper, we assess the present-day conductive thermal field of the Glueckstadt Graben in NW Germany that is characterized by large salt walls and diapirs structuring the graben fill. We use a finite element method to calculate the 3D steady-state conductive thermal field based on a lithosphere-scale 3D structural model that resolves the first-order structural characteristics of the graben and its underlying lithosphere. Model predictions are validated against measured temperatures in six deep wells. Our investigations show that the interaction of thickness distributions and thermal rock properties of the different geological layers is of major importance for the distribution of temperatures in the deep subsurface of the Glueckstadt Graben. However, the local temperatures may result from the superposed effects of different controlling factors. Especially, the upper sedimentary part of the model exhibits huge lateral temperature variations, which correlate spatially with the shape of the thermally highly conductive Permian salt layer. Variations in thickness and geometry of the salt cause two major effects, which provoke considerable lateral temperature variations for a given depth. (1) The "chimney effect" causes more efficient heat transport within salt diapirs. As a consequence positive thermal anomalies develop in the upper part and above salt structures, where the latter are covered by much less conductive sediments. In contrast, negative thermal anomalies are noticeable underneath salt structures. (2) The "thermal blanketing effect" is caused by thermally low conductive sediments that provoke the local storage of heat where these insulating sediments are present. The latter effect leads to both local and regional thermal anomalies. Locally, this translates to higher temperatures where salt margin synclines are filled with thick insulating clastic sediments. For the regional anomalies the cumulative insulating effects of the entire sediment fill results in a long-wavelength variation of temperatures in response to heat refraction effects caused by the contrast between insulating sediments and highly conductive crystalline crust. Finally, the longest wavelength of temperature variations is caused by the depth position of the isothermal lithosphere-asthenosphere boundary defining the regional variations of the overall geothermal gradient. We find that a conductive thermal model predicts observed temperatures reasonably well for five of the six available wells, whereas the steady-state conductive approach appears not to be valid for the sixth well.
Intracontinental deformation usually is a result of tectonic forces associated with distant plate collisions. In general, the evolution of mountain ranges and basins in this environment is strongly controlled by the distribution and geometries of preexisting structures. Thus, predictive models usually fail in forecasting the deformation evolution in these kinds of settings. Detailed information on each range and basin-fill is vital to comprehend the evolution of intracontinental mountain belts and basins. In this dissertation, I have investigated the complex Cenozoic tectonic evolution of the western Tien Shan in Central Asia, which is one of the most active intracontinental ranges in the world. The work presented here combines a broad array of datasets, including thermo- and geochronology, paleoenvironmental interpretations, sediment provenance and subsurface interpretations in order to track changes in tectonic deformation. Most of the identified changes are connected and can be related to regional-scale processes that governed the evolution of the western Tien Shan.
The NW-SE trending Talas-Fergana fault (TFF) separates the western from the central Tien Shan and constitutes a world-class example of the influence of preexisting anisotropies on the subsequent structural development of a contractile orogen. While to the east most of ranges and basins have a sub-parallel E-W trend, the triangular-shaped Fergana basin forms a substantial feature in the western Tien Shan morphology with ranges on all three sides. In this thesis, I present 55 new thermochronologic ages (apatite fission track and zircon (U-Th)/He)) used to constrain exhumation histories of several mountain ranges in the western Tien Shan. At the same time, I analyzed the Fergana basin-fill looking for progressive changes in sedimentary paleoenvironments, source areas and stratal geometrical configurations in the subsurface and outcrops.
The data presented in this thesis suggests that low cooling rates (<1°C Myr-1), calm depositional environments, and low depositional rates (<10 m Myr-1) were widely distributed across the western Tien Shan, describing a quiescent tectonic period throughout the Paleogene. Increased cooling rates in the late Cenozoic occurred diachronously and with variable magnitudes in different ranges. This rapid cooling stage is interpreted to represent increased erosion caused by active deformation and constrains the onset of Cenozoic deformation in the western Tien Shan. Time-temperature histories derived from the northwestern Tien Shan samples show an increase in cooling rates by ~25 Ma. This event is correlated with a synchronous pulse
iv
in the South Tien Shan. I suggest that strike-slip motion along the TFF commenced at the Oligo-Miocene boundary, facilitating CCW rotation of the Fergana basin and enabling exhumation of the linked horsetail splays. Higher depositional rates (~150 m Myr-1) in the Oligo-Miocene section (Massaget Fm.) of the Fergana basin suggest synchronous deformation in the surrounding ranges. The central Alai Range also experienced rapid cooling around this time, suggesting that the onset of intramontane basin fragmentation and isolation is coeval. These results point to deformation starting simultaneously in the late Oligocene – early Miocene in geographically distant mountain ranges. I suggest that these early uplifts are controlled by reactivated structures (like the TFF), which are probably the frictionally weakest and most-suitably oriented for accommodating and transferring N-S horizontal shortening along the western Tien Shan.
Afterwards, in the late Miocene (~10 Ma), a period of renewed rapid cooling affected the Tien Shan and most mountain ranges and inherited structures started to actively deform. This episode is widely distributed and an increase in exhumation is interpreted in most of the sampled ranges. Moreover, the Pliocene section in the basin subsurface shows the higher depositional rates (>180 m Myr-1) and higher energy facies. The deformation and exhumation increase further contributed to intramontane basin partitioning. Overall, the interpretation is that the Tien Shan and much of Central Asia suffered a global increase in the rate of horizontal crustal shortening. Previously, stress transfer along the rigid Tarim block or Pamir indentation has been proposed to account for Himalayan hinterland deformation. However, the extent of the episode requires a different and broader geodynamic driver.
Sedimentological, provenance, and detrital thermochronological results for basin fill at the modern deformation front of the northern Andes (6 degrees N latitude) provide a long-term, Eocene to Pliocene record of foreland-basin sedimentation along the Eastern Cordillera !Janos basin boundary in Colombia. Lithofacies assemblages and paleocurrent orientations in the upward-coarsening, 5-km-thick succession of the Nunchia syncline reveal a systematic shift from craton-derived, shallow-marine distal foreland (back-bulge) accumulation in the Mirador Formation, to orogen-sourced, deltaic, and coastalinfluenced sedimentation of the distal to medial foreland (foredeep) in the Carbonera and Leon Formations, to anastomosing fluvial and distributive braided fluvial megafan systems of the proximal foreland (foredeep to wedge-top) basin in the lower and upper Guayabo Formation. These changes in depositional processes and sediment dispersal are supported by up-section variations in detrital zircon U-Pb and (U-Th)/He ages that record exhumation of evolving, compartmentalized sediment source areas in the Eastern Cordillera. The data are interpreted in terms of a progressive eastward advance in foldand-thrust deformation, with late Eocene Oligocene deformation in the axial zone of the Eastern Cordillera along the western edge of Floresta basin (Soapaga thrust), early Miocene reactivation (inversion) of the eastern margin of the Mesozoic rift system (Pajarito and Guaicaramo thrusts), and middle late Miocene propagation of a footwall shortcut fault (Vopal thrust) that created the Nunchia syncline in a wedge-top (piggyback) setting of the eastern foothills along the transition from the Eastern Cordillera to Harms foreland basin. Collectively, the data presented here for the frontal Eastern Cordillera define a general in-sequence pattern of eastwardadvancing fold-and-thrust deformation during Cenozoic east-west shortening in the Colombian Andes.
The origins and development of the arid and highly seasonal steppe-desert biome in Central Asia, the largest of its kind in the world, remain largely unconstrained by existing records. It is unclear how Cenozoic climatic, geological, and biological forces, acting at diverse spatial and temporal scales, shaped Central Asian ecosystems through time. Our synthesis shows that the Central Asian steppe-desert has existed since at least Eocene times but experienced no less than two regime shifts, one at the Eocene-Oligocene Transition and one in the mid-Miocene. These shifts separated three successive "stable states," each characterized by unique floral and faunal structures. Past responses to disturbance in the Asian steppe-desert imply that modern ecosystems are unlikely to recover their present structures and diversity if forced into a new regime. This is of concern for Asian steppes today, which are being modified for human use and lost to desertification at unprecedented rates.
Groundwater recharge (GWR) is one of the most challenging water fluxes to estimate, as it relies on observed data that are often limited in many developing countries.
This study developed an innovative water budget method using satellite products for estimating the spatially distributed GWR at monthly and annual scales in tropical wet sedimentary regions despite cloudy conditions.
The distinctive features proposed in this study include the capacity to address 1) evapotranspiration estimations in tropical wet regions frequently overlaid by substantial cloud cover; and 2) seasonal root-zone water storage estimations in sedimentary regions prone to monthly variations.
The method also utilises satellite-based information of the precipitation and surface runoff. The GWR was estimated and validated for the hydrologically contrasting years 2016 and 2017 over a tropical wet sedimentary region located in North-eastern Brazil, which has substantial potential for groundwater abstraction.
This study showed that applying a cloud-cleaning procedure based on monthly compositions of biophysical data enables the production of a reasonable proxy for evapotranspiration able to estimate groundwater by the water budget method.
The resulting GWR rates were 219 (2016) and 302 (2017) mm yr(-1), showing good correlations (CC = 0.68 to 0.83) and slight underestimations (PBIAS =-13 to-9%) when compared with the referenced estimates obtained by the water table fluctuation method for 23 monitoring wells. Sensitivity analysis shows that water storage changes account for +19% to-22% of our monthly evaluation.
The satellite-based approach consistently demonstrated that the consideration of cloud-cleaned evapotranspiration and root-zone soil water storage changes are essential for a proper estimation of spatially distributed GWR in tropical wet sedimentary regions because of their weather seasonality and cloudy conditions.
The lack of process-based classification procedures may lead to unrealistic hyetograph design due to complex oscillation of rainfall depths when assimilated at high temporal resolutions. Four consecutive years of sub-hourly rainfall data were assimilated in three study areas (Guaraira, GEB, Sao Joao do Cariri, CEB, and Aiuaba, AEB) under distinct climates (very hot semi-arid and tropical wet). This study aimed to define rainfall events (for Minimum Inter-event Time, MIT, and Minimum Rainfall Depth, MRD, equal to 30 min and 1.016 mm, respectively), classify their hyetograph types (rectangular, R, unimodal with left-skewed, UL, right-skewed, UR, and centred peaks, UC, bimodal, B, and shapeless, SL), and compare their key rainfall properties (frequency, duration, depth, rate and peak). A rain pulse aggregation process allowed for reshaping SL-events for six different time spans varying from 2 to 30 min. The results revealed that the coastal area held predominantly R-events (64% events and 49% rainfall depth), in western semi-arid prevailed UL-events (57% events and 63% rainfall depth), whereas in eastern semi-arid mostly were R-events (61% events and 30% rainfall depth) similar to coastal area. It is concluded that each cloud formation type had important effects on hyetograph properties, differentiating them even within the same climate.
The Eastern Mediterranean is the most seismically active region in Europe due to the complex interactions of the Arabian, African, and Eurasian tectonic plates. Deformation is achieved by faulting in the brittle crust, distributed flow in the viscoelastic lower-crust and mantle, and Hellenic subduction, but the long-term partitioning of these mechanisms is still unknown. We exploit an extensive suite of geodetic observations to build a kinematic model connecting strike-slip deformation, extension, subduction, and shear localization across Anatolia and the Aegean Sea by mapping the distribution of slip and strain accumulation on major active geological structures. We find that tectonic escape is facilitated by a plate-boundary-like, translithospheric shear zone extending from the Gulf of Evia to the Turkish-Iranian Plateau that underlies the surface trace of the North Anatolian Fault. Additional deformation in Anatolia is taken up by a series of smaller-scale conjugate shear zones that reach the upper mantle, the largest of which is located beneath the East Anatolian Fault. Rapid north-south extension in the western part of the system, driven primarily by Hellenic Trench retreat, is accommodated by rotation and broadening of the North Anatolian mantle shear zone from the Sea of Marmara across the north Aegean Sea, and by a system of distributed transform faults and rifts including the rapidly extending Gulf of Corinth in central Greece and the active grabens of western Turkey. Africa-Eurasia convergence along the Hellenic Arc occurs at a median rate of 49.8mm yr(-1) in a largely trench-normal direction except near eastern Crete where variably oriented slip on the megathrust coincides with mixed-mode and strike-slip deformation in the overlying accretionary wedge near the Ptolemy-Pliny-Strabo trenches. Our kinematic model illustrates the competing roles the North Anatolian mantle shear zone, Hellenic Trench, overlying mantle wedge, and active crustal faults play in accommodating tectonic indentation, slab rollback and associated Aegean extension. Viscoelastic flow in the lower crust and upper mantle dominate the surface velocity field across much of Anatolia and a clear transition to megathrust-related slab pull occurs in western Turkey, the Aegean Sea and Greece. Crustal scale faults and the Hellenic wedge contribute only a minor amount to the large-scale, regional pattern of Eastern Mediterranean interseismic surface deformation.
In Germany, the irrigation sector accounts for only 1% of water use. In recent years, however, this sector has attracted more attention due to the occurrence of severe drought periods. Irrigation scheduling systems could support adaptation strategies but little is known about current providers, performance and users. In this study we aimed to depict the current situation of the existence and functioning of irrigation scheduling systems available in Germany. Six methods were identified and assessed based on direct interviews with end-users and a comparative analysis. The results showed a positive feedback from the users. However, the recommendations were rarely implemented, while only the seasonal irrigation requirement was considered to support actual water abstraction. These results were corroborated by the comparative analysis. Five of the six irrigation scheduling systems estimated the seasonal irrigation amount consistently, while wider differences were found by looking at the irrigation season and at the number of irrigations. Overall, it is found that irrigation support systems are valuable tools for supporting adaptation strategies to fast changes in agro-environmental conditions. However, specific assessments based on real measurements should be considered in order to improve the performance of the systems and provide more consistent support to end-users. (c) 2019 John Wiley & Sons, Ltd.
An effective strategy for combining variance- and distribution-based global sensitivity analysis
(2020)
We present a new strategy for performing global sensitivity analysis capable to estimate main and interaction effects from a generic sampling design. The new strategy is based on a meaningful combination of varianceand distribution-based approaches. The strategy is tested on four analytic functions and on a hydrological model. Results show that the analysis is consistent with the state-of-the-art Saltelli/Jansen formula but to better quantify the interaction effect between the input factors when the output distribution is skewed. Moreover, the estimation of the sensitivity indices is much more robust requiring a smaller number of simulations runs. Specific settings and alternative methods that can be integrated in the new strategy are also discussed. Overall, the strategy is considered as a new simple and effective tool for performing global sensitivity analysis that can be easily integrated in any environmental modelling framework.
Soil moisture dynamics are affected by complex interactions among several factors. Understanding the relative importance of these factors is still an important challenge in the study of water fluxes and solute transport in unsaturated media. In this study, the spatio-temporal variability of surface soil moisture was investigated in a 10 ha flat cropped field located in northern Italy. Soil moisture was measured on a regular 50 x 50 m grid on seven dates during the growing season. For each measurement campaign, the spatial variability of the soil moisture was compared with the spatial variability of the soil texture and crop properties. In particular, to better understand the role of the vegetation, the spatio-temporal variability of two different parameters - leaf area index and crop height - was monitored on eight dates at different crop development stages. Statistical and geostatistical analysis was then applied to explore the interactions between these variables. In agreement with other studies, the results show that the soil moisture variability changes according to the average value within the field, with the standard deviation reaching a maximum value under intermediate mean soil moisture conditions and the coefficient of variation decreasing exponentially with increasing mean soil moisture. The controls of soil moisture variability change according to the average soil moisture within the field. Under wet conditions, the spatial distribution of the soil moisture reflects the variability of the soil texture. Under dry conditions, the spatial distribution of the soil moisture is affected mostly by the spatial variability of the vegetation. The interaction between these two factors is more important under intermediate soil moisture conditions. These results confirm the importance of considering the average soil moisture conditions within a field when investigating the controls affecting the spatial variability of soil moisture. This study highlights the importance of considering the spatio-temporal variability of the vegetation in investigating soil moisture dynamics, especially under intermediate and dry soil moisture conditions. The results of this study have important implications in different hydrological applications, such as for sampling design, ranking stability application, indirect measurements of soil properties and model parameterisation.
Cosmic-Ray neutron sensing (CRS) is a unique approach to measure soil moisture at field scale filling the gap of current methodologies. However, CRS signal is affected by all the hydrogen pools on the land surface and understanding their relative importance plays an important role for the application of the method e.g., validation of remote sensing products and data assimilation. In this study, a soil moisture scaling approach is proposed to estimate directly the correct CRS soil moisture based on the soil moisture profile measured at least in one position within the field. The approach has the advantage to avoid the need to introduce one correction for each hydrogen contribution and to estimate indirectly all the related time-varying hydrogen pools. Based on the data collected in three crop seasons, the scaling approach shows its ability to identify and to quantify the seasonal biomass water equivalent. Additionally, the analysis conducted at sub-daily time resolution is able to quantify the daily vertical redistribution of the water biomass and the rainfall interception, showing promising applications of the CRS method also for these types of measurements. Overall, the study underlines how not only soil moisture but all the specific hydrological processes in the soil-plant-atmosphere continuum should be considered for a proper evaluation of the CRS signal. For this scope, the scaling approach reveals to be a simple and pragmatic analysis that can be easily extended to other experimental sites. (C) 2015 Elsevier B.V. All rights reserved.
Cosmic-ray neutron sensing (CRNS) is a promising proximal soil sensing technique to estimate soil moisture at intermediate scale and high temporal resolution. However, the signal shows complex and non-unique response to all hydrogen pools near the land surface, providing some challenges for soil moisture estimation in practical applications. Aims of the study were 1) to assess the uncertainty of CRNS as a stand-alone approach to estimate volumetric soil moisture in cropped field 2) to identify the causes of this uncertainty 3) and possible improvements. Two experimental sites in Germany were equipped with a CRNS probe and point-scale soil moisture network. Additional monitoring activities were conducted during the crop growing season to characterize the soil-plant systems. This data is used to identify and quantify the different sources of uncertainty (factors). An uncertainty analysis, based on Monte Carlo approach, is applied to propagate these uncertainties to CRNS soil moisture estimations. In addition, a sensitivity analysis based on the Sobol’ method is performed to identify the most important factors explaining this uncertainty. Results show that CRNS soil moisture compares well to the soil moisture network when these point-scale values are weighted to account for the spatial sensitivity of the signal and other sources of hydrogen (lattice water and organic carbon) are added to the water content. However, the performance decreases when CRNS is considered as a stand-alone method to retrieve the actual (non-weighted) volumetric soil moisture. The support volume (penetration depth and radius) shows also a considerable uncertainty, especially in relatively dry soil moisture conditions. Four of the seven factors analyzed (the vertical soil moisture profile, bulk density, incoming neutron correction and the calibrated parameter N0) were found to play an important role. Among the possible improvements identified, a simple correction factor based on vertical point-scale soil moisture profiles shows to be a promising approach to account for the sensitivity of the CRNS signal to the upper soil layers.
The present study proposes a General Probabilistic Framework (GPF) for uncertainty and global sensitivity analysis of deterministic models in which, in addition to scalar inputs, non-scalar and correlated inputs can be considered as well. The analysis is conducted with the variance-based approach of Sobol/Saltelli where first and total sensitivity indices are estimated. The results of the framework can be used in a loop for model improvement, parameter estimation or model simplification. The framework is applied to SWAP, a 113 hydrological model for the transport of water, solutes and heat in unsaturated and saturated soils. The sources of uncertainty are grouped in five main classes: model structure (soil discretization), input (weather data), time-varying (crop) parameters, scalar parameters (soil properties) and observations (measured soil moisture). For each source of uncertainty, different realizations are created based on direct monitoring activities. Uncertainty of evapotranspiration, soil moisture in the root zone and bottom fluxes below the root zone are considered in the analysis. The results show that the sources of uncertainty are different for each output considered and it is necessary to consider multiple output variables for a proper assessment of the model. Improvements on the performance of the model can be achieved reducing the uncertainty in the observations, in the soil parameters and in the weather data. Overall, the study shows the capability of the GPF to quantify the relative contribution of the different sources of uncertainty and to identify the priorities required to improve the performance of the model. The proposed framework can be extended to a wide variety of modelling applications, also when direct measurements of model output are not available.
Soil properties show high heterogeneity at different spatial scales and their correct characterization remains a crucial challenge over large areas. The aim of the study is to quantify the impact of different types of uncertainties that arise from the unresolved soil spatial variability on simulated hydrological states and fluxes. Three perturbation methods are presented for the characterization of uncertainties in soil properties. The methods are applied on the soil map of the upper Neckar catchment (Germany), as an example. The uncertainties are propagated through the distributed mesoscale hydrological model (mHM) to assess the impact on the simulated states and fluxes. The model outputs are analysed by aggregating the results at different spatial and temporal scales. These results show that the impact of the different uncertainties introduced in the original soil map is equivalent when the simulated model outputs are analysed at the model grid resolution (i.e. 500 m). However, several differences are identified by aggregating states and fluxes at different spatial scales (by subcatchments of different sizes or coarsening the grid resolution). Streamflow is only sensitive to the perturbation of long spatial structures while distributed states and fluxes (e.g. soil moisture and groundwater recharge) are only sensitive to the local noise introduced to the original soil properties. A clear identification of the temporal and spatial scale for which finer-resolution soil information is (or is not) relevant is unlikely to be universal. However, the comparison of the impacts on the different hydrological components can be used to prioritize the model improvements in specific applications, either by collecting new measurements or by calibration and data assimilation approaches. In conclusion, the study underlines the importance of a correct characterization of uncertainty in soil properties. With that, soil maps with additional information regarding the unresolved soil spatial variability would provide strong support to hydrological modelling applications.
The Southern Central Andes (33°-36°S) are an excellent natural laboratory to study orogenic deformation processes, where boundary conditions, such as the geometry of the subducted plate, impose an important control on the evolution of the orogen. On the other hand, the South American plate presents a series of heterogeneities that additionally impart control on the mode of deformation. This thesis aims to test the control of this last factor over the construction of the Cenozoic Andean orogenic system.
From the integration of surface and subsurface information in the southern area (34-36°S), the evolution of Andean deformation over the steeply dipping subduction segment was studied. A structural model was developed evaluating the stress state from the Miocene to the present-day and its influence in the migration of magmatic fluids and hydrocarbons. Based on these data, together with the data generated by other researchers in the northern zone of the study area (33-34°S), geodynamic numerical modeling was performed to test the hypothesis of the decisive role of upper-plate heterogeneities in the Andean evolution. Geodynamic codes (LAPEX-2D and ASPECT) which simulate the behavior of materials with elasto-visco-plastic rheologies under deformation, were used. The model results suggest that upper-plate contractional deformation is significantly controlled by the strength of the lithosphere, which is defined by the composition of the upper and lower crust, and by the proportion of lithospheric mantle, which in turn is determined by previous tectonic events. In addition, the previous regional tectono-magmatic events also defined the composition of the crust and its geometry, which is another factor that controls the localization of deformation. Accordingly, with more felsic lower crustal composition, the deformation follows a pure-shear mode, while more mafic compositions induce a simple-shear deformation mode. On the other hand, it was observed that initial lithospheric thickness may fundamentally control the location of deformation, with zones characterized by thin lithosphere are prone to concentrate it. Finally, it was found that an asymmetric lithosphere-astenosphere boundary resulting from corner flow in the mantle wedge of the eastward-directed subduction zone tends to generate east-vergent detachments.
In this paper, we examine the influence of the 27 October 2012, M-w 7.8 earthquake on landslide occurrence in the southern half of Haida Gwaii (formerly Queen Charlotte Islands), British Columbia, Canada. Our 1350 km(2) study area is undisturbed, primarily forested terrain that has not experienced road building or timber harvesting. Our inventory of landslide polygons is based on optical airborne and spaceborne images acquired between 2007 and 2018, from which we extracted and mapped 446 individual landslides (an average of 33 landslides per 100 km(2)). The landslide rate in years without major earthquakes averages 19.4 per year, or 1.4/100 km(2)/year, and the annual average area covered by non-seismically triggered landslides is 35 ha/year. The number of landslides identified in imagery closely following the 2012 earthquake, and probably triggered by it, is 244 or an average of about 18 landslides per 100 km(2). These landslides cover a total area of 461 ha. In the following years-2013-2016 and 2016-2018-the number of landslides fell, respectively, to 26 and 13.5 landslides per year. In non-earthquake years, most landslides happen on south-facing slopes, facing the prevailing winds. In contrast, during or immediately after the earthquake, up to 32% of the landslides occurred on north and northwest-facing slopes. Although we could not find imagery from the day after the earthquake, overview reconnaissance flights 10 and 16 days later showed that most of the landslides were recent, suggesting they were co-seismic.
A hydrochemical approach to quantify the role of return flow in a surface flow-dominated catchment
(2017)
Stormflow generation in headwater catchments dominated by subsurface flow has been studied extensively, yet catchments dominated by surface flow have received less attention. We addressed this by testing whether stormflow chemistry is controlled by either (a) the event-water signature of overland flow, or (b) the pre-event water signature of return flow. We used a high-resolution hydrochemical data set of stormflow and end-members of multiple storms in an end-member mixing analysis to determine the number of end-members needed to explain stormflow, characterize and identify potential end-members, calculate their contributions to stormflow, and develop a conceptual model of stormflow. The arrangement and relative positioning of end-members in stormflow mixing space suggest that saturation excess overland flow (26-48%) and return flow from two different subsurface storage pools (17-53%) are both similarly important for stormflow. These results suggest that pipes and fractures are important flow paths to rapidly release stored water and highlight the value of within-event resolution hydrochemical data to assess the full range and dynamics of flow paths.
End member mixing analysis (EMMA) is a commonly applied method to identify and quantify the dominant runoff producing sources of water. It employs tracers to determine the dimensionality of the hydrologic system. Many EMMA studies have been conducted using two to six tracers, with some of the main tracers being Ca, Na, Cl(-), water isotopes, and alkalinity. Few studies use larger tracer sets including minor trace elements such as Li, Rb, Sr, and Ba. None of the studies has addressed the question of the tracer set size and composition, despite the fact that these determine which and how many end members (EM) will be identified. We examine how tracer set size and composition affects the conceptual model that results from an EMMA. We developed an automatic procedure that conducts EMMA while iteratively changing tracer set size and composition. We used a set of 14 tracers and 9 EMs. The validity of the resulting conceptual models was investigated under the aspects of dimensionality, EM combinations, and contributions to stream water. From the 16,369 possibilities, 23 delivered plausible results. The resulting conceptual models are highly sensitive to the tracer set size and composition. The moderate reproducibility of EM contributions indicates a still missing EM. It also emphasizes that the major elements are not always the most useful tracers and that larger tracer sets have an enhanced capacity to avoid false conclusions about catchment functioning. The presented approach produces results that may not be apparent from the traditional approach and it is a first step to add the idea of statistical significance to the EMMA approach.
The spatial distribution of soil types is controlled by a set of environmental factors such as climate, organisms, parent material and topography as well as time and space. A change of these factors will lead to a change in the spatial distribution of soil types. In this study, we use a digital soil mapping approach to improve our knowledge about major soil type distributing factors in the steppe regions of Inner Mongolia (China) which currently undergo tremendous environmental change, e.g. climate and land use change. We use Random Forests in an effort to map Reference Soil Groups according to the World Reference Base for Soil Resources (WRB) in the Xilin River catchment. We benefit from the superior prediction capabilities of RF and additional interpretive results in order to identify the major environmental factors that control spatial patterns of soil types. The nine WRB soil groups that were identified and spatially predicted for the study area are Arenosol, Calcisol, Cambisol, Chernozem, Cryosol, Gleysol, Kastanozem, Phaeozem and Regosol.
Model and prediction performances of the RF model are high with an Out-of-Bag error of 51.6% for the model and a misclassification error for the predicted map of 28.9%. The main controlling factors of soil type distribution are land use, a set of topographic variables, geology and climate. However, land use and climate are of major importance and topography and geology are of minor importance. The visualizations of the predictions, the variable importance measures as result of RF and the comparisons of these with the spatial distribution of the environmental factors delivered additional, quantitative information of these controlling factors and revealed that intensively grazed areas are subjected to soil degradation. However, most of the area is still governed by natural soil forming processes which are driven by climate, topography and geology. Most importantly though, our study revealed that a shift towards warmer temperatures and lower precipitation regimes will lead to a change of the spatial distribution of RSGs towards steppe soils that store less carbon, i.e. a decrease of spatial extent of Phaeozems and an increase of spatial extent of Chernozems and Kastanozems.
Combinations of runoff characteristics are commonly used to represent distinct conceptual models of stormflow generation. In this study, three runoff characteristics: hydrograph response, time source of runoff water, and flow path are used to classify catchments. Published data from the scientific literature are used to provide evidence from small, forested catchments. Each catchment was assigned to one of the eight conceptual models, depending on the combination of quick/slow response, old/new water, and overland/subsurface flow. A standard procedure was developed to objectively diagnose the predominant conceptual model of stormflow generation for each catchment and assess its temporal and spatial support. The literature survey yielded 42 catchments, of which 30 catchments provide a complete set of qualitative runoff characteristics resulting in one of the eight conceptual models. The majority of these catchments classify as subsurface flow path dominated. No catchments were found for conceptual models representing combinations of quick response-new water-subsurface flow (SSF), slow-new-SSF, slow-old-overland flow (OF) nor new-slow-OF. Of the 30 qualitatively classified catchments, 24 provide a complete set of quantitative measures. In summary, the field support is strong for 19 subsurface-dominated catchments and is weak for 5 surface flow path dominated catchments (six catchments had insufficient quantitative data). Two alternative explanations exist for the imbalance of field support between the two flow path classes: (1) the selection of research catchments in past field studies was mainly to explain quick hydrograph response in subsurface dominated catchments; (2) catchments with prevailing subsurface flow paths are more common in nature. We conclude that the selection of research catchments needs to cover a wider variety of environmental conditions which should lead to a broader, and more widely applicable, spectrum of resulting conceptual models and process mechanisms. This is a prerequisite in studies where catchment organization and similarity approaches are used to develop catchment classification systems in order to regionalize stormflow.
Draft Genome Sequence of Nocardioides alcanivorans NGK65(T), a Hexadecane-Degrading Bacterium
(2022)
The Gram-positive bacterium Nocardioides alcanivorans NGK65(T) was isolated from plastic-polluted soil and cultivated on medium with polyethylene as the single carbon source. Nanopore sequencing revealed the presence of candidate enzymes for the biodegradation of polyethylene. Here, we report the draft genome of this newly described member of the terrestrial plastisphere.
This review presents a compositional database of primary anatectic granitoid magmas, entirely based on melt inclusions (MI) in high-grade metamorphic rocks. Although MI are well known to igneous petrologists and have been extensively studied in intrusive and extrusive rocks, MI in crustal rocks that have undergone anatexis (migmatites and granulites) are a novel subject of research. They are generally trapped along the heating path by peritectic phases produced by incongruent melting reactions. Primary MI in high-grade metamorphic rocks are small, commonly 5-10 pm in diameter, and their most common mineral host is peritectic garnet. In most cases inclusions have crystallized into a cryptocrystalline aggregate and contain a granitoid phase assemblage (nanogranitoid inclusions) with quartz, K-feldspar, plagioclase, and one or two mica depending on the particular circumstances. After their experimental remelting under high-confining pressure, nanogranitoid MI can be analyzed combining several techniques (EMP, LA-ICP-MS, NanoSIMS, Raman). The trapped melt is granitic and metaluminous to peraluminous, and sometimes granodioritic, tonalitic, and trondhjemitic in composition, in agreement with the different P-T-a(H2o) conditions of melting and protolith composition, and overlap the composition of experimental glasses produced at similar conditions. Being trapped along the up-temperature trajectory as opposed to classic MI in igneous rocks formed during down-temperature magma crystallization fundamental information provided by nanogranitoid MI is the pristine composition of the natural primary anatectic melt for the specific rock under investigation. So far similar to 600 nanogranitoid MI, coming from several occurrences from different geologic and geodynamic settings and ages, have been characterized. Although the compiled MI database should be expanded to other potential sources of crustal magmas, MI data collected so far can be already used as natural "starting-point" compositions to track the processes involved in formation and evolution of granitoid magmas.
We present a wavelet coherence method that is capable of displaying local coherence information between two seismic stations in the sense of a spectrogram. We have analyzed the vertical components of a 20-min-long time series from four stations that were situated in the seismic near field of Stromboli volcano. Typical volcanic seismic signals recorded in the near field of Stromboli volcano consist of continuous volcanic tremor superimposed on frequent Strombolian explosion signals. The tremor exhibits a banded and frequency-stable structure, whereas the broadband explosion signals span two or three frequency decades. We demonstrate that signals related to explosion earthquakes are strongly correlated within the network over 1.5 frequency decades. Using synthetic data, we show how coherent signal portions can be extracted out of noisy data using a coherence-filtering method. A time delay analysis using coherence information results in a coarse source location estimation that lies within the crater region. With the exception of randomly fluctuating coherence peaks, low correlations have been observed in the characteristic bands that are assumed to be generated by continuous tremor. In the low-frequency band that is related to the ocean microseisms (period approximate to 4-8 sec), we observe mostly high correlation that breaks down during the appearance of explosion earthquake signals. Based on further analysis using the inverse wavelet transformation, we propose a model that describes the breakdown phenomenon as a superposition of two independent events
We report the results of our investigations on the catchment area, surface sediments, and hydrology of the monsoonal Lonar Lake, central India. Our results indicate that the lake is currently stratified with an anoxic bottom layer, and there is a spatial heterogeneity in the sensitivity of sediment parameters to different environmental processes. In the shallow (0-5 m) near shore oxic-suboxic environments the lithogenic and terrestrial organic content is high and spatially variable, and the organics show degradation in the oxic part. Due to aerial exposure resulting from lake level changes of at least 3m, the evaporitic carbonates are not completely preserved. In the deep water (>5 m) anoxic environment the lithogenics are uniformly distributed and the delta C-13 is an indicator not only for aquatic vs. terrestrial plants but also of lake pH and salinity. The isotopic composition of the evaporites is dependent not only on the isotopic composition of source water (monsoon rainfall and stream inflow) and evaporation, but is also influenced by proximity to the isotopically depleted stream inflow. We conclude that in the deep water environment lithogenic content, and isotopic composition of organic matter can be used for palaeoenvironmental reconstruction.
The imagination of clearly separated core-shell structures is already outdated by the fact, that the nanoparticle core-shell structures remain in terms of efficiency behind their respective bulk material due to intermixing between core and shell dopant ions. In order to optimize the photoluminescence of core-shell UCNP the intermixing should be as small as possible and therefore, key parameters of this process need to be identified. In the present work the Ln(III) ion migration in the host lattices NaYF4 and NaGdF4 was monitored. These investigations have been performed by laser spectroscopy with help of lanthanide resonance energy transfer (LRET) between Eu(III) as donor and Pr(III) or Nd(III) as acceptor. The LRET is evaluated based on the Forster theory. The findings corroborate the literature and point out the migration of ions in the host lattices. Based on the introduced LRET model, the acceptor concentration in the surrounding of one donor depends clearly on the design of the applied core-shell-shell nanoparticles. In general, thinner intermediate insulating shells lead to higher acceptor concentration, stronger quenching of the Eu(III) donor and subsequently stronger sensitization of the Pr(III) or the Nd(III) acceptors. The choice of the host lattice as well as of the synthesis temperature are parameters to be considered for the intermixing process.
Surface displacement at volcanic edifices is related to subsurface processes associated with magma movements, fluid transfers within the volcano edifice and gravity-driven deformation processes. Understanding of associated ground displacements is of importance for assessment of volcanic hazards. For example, volcanic unrest is often preceded by surface uplift, caused by magma intrusion and followed by subsidence, after the withdrawal of magma. Continuous monitoring of the surface displacement at volcanoes therefore might allow the forecasting of upcoming eruptions to some extent. In geophysics, the measured surface displacements allow the parameters of possible deformation sources to be estimated through analytical or numerical modeling. This is one way to improve the understanding of subsurface processes acting at volcanoes. Although the monitoring of volcanoes has significantly improved in the last decades (in terms of technical advancements and number of monitored volcanoes), the forecasting of volcanic eruptions remains puzzling. In this work I contribute towards the understanding of the subsurface processes at volcanoes and thus to the improvement of volcano eruption forecasting. I have investigated the displacement field of Llaima volcano in Chile and of Tendürek volcano in East Turkey by using synthetic aperture radar interferometry (InSAR). Through modeling of the deformation sources with the extracted displacement data, it was possible to gain insights into potential subsurface processes occurring at these two volcanoes that had been barely studied before. The two volcanoes, although of very different origin, composition and geometry, both show a complexity of interacting deformation sources. At Llaima volcano, the InSAR technique was difficult to apply, due to the large decorrelation of the radar signal between the acquisition of images. I developed a model-based unwrapping scheme, which allows the production of reliable displacement maps at the volcano that I used for deformation source modeling. The modeling results show significant differences in pre- and post-eruptive magmatic deformation source parameters. Therefore, I conjecture that two magma chambers exist below Llaima volcano: a post-eruptive deep one and a shallow one possibly due to the pre-eruptive ascent of magma. Similar reservoir depths at Llaima have been confirmed by independent petrologic studies. These reservoirs are interpreted to be temporally coupled. At Tendürek volcano I have found long-term subsidence of the volcanic edifice, which can be described by a large, magmatic, sill-like source that is subject to cooling contraction. The displacement data in conjunction with high-resolution optical images, however, reveal arcuate fractures at the eastern and western flank of the volcano. These are most likely the surface expressions of concentric ring-faults around the volcanic edifice that show low magnitudes of slip over a long time. This might be an alternative mechanism for the development of large caldera structures, which are so far assumed to be generated during large catastrophic collapse events. To investigate the potential subsurface geometry and relation of the two proposed interacting sources at Tendürek, a sill-like magmatic source and ring-faults, I have performed a more sophisticated numerical modeling approach. The optimum source geometries show, that the size of the sill-like source was overestimated in the simple models and that it is difficult to determine the dip angle of the ring-faults with surface displacement data only. However, considering physical and geological criteria a combination of outward-dipping reverse faults in the west and inward-dipping normal faults in the east seem to be the most likely. Consequently, the underground structure at the Tendürek volcano consists of a small, sill-like, contracting, magmatic source below the western summit crater that causes a trapdoor-like faulting along the ring-faults around the volcanic edifice. Therefore, the magmatic source and the ring-faults are also interpreted to be temporally coupled. In addition, a method for data reduction has been improved. The modeling of subsurface deformation sources requires only a relatively small number of well distributed InSAR observations at the earth’s surface. Satellite radar images, however, consist of several millions of these observations. Therefore, the large amount of data needs to be reduced by several orders of magnitude for source modeling, to save computation time and increase model flexibility. I have introduced a model-based subsampling approach in particular for heterogeneously-distributed observations. It allows a fast calculation of the data error variance-covariance matrix, also supports the modeling of time dependent displacement data and is, therefore, an alternative to existing methods.
Seismic wide-angle data were collected along a 40-km-long profile centered at the geothermal research well GrSk 3/90 in the Northeast German Basin. Tomographic inversion of travel time data provided a velocity and a vertical velocity gradient model, indicative of Cenozoic to Pre-Permian sediments. Wide-angle reflections are modeled and interpreted as top Zechstein and top Pre-Permian. Changes in velocity gradients are interpreted as the transition from mechanical to chemical compaction at 2-3 km depth, and localized salt structures are imaged, suggesting a previously unknown salt pillow in the southern part of the seismic profile. The Zechstein salt shows decreased velocities in the adjacent salt pillows compared to the salt lows, which is confirmed by sonic log data. This decrease in velocity could be explained by the mobilization of less dense salt, which moved and formed the salt pillows, whereas the denser salt remained in place at the salt lows. We interpret a narrow subvertical low-velocity zone under the salt pillow at GrSk 3/ 90 as a fault in the deep Permian to Pre-Permian. This WNW-ESE trending fault influenced the location of the salt tectonics and led to the formation of a fault-bounded graben in the Rotliegend sandstones with optimal mechanical conditions for geothermal production. Thermal modeling showed that salt pillows are related to chimney effects, a decrease in temperature, and increasing velocity. The assumed variations in salt lithology, density, and strain must thus be even higher to compensate for the temperature effect.
Black shales are sedimentary rocks with a high content of organic carbon, which leads to a dark grayish to black color. Due to their potential to contain oil or gas, black shales are of great interest for the support of the worldwide energy supply. An integrated seismic investigation of the Lower Palaeozoic black shales was carried out at the Danish island Bornholm to locate the shallow-lying Alum Shale layer and its surrounding formations and to characterize its potential as a source rock. Therefore, two seismic experiments at a total of three crossing profiles were carried out in October 2010 and in June 2012 in the southern part of the island. Two different active measurements were conducted with either a weight drop source or a minivibrator. Additionally, the ambient noise field was recorded at the study location over a time interval of about one day, and also a laboratory analysis of borehole samples was carried out. The seismic profiles were positioned as close as possible to two scientific boreholes which were used for comparative purposes. The seismic field data was analyzed with traveltime tomography, surface wave inversion and seismic interferometry to obtain the P-wave and S-wave velocity models of the subsurface. The P-wave velocity models which were determined for all three profiles clearly locate the Alum Shale layer between the Komstad Limestone layer on top and the Læså Sandstone Formation at the base of the models. The black shale layer has P-wave velocities around 3 km/s which are lower compared to the adjacent formations. Due to a very good agreement of the sonic log and the vertical velocity profiles of the two seismic lines, which are directly crossing the borehole where the sonic log was conducted, the reliability of the traveltime tomography is proven. A correlation of the seismic velocities with the content of organic carbon is an important task for the characterization of the reservoir properties of a black shale formation. It is not possible without calibration but in combination with a full 2D tomographic image of the subsurface it gives the subsurface distribution of the organic material. The S-wave model obtained with surface wave inversion of the vibroseis data of one of the profiles images the Alum Shale layer also very well with S-wave velocities around 2 km/s. Although individual 1D velocity models for each of the source positions were determined, the subsurface S-wave velocity distribution is very uniform with a good match between the single models. A really new approach described here is the application of seismic interferometry to a really small study area and a quite short time interval. Also new is the selective procedure of only using time windows with the best crosscorrelation signals to achieve the final interferograms. Due to the small scale of the interferometry even P-wave signals can be observed in the final crosscorrelations. In the laboratory measurements the seismic body waves were recorded for different pressure and temperature stages. Therefore, samples of different depths of the Alum Shale were available from one of the scientific boreholes at the study location. The measured velocities have a high variance with changing pressure or temperature. Recordings with wave propagation both parallel and perpendicular to the bedding of the samples reveal a great amount of anisotropy for the P-wave velocity, whereas the S-wave velocity is almost independent of the wave direction. The calculated velocity ratio is also highly anisotropic with very low values for the perpendicular samples and very high values for the parallel ones. Interestingly, the laboratory velocities of the perpendicular samples are comparable to the velocities of the field experiments indicating that the field measurements are sensitive to wave propagation in vertical direction. The velocity ratio is also calculated with the P-wave and S-wave velocity models of the field experiments. Again, the Alum Shale can be clearly separated from the adjacent formations because it shows overall very low vP/vS ratios around 1.4. The very low velocity ratio indicates the content of gas in the black shale formation. With the combination of all the different methods described here, a comprehensive interpretation of the seismic response of the black shale layer can be made and the hydrocarbon source rock potential can be estimated.
Temperature is a key factor controlling plant growth and vitality in the temperate climates of the mid-latitudes like in vast parts of the European continent. Beyond the effect of average conditions, the timings and magnitudes of temperature extremes play a particularly crucial role, which needs to be better understood in the context of projected future rises in the frequency and/or intensity of such events. In this work, we employ event coincidence analysis (ECA) to quantify the likelihood of simultaneous occurrences of extremes in daytime land surface temperature anomalies (LSTAD) and the normalized difference vegetation index (NDVI). We perform this analysis for entire Europe based upon remote sensing data, differentiating between three periods corresponding to different stages of plant development during the growing season. In addition, we analyze the typical elevation and land cover type of the regions showing significantly large event coincidences rates to identify the most severely affected vegetation types. Our results reveal distinct spatio-temporal impact patterns in terms of extraordinarily large co-occurrence rates between several combinations of temperature and NDVI extremes. Croplands are among the most frequently affected land cover types, while elevation is found to have only a minor effect on the spatial distribution of corresponding extreme weather impacts. These findings provide important insights into the vulnerability of European terrestrial ecosystems to extreme temperature events and demonstrate how event-based statistics like ECA can provide a valuable perspective on environmental nexuses.
Climatic variations and human activity now and increasingly in the future cause land cover changes and introduce perturbations in the terrestrial carbon reservoirs in vegetation, soil and detritus. Optical remote sensing and in particular Imaging Spectroscopy has shown the potential to quantify land surface parameters over large areas, which is accomplished by taking advantage of the characteristic interactions of incident radiation and the physico-chemical properties of a material. The objective of this thesis is to quantify key soil parameters, including soil organic carbon, using field and Imaging Spectroscopy. Organic carbon, iron oxides and clay content are selected to be analyzed to provide indicators for ecosystem function in relation to land degradation, and additionally to facilitate a quantification of carbon inventories in semiarid soils. The semiarid Albany Thicket Biome in the Eastern Cape Province of South Africa is chosen as study site. It provides a regional example for a semiarid ecosystem that currently undergoes land changes due to unadapted management practices and furthermore has to face climate change induced land changes in the future. The thesis is divided in three methodical steps. Based on reflectance spectra measured in the field and chemically determined constituents of the upper topsoil, physically based models are developed to quantify soil organic carbon, iron oxides and clay content. Taking account of the benefits limitations of existing methods, the approach is based on the direct application of known diagnostic spectral features and their combination with multivariate statistical approaches. It benefits from the collinearity of several diagnostic features and a number of their properties to reduce signal disturbances by influences of other spectral features. In a following step, the acquired hyperspectral image data are prepared for an analysis of soil constituents. The data show a large spatial heterogeneity that is caused by the patchiness of the natural vegetation in the study area that is inherent to most semiarid landscapes. Spectral mixture analysis is performed and used to deconvolve non-homogenous pixels into their constituent components. For soil dominated pixels, the subpixel information is used to remove the spectral influence of vegetation and to approximate the pure spectral signature coming from the soil. This step is an integral part when working in natural non-agricultural areas where pure bare soil pixels are rare. It is identified as the largest benefit within the multi-stage methodology, providing the basis for a successful and unbiased prediction of soil constituents from hyperspectral imagery. With the proposed approach it is possible (1) to significantly increase the spatial extent of derived information of soil constituents to areas with about 40 % vegetation coverage and (2) to reduce the influence of materials such as vegetation on the quantification of soil constituents to a minimum. Subsequently, soil parameter quantities are predicted by the application of the feature-based soil prediction models to the maps of locally approximated soil signatures. Thematic maps showing the spatial distribution of the three considered soil parameters in October 2009 are produced for the Albany Thicket Biome of South Africa. The maps are evaluated for their potential to detect erosion affected areas as effects of land changes and to identify degradation hot spots in regard to support local restoration efforts. A regional validation, carried out using available ground truth sites, suggests remaining factors disturbing the correlation of spectral characteristics and chemical soil constituents. The approach is developed for semiarid areas in general and not adapted to specific conditions in the study area. All processing steps of the developed methodology are implemented in software modules, where crucial steps of the workflow are fully automated. The transferability of the methodology is shown for simulated data of the future EnMAP hyperspectral satellite. Soil parameters are successfully predicted from these data despite intense spectral mixing within the lower spatial resolution EnMAP pixels. This study shows an innovative approach to use Imaging Spectroscopy for mapping of key soil constituents, including soil organic carbon, for large areas in a non-agricultural ecosystem and under consideration of a partially vegetation coverage. It can contribute to a better assessment of soil constituents that describe ecosystem processes relevant to detect and monitor land changes. The maps further provide an assessment of the current carbon inventory in soils, valuable for carbon balances and carbon mitigation products.
The Seismic Hazard Inferred from Tectonics based on the Global Strain Rate Map (SHIFT_GSRM) earthquake forecast was designed to provide high-resolution estimates of global shallow seismicity to be used in seismic hazard assessment. This model combines geodetic strain rates with global earthquake parameters to characterize long-term rates of seismic moment and earthquake activity. Although SHIFT_GSRM properly computes seismicity rates in seismically active continental regions, it underestimates earthquake rates in subduction zones by an average factor of approximately 3. We present a complementary method to SHIFT_GSRM to more accurately forecast earthquake rates in 37 subduction segments, based on the conservation of moment principle and the use of regional interface seismicity parameters, such as subduction dip angles, corner magnitudes, and coupled seismogenic thicknesses. In seven progressive steps, we find that SHIFT_GSRM earthquake-rate underpredictions are mainly due to the utilization of a global probability function of seismic moment release that poorly captures the great variability among subduction megathrust interfaces. Retrospective test results show that the forecast is consistent with the observations during the 1 January 1977 to 31 December 2014 period. Moreover, successful pseudoprospective evaluations for the 1 January 2015 to 31 December 2018 period demonstrate the power of the regionalized earthquake model to properly estimate subduction-zone seismicity.
One third of the world's population lives in areas where earthquakes causing at least slight damage are frequently expected. Thus, the development and testing of global seismicity models is essential to improving seismic hazard estimates and earthquake-preparedness protocols for effective disaster-risk mitigation. Currently, the availability and quality of geodetic data along plate-boundary regions provides the opportunity to construct global models of plate motion and strain rate, which can be translated into global maps of forecasted seismicity. Moreover, the broad coverage of existing earthquake catalogs facilitates in present-day the calibration and testing of global seismicity models. As a result, modern global seismicity models can integrate two independent factors necessary for physics-based, long-term earthquake forecasting, namely interseismic crustal strain accumulation and sudden lithospheric stress release.
In this dissertation, I present the construction of and testing results for two global ensemble seismicity models, aimed at providing mean rates of shallow (0-70 km) earthquake activity for seismic hazard assessment. These models depend on the Subduction Megathrust Earthquake Rate Forecast (SMERF2), a stationary seismicity approach for subduction zones, based on the conservation of moment principle and the use of regional "geodesy-to-seismicity" parameters, such as corner magnitudes, seismogenic thicknesses and subduction dip angles. Specifically, this interface-earthquake model combines geodetic strain rates with instrumentally-recorded seismicity to compute long-term rates of seismic and geodetic moment. Based on this, I derive analytical solutions for seismic coupling and earthquake activity, which provide this earthquake model with the initial abilities to properly forecast interface seismicity. Then, I integrate SMERF2 interface-seismicity estimates with earthquake computations in non-subduction zones provided by the Seismic Hazard Inferred From Tectonics based on the second iteration of the Global Strain Rate Map seismicity approach to construct the global Tectonic Earthquake Activity Model (TEAM). Thus, TEAM is designed to reduce number, and potentially spatial, earthquake inconsistencies of its predecessor tectonic earthquake model during the 2015-2017 period. Also, I combine this new geodetic-based earthquake approach with a global smoothed-seismicity model to create the World Hybrid Earthquake Estimates based on Likelihood scores (WHEEL) model. This updated hybrid model serves as an alternative earthquake-rate approach to the Global Earthquake Activity Rate model for forecasting long-term rates of shallow seismicity everywhere on Earth.
Global seismicity models provide scientific hypotheses about when and where earthquakes may occur, and how big they might be. Nonetheless, the veracity of these hypotheses can only be either confirmed or rejected after prospective forecast evaluation. Therefore, I finally test the consistency and relative performance of these global seismicity models with independent observations recorded during the 2014-2019 pseudo-prospective evaluation period. As a result, hybrid earthquake models based on both geodesy and seismicity are the most informative seismicity models during the testing time frame, as they obtain higher information scores than their constituent model components. These results support the combination of interseismic strain measurements with earthquake-catalog data for improved seismicity modeling. However, further prospective evaluations are required to more accurately describe the capacities of these global ensemble seismicity models to forecast longer-term earthquake activity.
Hyperspectral remote sensing of the spatial and temporal heterogeneity of low Arctic vegetation
(2019)
Arctic tundra ecosystems are experiencing warming twice the global average and Arctic vegetation is responding in complex and heterogeneous ways. Shifting productivity, growth, species composition, and phenology at local and regional scales have implications for ecosystem functioning as well as the global carbon and energy balance. Optical remote sensing is an effective tool for monitoring ecosystem functioning in this remote biome. However, limited field-based spectral characterization of the spatial and temporal heterogeneity limits the accuracy of quantitative optical remote sensing at landscape scales. To address this research gap and support current and future satellite missions, three central research questions were posed:
• Does canopy-level spectral variability differ between dominant low Arctic vegetation communities and does this variability change between major phenological phases?
• How does canopy-level vegetation colour images recorded with high and low spectral resolution devices relate to phenological changes in leaf-level photosynthetic pigment concentrations?
• How does spatial aggregation of high spectral resolution data from the ground to satellite scale influence low Arctic tundra vegetation signatures and thereby what is the potential of upcoming hyperspectral spaceborne systems for low Arctic vegetation characterization?
To answer these questions a unique and detailed database was assembled. Field-based canopy-level spectral reflectance measurements, nadir digital photographs, and photosynthetic pigment concentrations of dominant low Arctic vegetation communities were acquired at three major phenological phases representing early, peak and late season. Data were collected in 2015 and 2016 in the Toolik Lake Research Natural Area located in north central Alaska on the North Slope of the Brooks Range. In addition to field data an aerial AISA hyperspectral image was acquired in the late season of 2016. Simulations of broadband Sentinel-2 and hyperspectral Environmental and Mapping Analysis Program (EnMAP) satellite reflectance spectra from ground-based reflectance spectra as well as simulations of EnMAP imagery from aerial hyperspectral imagery were also obtained.
Results showed that canopy-level spectral variability within and between vegetation communities differed by phenological phase. The late season was identified as the most discriminative for identifying many dominant vegetation communities using both ground-based and simulated hyperspectral reflectance spectra. This was due to an overall reduction in spectral variability and comparable or greater differences in spectral reflectance between vegetation communities in the visible near infrared spectrum.
Red, green, and blue (RGB) indices extracted from nadir digital photographs and pigment-driven vegetation indices extracted from ground-based spectral measurements showed strong significant relationships. RGB indices also showed moderate relationships with chlorophyll and carotenoid pigment concentrations. The observed relationships with the broadband RGB channels of the digital camera indicate that vegetation colour strongly influences the response of pigment-driven spectral indices and digital cameras can track the seasonal development and degradation of photosynthetic pigments.
Spatial aggregation of hyperspectral data from the ground to airborne, to simulated satel-lite scale was influenced by non-photosynthetic components as demonstrated by the distinct shift of the red edge to shorter wavelengths. Correspondence between spectral reflectance at the three scales was highest in the red spectrum and lowest in the near infra-red. By artificially mixing litter spectra at different proportions to ground-based spectra, correspondence with aerial and satellite spectra increased. Greater proportions of litter were required to achieve correspondence at the satellite scale.
Overall this thesis found that integrating multiple temporal, spectral, and spatial data is necessary to monitor the complexity and heterogeneity of Arctic tundra ecosystems. The identification of spectrally similar vegetation communities can be optimized using non-peak season hyperspectral data leading to more detailed identification of vegetation communities. The results also highlight the power of vegetation colour to link ground-based and satellite data. Finally, a detailed characterization non-photosynthetic ecosystem components is crucial for accurate interpretation of vegetation signals at landscape scales.
The first step in the estimation of probabilistic seismic hazard in a region commonly consists of the definition and characterization of the relevant seismic sources. Because in low-seismicity regions seismicity is often rather diffuse and faults are difficult to identify, large areal source zones are mostly used. The corresponding hypothesis is that seismicity is uniformly distributed inside each areal seismic source zone. In this study, the impact of this hypothesis on the probabilistic hazard estimation is quantified through the generation of synthetic spatial seismicity distributions. Fractal seismicity distributions are generated inside a given source zone and probabilistic hazard is computed for a set of sites located inside this zone. In our study, the impact of the spatial seismicity distribution is defined as the deviation from the hazard value obtained for a spatially uniform seismicity distribution. From the generation of a large number of synthetic distributions, the correlation between the fractal dimension D and the impact is derived. The results show that the assumption of spatially uniform seismicity tends to bias the hazard to higher values. The correlation can be used to determine the systematic biases and uncertainties for hazard estimations in real cases, where the fractal dimension has been determined. We apply the technique in Germany (Cologne area) and in France (Alps).
Ground-motion prediction equations (GMPE) are essential in probabilistic seismic hazard studies for estimating the ground motions generated by the seismic sources. In low-seismicity regions, only weak motions are available during the lifetime of accelerometric networks, and the equations selected for the probabilistic studies are usually models established from foreign data. Although most GMPEs have been developed for magnitudes 5 and above, the minimum magnitude often used in probabilistic studies in low-seismicity regions is smaller. Disaggregations have shown that, at return periods of engineering interest, magnitudes less than 5 may be contributing to the hazard. This paper presents the testing of several GMPEs selected in current international and national probabilistic projects against weak motions recorded in France (191 recordings with source-site distances up to 300 km, 3:8 <= M-w <= 4:5). The method is based on the log-likelihood value proposed by Scherbaum et al. (2009). The best-fitting models (approximately 2:5 <= LLH <= 3:5) over the whole frequency range are the Cauzzi and Faccioli (2008), Akkar and Bommer (2010), and Abrahamson and Silva (2008) models. No significant regional variation of ground motions is highlighted, and the magnitude scaling could be the predominant factor in the control of ground-motion amplitudes. Furthermore, we take advantage of a rich Japanese dataset to run tests on randomly selected low-magnitude subsets, and confirm that a dataset of similar to 190 observations, the same size as the French dataset, is large enough to obtain stable LLH estimates. Additionally we perform the tests against larger magnitudes (5-7) from the Japanese dataset. The ranking of models is partially modified, indicating a magnitude scaling effect for some of the models, and showing that extrapolating testing results obtained from low-magnitude ranges to higher magnitude ranges is not straightforward.
In low-seismicity regions, such as France or Germany, the estimation of probabilistic seismic hazard must cope with the difficult identification of active faults and with the low amount of seismic data available. Since the probabilistic hazard method was initiated, most studies assume a Poissonian occurrence of earthquakes. Here we propose a method that enables the inclusion of time and space dependences between earthquakes into the probabilistic estimation of hazard. Combining the seismicity model Epidemic Type Aftershocks-Sequence (ETAS) with a Monte Carlo technique, aftershocks are naturally accounted for in the hazard determination. The method is applied to the Pyrenees region in Southern France. The impact on hazard of declustering and of the usual assumption that earthquakes occur according to a Poisson process is quantified, showing that aftershocks contribute on average less than 5 per cent to the probabilistic hazard, with an upper bound around 18 per cent
The results of this study clearly identify four key parameters controlling the estimation of probabilistic seismic hazard assessment (PSHA) in France in the framework of the Cornell-McGuire method. Results in terms of peak ground acceleration demonstrate the equally high impact, at all return periods, of the choice of truncation of the predicted ground-motion distribution (at + 2sigma) and of the choice between two different magnitude-intensity correlations. The choice of minimum magnitude (3.5/4.5) on hazard estimates can have an important impact at small return periods (<1000 years), whereas the maximum magnitude (6.5/7.0), on the other hand, is not a key parameter even at large return periods (10,000 years). This hierarchy of impacts is maintained at lower frequencies down to 5 Hz. Below 5 Hz, the choice of the maximum magnitude has a much greater impact, whereas the impact due to the choice of the minimum magnitude disappears. Moreover, variability due to catalog uncertainties is also quantified; these uncertainties that underly all hazard results can engender as high a variability as the controlling parameters. Parameter impacts, calculated at the centers of each source zone, show a linear trend with the seismicity models of the zone, demonstrating the lack of contributions coming from neighboring zones. Indeed, the region of influence that contributes to the PSHA estimate at a given site decreases with increasing return periods. The resulting overall variability in hazard estimates due to input uncertainties is quantified through a logic tree, obtained coefficients of variation vary between 10% and 20%. Until better physical models are obtained, the uncertainty on hazard estimates may be reduced by working on an appropriate magnitude-intensity correlation
New age data have been obtained to time constrain the recent Quaternary volcanism of El Hierro (Canary Islands) and to estimate its recurrence rate. We have carried out Ar-40/Ar-39 geochronology on samples spanning the entire volcanostratigraphic sequence of the island and C-14 geochronology on the most recent eruption on the northeast rift of the island: 2280 +/- 30 yr BP. We combine the new absolute data with a revision of published ages onshore, some of which were identified through geomorphological criteria (relative data). We present a revised and updated chronology of volcanism for the last 33 ka that we use to estimate the maximum eruptive recurrence of the island. The number of events per year determined is 9.7 x 10(-4) for the emerged part of the island, which means that, as a minimum, one eruption has occurred approximately every 1000 years. This highlights the need of more geochronological data to better constrain the eruptive recurrence of El Hierro. (C) 2015 Elsevier Ltd. All rights reserved.
Beta diversity is a conceptual link between diversity at local and regional scales. Various additional methodologies of quantifying this and related phenomena have been applied. Among them, measures of pairwise (dis)similarity of sites are particularly popular. Undersampling, i.e. not recording all taxa present at a site, is a common situation in ecological data. Bias in many metrics related to beta diversity must be expected, but only few studies have explicitly investigated the properties of various measures under undersampling conditions. On the basis of an empirical data set, representing near-complete local inventories of the Lepidoptera from an isolated Pacific island, as well as simulated communities with varying properties, we mimicked different levels of undersampling. We used 14 different approaches to quantify beta diversity, among them dataset-wide multiplicative partitioning (i.e. true beta diversity') and pairwise site x site dissimilarities. We compared their values from incomplete samples to true results from the full data. We used these comparisons to quantify undersampling bias and we calculated correlations of the dissimilarity measures of undersampled data with complete data of sites. Almost all tested metrics showed bias and low correlations under moderate to severe undersampling conditions (as well as deteriorating precision, i.e. large chance effects on results). Measures that used only species incidence were very sensitive to undersampling, while abundance-based metrics with high dependency on the distribution of the most common taxa were particularly robust. Simulated data showed sensitivity of results to the abundance distribution, confirming that data sets of high evenness and/or the application of metrics that are strongly affected by rare species are particularly sensitive to undersampling. The class of beta measure to be used should depend on the research question being asked as different metrics can lead to quite different conclusions even without undersampling effects. For each class of metric, there is a trade-off between robustness to undersampling and sensitivity to rare species. In consequence, using incidence-based metrics carries a particular risk of false conclusions when undersampled data are involved. Developing bias corrections for such metrics would be desirable.
The seismicity pattern along the San Andreas fault near Parkfield and Cholame, California, varies distinctly over a length of only fifty kilometres. Within the brittle crust, the presence of frictionally weak minerals, fault-weakening high fluid pressures and chemical weakening are considered possible causes of an anomalously weak fault northwest of Parkfield(1-4). Non-volcanic tremor from lower-crustal and upper-mantle depths(5-7) is most pronounced about thirty kilometres southeast of Parkfield and is thought to be associated with high pore-fluid pressures at depth(8). Here we present geophysical evidence of fluids migrating into the creeping section of the San Andreas fault that seem to originate in the region of the uppermost mantle that also stimulates tremor, and evidence that along-strike variations in tremor activity and amplitude are related to strength variations in the lower crust and upper mantle. Interconnected fluids can explain a deep zone of anomalously low electrical resistivity that has been imaged by magnetotelluric data southwest of the Parkfield-Cholame segment. Near Cholame, where fluids seem to be trapped below a high-resistivity cap, tremor concentrates adjacent to the inferred fluids within a mechanically strong zone of high resistivity. By contrast, sub-vertical zones of low resistivity breach the entire crust near the drill hole of the San Andreas Fault Observatory at Depth, northwest of Parkfield, and imply pathways for deep fluids into the eastern fault block, coincident with a mechanically weak crust and the lower tremor amplitudes in the lower crust. Fluid influx to the fault system is consistent with hypotheses of fault-weakening high fluid pressures in the brittle crust.
Eight d-metal-containing N-butylpyridinium ionic liquids (ILs) with the nominal composition (C4Py)2[Ni0.5M0.5Cl4] or (C4Py)2[Zn0.5M0.5Cl4] (M = Cu, Co, Mn, Ni, Zn; C4Py = N-butylpyridinium) were synthesized, characterized, and investigated for their optical properties. Single crystal and powder X-ray analysis shows that the compounds are isostructural to existing examples based on other d-metal ions. Inductively coupled plasma optical emission spectroscopy measurements confirm that the metal/metal ratio is around 50 : 50. UV-Vis spectroscopy shows that the optical absorption can be tuned by selection of the constituent metals. Moreover, the compounds can act as an optical sensor for the detection of gases such as ammonia as demonstrated via a simple prototype setup.
Causes for slow weathering and erosion in the steep, warm, monsoon-subjected Highlands of Sri Lanka
(2018)
In the Highlands of Sri Lanka, erosion and chemical weathering rates are among the lowest for global mountain denudation. In this tropical humid setting, highly weathered deep saprolite profiles have developed from high-grade metamorphic charnockite during spheroidal weathering of the bedrock. The spheroidal weathering produces rounded corestones and spalled rindlets at the rock-saprolite interface. I used detailed textural, mineralogical, chemical, and electron-microscopic (SEM, FIB, TEM) analyses to identify the factors limiting the rate of weathering front advance in the profile, the sequence of weathering reactions, and the underlying mechanisms. The first mineral attacked by weathering was found to be pyroxene initiated by in situ Fe oxidation, followed by in situ biotite oxidation. Bulk dissolution of the primary minerals is best described with a dissolution – re-precipitation process, as no chemical gradients towards the mineral surface and sharp structural boundaries are observed at the nm scale. Only the local oxidation in pyroxene and biotite is better described with an ion by ion process. The first secondary phases are oxides and amorphous precipitates from which secondary minerals (mainly smectite and kaolinite) form. Only for biotite direct solid state transformation to kaolinite is likely. The initial oxidation of pyroxene and biotite takes place in locally restricted areas and is relatively fast: log J = -11 molmin/(m2 s). However, calculated corestone-scale mineral oxidation rates are comparable to corestone-scale mineral dissolution rates: log R = -13 molpx/(m2 s) and log R = -15 molbt/(m2 s). The oxidation reaction results in a volume increase. Volumetric calculations suggest that this observed oxidation leads to the generation of porosity due to the formation of micro-fractures in the minerals and the bedrock allowing for fluid transport and subsequent dissolution of plagioclase. At the scale of the corestone, this fracture reaction is responsible for the larger fractures that lead to spheroidal weathering and to the formation of rindlets. Since these fractures have their origin from the initial oxidational induced volume increase, oxidation is the rate limiting parameter for weathering to take place. The ensuing plagioclase weathering leads to formation of high secondary porosity in the corestone over a distance of only a few cm and eventually to the final disaggregation of bedrock to saprolite. As oxidation is the first weathering reaction, the supply of O2 is a rate-limiting factor for chemical weathering. Hence, the supply of O2 and its consumption at depth connects processes at the weathering front with erosion at the surface in a feedback mechanism. The strength of the feedback depends on the relative weight of advective versus diffusive transport of O2 through the weathering profile. The feedback will be stronger with dominating diffusive transport. The low weathering rate ultimately depends on the transport of O2 through the whole regolith, and on lithological factors such as low bedrock porosity and the amount of Fe-bearing primary minerals. In this regard the low-porosity charnockite with its low content of Fe(II) bearing minerals impedes fast weathering reactions. Fresh weatherable surfaces are a pre-requisite for chemical weathering. However, in the case of the charnockite found in the Sri Lankan Highlands, the only process that generates these surfaces is the fracturing induced by oxidation. Tectonic quiescence in this region and low pre-anthropogenic erosion rate (attributed to a dense vegetation cover) minimize the rejuvenation of the thick and cohesive regolith column, and lowers weathering through the feedback with erosion.
In the Sri Lankan Highlands erosion and chemical weathering rates are among the lowest for global mountain denudation. In this tropical humid setting, highly weathered deep saprolite profiles have developed from high-grade metamorphic charnockite during spheroidal weathering of the bedrock. The spheroidal weathering produces rounded corestones and spalled rindlets at the rock-saprolite interface. We used detailed textural, mineralogical and chemical analyses to reconstruct the sequence of weathering reactions and their causes. The first mineral attacked by weathering was found to be pyroxene initiated by in situ Fe oxidation. Volumetric calculations suggest that this oxidation leads to the generation of porosity due to the formation of micro-fractures allowing for fluid transport and subsequent dissolution of biotite and plagioclase. The rapid ensuing plagioclase weathering leads to formation of high secondary porosity in the corestone over a distance of only a few cm and eventually to the final disaggregation of bedrock to saprolite. The first secondary phases are oxides or amorphous precipitates from which secondary minerals (mainly gibbsite, kaolinite and goethite) form. As oxidation is the first weathering reaction, the supply of O-2 is a rate-limiting factor for chemical weathering. Hence, the supply of O-2 and its consumption at depth connects processes at the weathering front with those at the Earth's surface in a feedback mechanism. The strength of the feedback depends on the relative weight of advective versus diffusive transport of O-2 through the weathering profile. The feedback will be stronger with dominating diffusive transport. The low weathering rate is explained by the nature of this feedback that is ultimately dependent on the transport of O-2 through the whole regolith, and on lithological factors such as low bedrock porosity and the amount of Fe-bearing primary minerals. Tectonic quiescence in this region and low pre-development erosion rate (attributed to a dense vegetation cover) minimize the rejuvenation of the thick and cohesive regolith column, finally leading to low denudation rates. (C) 2015 Elsevier B.V. All rights reserved.
The Misho complex in Northwest Iran is a prominent topographic massif bounded by well known active faults. Our new structural analysis of this area indicates that faulting has important role in the exhumation of this complex. The conjugate orientation of the North and South Misho Faults caused uplift in the Misho and exhumation of the Precambrian crystalline basement. Our structural and stratigraphic data shows that rapid uplift could have been initiation since the 21-22 Ma and exhumation rate was about 0.16 to 0.24 km/Ma. To refine this age, we performed U/Pb analysis of detrital zircon from the Upper Red Formation using LA-ICP-MS. We conducted AFT analysis on 6 basement samples from the hanging wall and 1 sample from the Upper Red Formation in the footwall NMF. Uplift in the hanging wall of NMF led to resting of sample 916 marl. This geochronologic and thermochronologic data shows that exhumation in the MC is diachronously along strike and affected by faults. The phase of exhumation is documented in the study area and entire Iranian plateau is related to the final closure of the Neo-Tethys and northward motion of the Arabian Plate.
Growing attention to phytoplankton mixotrophy as a trophic strategy has led to significant revisions of traditional pelagic food web models and ecosystem functioning. Although some empirical estimates of mixotrophy do exist, a much broader set of in situ measurements are required to (i) identify which organisms are acting as mixotrophs in real time and to (ii) assess the contribution of their heterotrophy to biogeochemical cycling. Estimates are needed through time and across space to evaluate which environmental conditions or habitats favour mixotrophy: conditions still largely unknown. We review methodologies currently available to plankton ecologists to undertake estimates of plankton mixotrophy, in particular nanophytoplankton phago-mixotrophy. Methods are based largely on fluorescent or isotopic tracers, but also take advantage of genomics to identify phylotypes and function. We also suggest novel methods on the cusp of use for phago-mixotrophy assessment, including single-cell measurements improving our capacity to estimate mixotrophic activity and rates in wild plankton communities down to the single-cell level. Future methods will benefit from advances in nanotechnology, micromanipulation and microscopy combined with stable isotope and genomic methodologies. Improved estimates of mixotrophy will enable more reliable models to predict changes in food web structure and biogeochemical flows in a rapidly changing world.
There are far-reaching conceptual similarities between bi-static surface georadar and post-stack, "zero-offset" seismic reflection data, which is expressed in largely identical processing flows. One important difference is, however, that standard deconvolution algorithms routinely used to enhance the vertical resolution of seismic data are notoriously problematic or even detrimental to the overall signal quality when applied to surface georadar data. We have explored various options for alleviating this problem and have tested them on a geologically well-constrained surface georadar dataset. Standard stochastic and direct deterministic deconvolution approaches proved to be largely unsatisfactory. While least-squares-type deterministic deconvolution showed some promise, the inherent uncertainties involved in estimating the source wavelet introduced some artificial "ringiness". In contrast, we found spectral balancing approaches to be effective, practical and robust means for enhancing the vertical resolution of surface georadar data, particularly, but not exclusively, in the uppermost part of the georadar section, which is notoriously plagued by the interference of the direct air- and groundwaves. For the data considered in this study, it can be argued that band- limited spectral blueing may provide somewhat better results than standard band-limited spectral whitening, particularly in the uppermost part of the section affected by the interference of the air- and groundwaves. Interestingly, this finding is consistent with the fact that the amplitude spectrum resulting from least-squares-type deterministic deconvolution is characterized by a systematic enhancement of higher frequencies at the expense of lower frequencies and hence is blue rather than white. It is also consistent with increasing evidence that spectral "blueness" is a seemingly universal, albeit enigmatic, property of the distribution of reflection coefficients in the Earth. Our results therefore indicate that spectral balancing techniques in general and spectral blueing in particular represent simple, yet effective means of enhancing the vertical resolution of surface georadar data and, in many cases, could turn out to be a preferable alternative to standard deconvolution approaches.
Carbonate minerals are common in both marine and lacustrine records, and are frequently used for paleoenvironmental reconstructions. The sedimentary sequence of the endorheic Dead Sea and its precursors contain aragonite laminae that provide a detailed sedimentary archive of climatic, hydrologic, limnologic and environmental conditions since the Pleistocene. However, the interpretation of these archives requires a detailed understanding of the constraints and mechanisms affecting CaCO3 precipitation, which are still debated. The implications of aragonite precipitation in the Dead Sea and in its late Pleistocene predecessor (Lake Lisan) were investigated in this study by mixing natural and synthetic brines with a synthetic bicarbonate solution that mimics flash-floods composition, with and without the addition of extracellular polymeric substances (EPS). Aragonite precipitation was monitored, and precipitation rates and carbonate yields were calculated and are discussed with respect to modern aquatic environments. The experimental insights on aragonite precipitation are then integrated with microfacies analyses in order to reconstruct and constrain prevailing limnogeological processes and their hydroclimatic drivers under low (interglacial) and high (glacial) lake level stands. Aragonite precipitation took place within days to several weeks after the mixing of the brines with a synthetic bicarbonate solution. Incubation time was proportional to bicarbonate concentration, and precipitation rates were partially influenced by ionic strength. Additionally, extracellular polymeric substances inhibited aragonite precipitation for several months. As for the lake's water budget, our calculations suggest that the precipitation of a typical aragonite lamina (0.5 mm thick) during high lake stand requires unreasonable freshwater inflow from either surface or subsurface sources. This discrepancy can be resolved by considering one or a combination of the following scenarios; (1) discontinuous aragonite deposition over parts of the lake floor; (2) supply of additional carbonate flux (or fluxes) to the lake from aeolian dust and the remobilization and dissolution of dust deposits at the watershed; (3) carbonate production via oxidation of organic carbon by sulfate-reducing bacteria. Altogether, it is suggested that aragonite laminae thickness cannot be directly interpreted for quantitatively reconstructing the hydrological balance for the entire lake, they may still prove valuable for identifying inherent hydroclimatic periodicities at a single site.
In the comment on "Varves of the Dead Sea sedimentary record." Quaternary Science Reviews 215 (Ben Dor et al., 2019): 173-184. by R. Bookman, two recently published papers are suggested to prove that the interpretation of the laminated sedimentary sequence of the Dead Sea, deposited mostly during MIS2 and Holocene pluvials, as annual deposits (i.e., varves) is wrong. In the following response, we delineate several lines of evidence which coalesce to demonstrate that based on the vast majority of evidence, including some of the evidence provided in the comment itself, the interpretation of these sediments as varves is the more likely scientific conclusion. We further discuss the evidence brought up in the comment and its irrelevance and lack of robustness for addressing the question under discussion.
The sedimentary record of the Dead Sea provides an exceptional high-resolution archive of past climate changes in the drought-sensitive eastern Mediterranean-Levant, a key region for the development of humankind at the boundary of global climate belts. Moreover, it is the only deep hypersaline lake known to have deposited long sequences of finely laminated, annually deposited sediments (i.e. varves) of varied compositions, including aragonite, gypsum, halite and clastic sediments. Vast efforts have been made over the years to decipher the environmental information stored in these evaporitic-clastic sequences spanning from the Pleistocene Lake Amora to the Holocene Dead Sea. A general characterisation of sediment facies has been derived from exposed sediment sections, as well as from shallow- and deep-water sediment cores. During high lake stands and episodes of positive water budget, mostly during glacial times, alternating aragonite and detritus laminae (‘aad’ facies) were accumulated, whereas during low lake stands and droughts, prevailing during interglacials, laminated detritus (‘ld’ facies) and laminated halite (‘lh’ facies) dominate the sequence. In this paper, we (i) review the three types of laminated sediments of the Dead Sea sedimentary record (‘aad’, ‘ld’ and ‘lh’ facies), (ii) discuss their modes of formation, deposition and accumulation, and their interpretation as varves, and (iii) illustrate how Dead Sea varves are utilized for palaeoclimate reconstructions and for establishing floating chronologies.
Assessment of climate change impact on discharge of the lakhmass catchment (Northwest Tunisia)
(2022)
The Mediterranean region is increasingly recognized as a climate change hotspot but is highly underrepresented in hydrological climate change studies. This study aims to investigate the climate change effects on the hydrology of Lakhmass catchment in Tunisia. Lakhmass catchment is a part of the Medium Valley of Medjerda in northwestern Tunisia that drains an area of 126 km(2). First, the Hydrologiska Byrans Vattenbalansavdelning light (HBV-light) model was calibrated and validated successfully at a daily time step to simulate discharge during the 1981-1986 period. The Nash Sutcliffe Efficiency and Percent bias (NSE, PBIAS) were (0.80, +2.0%) and (0.53, -9.5%) for calibration (September 1982-August 1984) and validation (September 1984-August 1986) periods, respectively. Second, HBV-light model was considered as a predictive tool to simulate discharge in a baseline period (1981-2009) and future projections using data (precipitation and temperature) from thirteen combinations of General Circulation Models (GCMs) and Regional Climatic Models (RCMs). We used two trajectories of Representative Concentration Pathways, RCP4.5 and RCP8.5, suggested by the Intergovernmental Panel on Climate Change (IPCC). Each RCP is divided into three projection periods: near-term (2010-2039), mid-term (2040-2069) and long-term (2070-2099). For both scenarios, a decrease in precipitation and discharge will be expected with an increase in air temperature and a reduction in precipitation with almost 5% for every +1 degrees C of global warming. By long-term (2070-2099) projection period, results suggested an increase in temperature with about 2.7 degrees C and 4 degrees C, and a decrease in precipitation of approximately 7.5% and 15% under RCP4.5 and RCP8.5, respectively. This will likely result in a reduction of discharge of 12.5% and 36.6% under RCP4.5 and RCP8.5, respectively. This situation calls for early climate change adaptation measures under a participatory approach, including multiple stakeholders and water users.
Subduction zone magmas are more oxidised on eruption than those at mid-ocean ridges. This is attributed either to oxidising components, derived from subducted lithosphere (slab) and added to the mantle wedge, or to oxidation processes occurring during magma ascent via differentiation. Here we provide direct evidence for contributions of oxidising slab agents to melts trapped in the sub-arc mantle. Measurements of sulfur (S) valence state in sub-arc mantle peridotites identify sulfate, both as crystalline anhydrite (CaSO4) and dissolved SO42- in spinel-hosted glass (formerly melt) inclusions. Copper-rich sulfide precipitates in the inclusions and increased Fe3+/Sigma Fe in spinel record a S6+-Fe2+ redox coupling during melt percolation through the sub-arc mantle. Sulfate-rich glass inclusions exhibit high U/Th, Pb/Ce, Sr/Nd and delta S-34 (+ 7 to + 11%), indicating the involvement of dehydration products of serpentinised slab rocks in their parental melt sources. These observations provide a link between liberated slab components and oxidised arc magmas.
The rhodolithic slope deposits of a Burdigalian carbonate platform in Sardinia near Sedini were analyzed to reconstruct facies and palaeobathymetry. There is a distinct red-algal growth zonation along the platform slope. The clinoform rollover area consists of coralline-algal bindstones, which downslope change into a zone where rhodoliths are locally fused by progressive encrustation. Mid-slope rhodoliths are moderately branched, and downslope rhodoliths have fruticose protuberances, resulting in branching rhodolith growth patterns. There is a sharp change from the rhodolitic rudstones to the basinal, bivalve-dominated rudstones at the clinoform bottomsets. Red-algal genera identified include Sporolithon, Lithophyllum, Spongites, Hydrolithon, Mesophyllum, Lithoporella, Neogoniolithon, and other mastophoroids and melobesioids. Genera and subfamilies show a zonation along the clinoforms, allowing palaeobathymetric estimates. The clinoform rollovers formed at a water depth of around 40 m and the bottomsets around 60 m. Results from geometrical reconstruction show that coral reefs in the inner platform formed at water depths of around 20 m. Therefore, the Sedini carbonate platform is an example of a reef-bearing platform in which the edge or the platform-interior reefs do not build up to sea level.
The aim of this paper is to estimate the Hurst parameter of Fractional Gaussian Noise (FGN) using Bayesian inference. We propose an estimation technique that takes into account the full correlation structure of this process. Instead of using the integrated time series and then applying an estimator for its Hurst exponent, we propose to use the noise signal directly. As an application we analyze the time series of the Nile River, where we find a posterior distribution which is compatible with previous findings. In addition, our technique provides natural error bars for the Hurst exponent.
The displacement histories of the San Jacinto and southernmost San Andreas fault zones are constrained by offset data with ages in the range of 5 Ma to 5 ka. Apparent discrepancies between long- and short-term average displacement rates can be reconciled with a time-variable rate model. In this model, the displacement rate on the San Andreas decelerated from similar to35 mm/yr at 1.5 Ma to as low as 9 +/- 4 mm/yr by 90 ka. Over this same time period, the rate on the San Jacinto fault zone accelerated from an initial value of zero to a rate of 26 +/- 4 mm/yr. The data also imply that the rate of the San Andreas fault accelerated since ca. 90 ka, from similar to9 mm/yr to the modern rate of 27 +/- 4 mm/yr, whereas the San Jacinto decelerated from 26 +/- 4 mm/yr to the modern rate of 8 +/- 4 mm/yr. The time scale of these changes is significantly longer than the earthquake cycle, but shorter than time scales characteristic of lithospheric-scalle dynamics. The emergence of the San Jacinto fault zone ca. 1.5 Ma coincided with the development of a major restraining bend in the San Andreas fault zone, suggesting that the formation of new subparallell faults could be driven by conditions that inhibit displacement on preexisting faults
Analysis of past and present stimulation projects reveals that the temporal evolution and growth of maximum observed moment magnitudes may be linked directly to the injected fluid volume and hydraulic energy. Overall evolution of seismic moment seems independent of the tectonic stress regime and is most likely governed by reservoir specific parameters, such as the preexisting structural inventory. Data suggest that magnitudes can grow either in a stable way, indicating the constant propagation of self-arrested ruptures, or unbound, for which the maximum magnitude is only limited by the size of tectonic faults and fault connectivity. Transition between the two states may occur at any time during injection or not at all. Monitoring and traffic light systems used during stimulations need to account for the possibility of unstable rupture propagation from the very beginning of injection by observing the entire seismicity evolution in near-real time and at high resolution for an immediate reaction in injection strategy.
Plain Language Summary Predicting and controlling the size of earthquakes caused by fluid injection is currently the major concern of many projects associated with geothermal energy production. Here, we analyze the magnitude and seismic moment evolution with injection parameters for prominent geothermal and scientific projects to date. Evolution of seismicity seems to be largely independent of the tectonic stress background and seemingly depends on reservoir specific characteristics. We find that the maximum observed magnitudes relate linearly to the injected volume or hydraulic energy. A linear relation suggests stable growth of induced ruptures, as predicted by current models, or rupture growth may no longer depend on the stimulated volume but on tectonics. A system may change between the two states during the course of fluid injection. Close-by and high-resolution monitoring of seismic and hydraulic parameters in near-real time may help identify these fundamental changes in ample time to change injection strategy and manage maximum magnitudes.
Preparatory mechanisms accompanying or leading to nucleation of larger earthquakes have been observed at both laboratory and field scales, but conditions favoring the occurrence of observable preparatory processes are still largely unknown. In particular, it remains a matter of debate why some earthquakes occur spontaneously without noticeable precursors as opposed to events that are preceded by an extended failure process. In this study, we have generated new high-resolution seismicity catalogs framing the occurrence of 20 M-L > 2.5 earthquakes at The Geysers geothermal field in California. To this end, a seismicity catalog of the 11 days framing each large event was created. We selected 20 sequences sampling different hypocentral depths and hydraulic conditions within the field. Seismic activity and magnitude frequency distributions displayed by the different earthquake sequences are correlated with their location within the reservoir. Sequences located in the northwestern part of the reservoir show overall increased seismic activity and low b values, while the southeastern part is dominated by decreased seismic activity and higher b values. Periods of high injection coincide with high b values and vice versa. These observations potentially reflect varying differential and mean stresses and damage of the reservoir rocks across the field. About 50% of analyzed sequences exhibit no change in seismicity rate in response to the large main event. However, we find complex waveforms at the onset of the main earthquake, suggesting that small ruptures spontaneously grow into or trigger larger events.
Oxygen (O-2) availability in soils is vital for plant growth and productivity. The transport and consumption of O-2 in the root zone is closely linked to soil moisture content, the spatial distribution of roots, as well as structure and heterogeneity of the surrounding soil. In this study, we measure three-dimensional root system architecture and the spatiotemporal dynamics of soil moisture (& theta;) and O-2 concentrations in the root zone of maize (Zea mays) via non-invasive imaging, and then construct and parameterize a reactive transport model based on the experimental data. The combination of three non-invasive imaging methods allowed for a direct comparison of simulation results with observations at high spatial and temporal resolution. In three different modeling scenarios, we investigated how the results obtained for different levels of conceptual complexity in the model were able to match measured & theta; and O-2 concentration patterns. We found that the modeling scenario that considers heterogeneous soil structure and spatial variability of hydraulic parameters (permeability, porosity, and van Genuchten & alpha; and n), better reproduced the measured & theta; and O-2 patterns relative to a simple model with a homogenous soil domain. The results from our combined imaging and modeling analysis reveal that experimental O-2 and water dynamics can be reproduced quantitatively in a reactive transport model, and that O-2 and water dynamics are best characterized when conditions unique to the specific system beyond the distribution of roots, such as soil structure and its effect on water saturation and macroscopic gas transport pathways, are considered.
Tectonic and metamorphic data for the Central Alps (Switzerland/Italy) are used to discuss this classic example of a Barrovian metamorphic terrain, notably the evolution of its thermal structure in space and time. Available P-T-t data indicate variable contributions of advective and conductive heat transport during collision and subsequent cooling and exhumation. Some areas experienced a prolonged period of partial melting while other areas, at the same time, show but moderate heating. The Barrow-type metamorphic field gradient observed in the final orogen is the result of two distinct tectonic processes, with their related advective and conductive heat transport processes. The two tectonic processes are (1) accretion of material within a subduction channel related to decompression and emplacement of high-pressure units in the middle crust and (2) wedging and related nappe formation in the continental lower plate. The second process postdates the first one. Wedging and underthrusting of continental lower plate material produces heat input into lower crustal levels, and this process is responsible for predominantly conductive heat transport in the overlying units. The interacting processes lead to different maximum temperatures at different times, producing the final Barrovian metamorphic field gradient. The south experienced rapid cooling, whereas the north shows moderate cooling rates. This discrepancy principally reflects differences in the temperature distribution in the deeper crust prior to cooling. Differences in the local thermal gradient that prevailed before the cooling also determined the relationships between cooling rate and exhumation rate in the different areas. Citation: Berger, A., S. M. Schmid, M. Engi, R. Bousquet, and M. Wiederkehr (2011), Mechanisms of mass and heat transport during Barrovian metamorphism: A discussion based on field evidence from the Central Alps (Switzerland/northern Italy), Tectonics, 30, TC1007, doi:10.1029/2009TC002622.
In this work, an approach of paleoclimate reconstruction for tropical East Africa is presented. After giving a short summary of modern climate conditions in the tropics and the East African climate peculiarity, the potential of reconstructing climate from paleolake sediments is discussed. As demonstrated, the hydrologic sensitivity of high-elevated closed-basin lakes in the Central Kenya Rift yields valuable guaranties for the establishment of long-term climate records. Temporal fluctuations of the limnological characteristics saved in the lake sediments are used to define variations in the Quaternary climate history. Based on diatom analyses in radiocarbon- and 40Ar/39Ar-dated sediments, a chronology of paleoecologic fluctuations is developed for the Central Kenya Rift -lakes Nakuru, Elmenteita and Naivasha. At least during the penultimate interglacial (around 140 to 60 kyr BP) and during the last interglacial (around 12 to 4 kyr BP), these lakes experienced several transgression-regression cycles on time intervals of about 11,000 years. Additionally, a long-term trend of lake evolution is found suggesting the general succession from deep freshwater lakes towards more saline waters during the last million years. Using ecologic transfer functions and a simple lake-balance model, the observed paleohydrologic fluctuations are linked to potential precipitation-evaporation changes in the lake basins. Though also tectonic influences on the drainage pattern and the effect of varied seepage are investigated, it can be shown that already a small increase in precipitation of about 30±10 % may have affected the hydrologic budget of the intra-rift lakes within the reconstructed range. The findings of this study help to assess the natural climate variability of East Africa. They furthermore reflect the sensitivity of the Central Kenya Rift -lakes to fluctuations of large-scale climate parameters, such as solar radiation and sea-surface temperatures of the Indian Ocean.
Tectonic and climatic control on evolution of rift lakes in the Central Kenya Rift, East Africa
(2009)
The long-term histories of the neighboring Nakuru-Elmenteita and Naivasha lake basins in the Central Kenya Rift illustrate the relative importance of tectonic versus climatic effects on rift-lake evolution and the formation of disparate sedimentary environments. Although modem climate conditions in the Central Kenya Rift are very similar for these basins, hydrology and hydrochemistry of present-day lakes Nakuru, Elmenteita and Naivasha contrast dramatically due to tectonically controlled differences in basin geometries, catchment size, and fluvial processes. In this study, we use eighteen C-14 and Ar-40/Ar-39 dated fluvio-lacustrine sedimentary sections to unravel the spatiotemporal evolution of the lake basins in response to tectonic and climatic influences. We reconstruct paleoclimatic and ecological trends recorded in these basins based on fossil diatom assemblages and geologic field mapping. Our study shows a tendency towards increasing alkalinity and shrinkage of water bodies in both lake basins during the last million years. Ongoing volcano-tectonic segmentation of the lake basins, as well as reorganization of upstream drainage networks have led to contrasting hydrologic regimes with adjacent alkaline and freshwater conditions. During extreme wet periods in the past, such as during the early Holocene climate optimum, lake levels were high and all basins evolved toward freshwater systems. During drier periods some of these lakes revert back to alkaline conditions, while others maintain freshwater characteristics. Our results have important implications for the use and interpretation of lake sediment as climate archives in tectonically active regions and emphasize the need to deconvolve lacustrine records with respect to tectonics versus climatic forcing mechanisms.
Three diatomite beds exposed in the Ol Njorowa Gorge south of Lake Naivasha, Central Kenya Rift, document three major lake-level highstands between 175 and 60 kyr BP. Diatom transfer-function estimates of hydrological and hydrochemical parameters suggest that a deep and large freshwater lake existed during the highstands at 135 and 80 kyr BP. In contrast, a shallower but more expanded freshwater lake existed at 110 kyr BP. The best analog for the most extreme highstand at 135 kyr BP is the highstand during the Early Holocene humid period from 10 to 6 kyr BP. The environmental conditions as reconstructed from diatom assemblages suggest long-lasting episodes of increased humidity during the high lake periods. This contrasts to the modern situation with a relatively shallow Lake Naivasha characterized by rapid water level fluctuations within a few decades. The most likely cause for the variable hydrological conditions since 175 kyr BP is orbitally driven insolation changes on the equator and increased lateral moisture transport from the ocean.
We modeled the two most extreme highstands of Lake Naivasha during the last 175 k.y. to estimate potential precipitation/ evaporation changes in this basin. In a first step, the bathymetry of the paleolakes at f135 and 9 k.y. BP was reconstructed from sediment cores and surface outcrops. Second, we modeled the paleohydrologic budget during the highstands using a simplified coupled energy mass-balance model. Our results show that the hydrologic and hence the climate conditions at f135 and 9 k.y. BP were similar, but significantly different from today. The main difference is a f15% higher value in precipitation compared to the present. An adaptation and migration of vegetation in the cause of climate changes would result in a f30% increase in precipitation. The most likely cause for such a wetter climate at f135 and 9 k.y. BP is a more intense intertropical convergence and increased precipitation in East Africa.
Three spinel lherzolite xenoliths from Mt. Quincan (Queensland, northeastern Australia) were studied with special attention to their enclosed fluid inclusions. The xenoliths are deformed, have porphyroclastic textures and overall show very similar petrographic features. The only significant difference is manifested in the abundance of fluid inclusions in the samples, mostly in orthopyroxene porphyroclasts. Xenolith JMTQ11 is fluid inclusion-free, whereas xenolith JMTQ20 shows a high abundance of fluid inclusions (fluid inclusion-rich). Xenolith JMTQ45 represents a transitional state between the previous two, as it contains only a small amount of fluid inclusions (fluid inclusion-bearing). Previous studies revealed that these xenoliths and the entrapped fluid inclusions represent a former addition of a MORB-type fluid to the pre-existing lithosphere, resulting from asthenosphere upwelling. There is a progressive enrichment in LREE, Nb, Sr and Ti from the fluid inclusion-free xenolith through the fluid inclusion-bearing one to the fluid inclusion-rich lherzolite. This suggests an increase in the extent of the interaction between the fluid-rich melt and the lherzolite wallrock. In addition, the same interaction is considered to be responsible for the formation of pargasitic amphibole as well. The presence of fluid inclusions indicates fluid migration at mantle depth, and their association with exsolution lamellae in orthopyroxene suggests fluid entrapment following the continental rifting (thermal relaxation) during cooling. A series of analyses, including microthermometry coupled with Raman spectroscopy, FTIR hyperspectral imaging, and Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) was carried out on the fluid inclusions. Based on the results, the entrapped high-density fluid is composed of 7589 mol% CO2, 918 mol% H2O, 0.11.7 mol% N-2 and <= 0.5 mol% H2S with dissolved trace elements (melt component). Our findings suggest that the metasomatic fluid phase could have been either a fluid/fluid-rich silicate melt released from the deeper asthenosphere, or a coexisting incipient fluid-rich silicate melt. Further cooling, possibly due to thermal relaxation and the upward migration of the fluid phase, caused the investigated lherzolites to reach pargasite stability conditions. We conclude that pargasite, even if only present in very limited modal proportions, can be a common phase at spinel lherzolite stability in the lithospheric upper mantle in continental rift back-arc settings. Studies of fluid inclusions indicate that significant CO2 release from the asthenosphere in a continental rifting environment is resulting from asthenosphere upwelling and its addition to the lithospheric mantle together with fluid-rich melt lherzolite interaction that leaves a CO2-rich fluid behind.
Scarce research about small European rivers from non-human impacted areas to determine their natural background state has been undertaken. During the annual hydrological cycle of 2008-9 the patterns of particulate supply (SPM, POC, PON, Al, Cd, Co, Cr, Cu, Fe, Ni, Pb, V, Zn) from the rivers Sor, Mera Landro, Lourido and Landoi to the Northern Galician Rias (SW Bay of Biscay) were tackled. No differences in the composition of the SPM were detected for the studied rivers regarding Al, Fe and POC but the relative percentage of particulate trace elements (PTE) discriminate the rivers. So, Cr, Co and Ni in the Lourido, and Landoi rivers, and Cu in the Mera River, are controlled by watershed minerals of Ortegal Geological Complex while for the rest rivers PTE are by granitic and Ollo de Sapo bedrock watershed. Therefore, the imprint of PTE in the parental rocks of the river basins is reflected on the coastal sediments of the Rias. The main process controlling the dynamics and variations of chemical elements in the particulate form is the river discharge. This fact exemplifies that these rivers presents a natural behavior not being highly influenced by anthropogenic activities.
During the last 5 Ma the Earth's ocean-atmosphere system passed through several major transitions, many of which are discussed as possible triggers for human evolution. A classic in this context is the possible influence of the closure of the Panama Strait, the intensification of Northern Hemisphere Glaciation, a stepwise increase in aridity in Africa, and the first appearance of the genus Homo about 2.5 - 2.7 Ma ago. Apart from the fact that the correlation between these events does not necessarily imply causality, many attempts to establish a relationship between climate and evolution fail due to the challenge of precisely localizing an a priori unknown number of changes potentially underlying complex climate records. The kernel-based Bayesian inference approach applied here allows inferring the location, generic shape, and temporal scale of multiple transitions in established records of Plio-Pleistocene African climate. By defining a transparent probabilistic analysis strategy, we are able to identify conjoint changes occurring across the investigated terrigenous dust records from Ocean Drilling Programme (ODP) sites in the Atlantic Ocean (ODP 659), Arabian (ODP 721/722) and Mediterranean Sea (ODP 967). The study indicates a two-step transition in the African climate proxy records at (2.35-2.10) Ma and (1.70 - 1.50) Ma, that may be associated with the reorganization of the Hadley-Walker Circulation. .