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Clusty is a new open source toolbox dedicated to earthquake clustering based on waveforms recorded across a network of seismic stations. Its main application is the study of active faults and the detection and characterization of faults and fault networks. By using a density-based clustering approach, earthquakes pertaining to a common fault can be recognized even over long fault segments, and the first-order geometry and extent of active faults can be inferred. Clusty implements multiple techniques to compute a waveform based network similarity from maximum cross-correlation coefficients at multiple stations. The clustering procedure is designed to be transparent and parameters can be easily tuned. It is supported by a number of analysis visualization tools which help to assess the homogeneity within each cluster and the differences among distinct clusters. The toolbox returns graphical representations of the results. A list of representative events and stacked waveforms facilitate further analyses like moment tensor inversion. Results obtained in various frequency bands can be combined to account for large magnitude ranges. Thanks to the simple configuration, the toolbox is easily adaptable to new data sets and to large magnitude ranges. To show the potential of our new toolbox, we apply Clusty to the aftershock sequence of the M-w 6.9 25 October 2018 Zakynthos (Greece) Earthquake. Thanks to the complex tectonic setting at the western termination of the Hellenic Subduction System where multiple faults and faulting styles operate simultaneously, the Zakynthos data set provides an ideal case-study for our clustering analysis toolbox. Our results support the activation of several faults and provide insight into the geometry of faults or fault segments. We identify two large thrust faulting clusters in the vicinity of the main shock and multiple strike-slip clusters to the east, west and south of these clusters. Despite its location within the largest thrust cluster, the main shock does not show a high waveform similarity to any of the clusters. This is consistent with the results of other studies suggesting a complex failure mechanism for the main shock. We propose the existence of conjugated strike-slip faults in the south of the study area. Our waveform similarity based clustering toolbox is able to reveal distinct event clusters which cannot be discriminated based on locations and/or timing only. Additionally, the clustering results allows distinction between fault and auxiliary planes of focal mechanisms and to associate them to known active faults.
Impact of Late Pleistocene climate variability on paleo-erosion rates in the western Himalaya
(2022)
It has been proposed that at short timescales of 10(2)-10(5) yr, climatic variability can explain variations in sediment flux, but in orogens with pronounced climatic gradients rate changes caused by the oscillating efficiency in rainfall, runoff, and/or sediment transport and deposition are still not well-constrained.
To explore landscape responses under variable climatic forcing, we evaluate time windows of prevailing sediment aggradation and related paleo-erosion rates from the southern flanks of the Dhauladhar Range in the western Himalaya.
We compare past and present Be-10-derived erosion rates of well-dated Late Pleistocene fluvial landforms and modern river sediments and reconstruct the sediment aggradation and incision history based on new luminescence data.
Our results document significant variations in erosion rates ranging from 0.1 to 3.4 mm/yr over the Late Pleistocene.
We find that, during times of weak monsoon intensity, the moderately steep areas (hillslope angles of 27 +/- 13 degrees) erode at lower rates of 0.1-0.4 mm/yr compared to steeper (>40 degrees) crestal regions of the Dhauladhar Range that erode at 0.8-1.3 mm/yr.
In contrast, during several millennia of stronger monsoon intensity, both the moderately steep and high slope areas record higher erosion rates (>1-3.4 mm/yr). Lithological clast-count analysis shows that this increase of erosion is focused in the moderately steep areas, where Lesser Himalayan rocks are exposed.
Our data thus highlight the highly non-linear response of climatic forcing on landscape evolution and suggest complex depositional processes and sedimentary signals in downstream areas. (C) 2021 Elsevier B.V. All rights reserved.
Bastnsite [REE(CO3)F] is the main mineral of REE ore deposits in carbonatites. Synthetic bastnsite-like compounds were precipitated from aqueous solutions by many different methods, but previous attempts to model magmatic crystallization of bastnsite from hydrous calciocarbonatite melts were unsuccessful.
Here we present the first experimental evidence that bastnsite and two other REE carbonates, burbankite, and lukechangite, can crystallize from carbonatite melt in the synthetic system La(CO3)F-CaCO3-Na2CO3 at temperatures between 580 and 850 degrees C and a pressure 100 MPa.
The experiments on starting mixtures of reagent-grade CaCO3, Na2CO3, La-2(CO3)(3), and LaF3 were carried out in cold-seal rapid-quench pressure vessels.
The studied system is an isobaric pseudoternary join of a quinary system where CO2 and fluorides act as independent components. Liquidus phases in the run products are calcite, nyerereite, Na carbonate, bastnsite, burbankite solid solution (Na,Ca)(3)(Ca,La)(3)(CO3)(5), and lukechangite Na3La2(CO3)(4)F. Calcite and bastnite form a eutectic in the boundary join La(CO3)F-CaCO3 at 780 +/- 20 degrees C and 58 wt% La(CO3)F. Phase equilibria in the boundary join La(CO3)F-Na2CO3 are complicated by peritectic reaction between Ca-free end-member of burbankite solid solution petersenite (Pet) and lukechangite (Luk) with liquid (L): Na4La2(CO3)(5) (Pet) + NaF (L) = Na3La2(CO3)(4)F (Luk) + Na2CO3 (Nc).
The right-hand-side assemblage becomes stable below 600 +/- 20 degrees C. In ternary mixtures, bastnsite (Bst), burbankite (Bur), and calcite (Cc) are involved in another peritectic reaction: 2La(CO3)F (Bst) + CaCO3 (Cc) + 2Na(2)CO(3) (L) = Na2CaLa2(CO3)(5) (Bur) + 2NaF (L). Burbankite in equilibrium with calcite replaces bastnsite below 730 +/- 20 degrees C. Stable solidus assemblages in the pseudoternary system are: basnsite-burbankite-fluorite-calcite, basnasite-burbankite-fluorite-lukechangite, bastnsite-burbankite-lukechangite, burbankite-lukechangite-nyerereitecalcite, and burbankite-lukechangite-nyerereite-natrite. Addition of 10 wt% Ca-3(PO4)(2) to one of the ternary mixtures resulted in massive crystallization of La-bearing apatite and monazite and complete disappearance of bastnsite and burbankite.
Our results confirm that REE-bearing phosphates are much more stable than carbonates and fluorocarbonates.
Therefore, primary crystallization of the latter from common carbonatite magmas is unlikely. Possible exceptions are carbonatites at Mountain Pass that are characterized by very low P2O5 concentrations (usually at or below 0.5 wt%) and extremely high REE contents in the order of a few weight percent or more. In other carbonatites, bastnsite and burbankite probably crystallized from highly concentrated alkaline carbonate-chloride brines that were found in melt inclusions and are thought to be responsible for widespread fenitization around carbonatite bodies.
The chaotic spatio-temporal electrical activity during life-threatening cardiac arrhythmias like ventricular fibrillation is governed by the dynamics of vortex-like spiral or scroll waves. The organizing centers of these waves are called wave tips (2D) or filaments (3D) and they play a key role in understanding and controlling the complex and chaotic electrical dynamics. Therefore, in many experimental and numerical setups it is required to detect the tips of the observed spiral waves. Most of the currently used methods significantly suffer from the influence of noise and are often adjusted to a specific situation (e.g. a specific numerical cardiac cell model). In this study, we use a specific type of deep neural networks (UNet), for detecting spiral wave tips and show that this approach is robust against the influence of intermediate noise levels. Furthermore, we demonstrate that if the UNet is trained with a pool of numerical cell models, spiral wave tips in unknown cell models can also be detected reliably, suggesting that the UNet can in some sense learn the concept of spiral wave tips in a general way, and thus could also be used in experimental situations in the future (ex-vivo, cell-culture or optogenetic experiments).
From June to August 2021, we deployed a dense seismic nodal network across the Hengill geothermal area in southwest Iceland to image and characterize faults and high-temperature zones at high resolution.
The nodal network comprised 498 geophone nodes spread across the northern Nesjavellir and southern Hverahlio geothermal fields and was complemented by an existing permanent and temporary backbone seismic network of a total of 44 short-period and broadband stations.
In addition, we recorded distributed acoustic sensing data along two fiber optic telecommunication cables near the Nesjavellir geothermal power plant with commercial interrogators.
During the time of deployment, a vibroseis survey took place around the Nesjavellir power plant.
Here, we describe the network and the recorded datasets.
Furthermore, we showsome initial results that indicate a high data quality and highlight the potential of the seismic records for various follow up studies, such as high-resolution event location to delineate faults and body- and surface-wave tomographies to image the subsurface velocity structure in great detail.
Lakes act as important sinks for inorganic and organic sediment components. However, investigations of sedimentary carbon budgets within glacial lakes are currently absent from Arctic Siberia. The aim of this paper is to provide the first reconstruction of accumulation rates, sediment and carbon budgets from a lacustrine sediment core from Lake Rauchuagytgyn, Chukotka (Arctic Siberia). We combined multiple sediment biogeochemical and sedimentological parameters from a radiocarbon-dated 6.5m sediment core with lake basin hydroacoustic data to derive sediment stratigraphy, sediment volumes and infill budgets. Our results distinguished three principal sediment and carbon accumulation regimes that could be identified across all measured environmental proxies including early Marine Isotope Stage 2 (MIS2) (ca. 29-23.4 ka cal BP), mid-MIS2-early MIS1 (ca. 23.4-11.69 ka cal BP) and the Holocene (ca. 11.69-present). Estimated organic carbon accumulation rates (OCARs) were higher within Holocene sediments (average 3.53 gOCm(-2) a(-1)) than Pleistocene sediments (average 1.08 gOCm(-2) a(-1)) and are similar to those calculated for boreal lakes from Quebec and Finland and Lake Baikal but significantly lower than Siberian thermokarst lakes and Alberta glacial lakes. Using a bootstrapping approach, we estimated the total organic carbon pool to be 0.26 +/- 0.02 Mt and a total sediment pool of 25.7 +/- 1.71 Mt within a hydroacoustically derived sediment volume of ca. 32 990 557m(3). The total organic carbon pool is substantially smaller than Alaskan yedoma, thermokarst lake sediments and Alberta glacial lakes but shares similarities with Finnish boreal lakes. Temporal variability in sediment and carbon accumulation dynamics at Lake Rauchuagytgyn is controlled predominantly by palaeoclimate variation that regulates lake ice-cover dynamics and catchment glacial, fluvial and permafrost processes through time. These processes, in turn, affect catchment and within-lake primary productivity as well as catchment soil development. Spatial differences compared to other lake systems at a trans-regional scale likely relate to the high-latitude, mountainous location of Lake Rauchuagytgyn.
Martian atmospheric spectral end-members retrieval from ExoMars Thermal Infrared (TIRVIM) data
(2022)
Key knowledge about planetary composition can be recovered from the study of thermal infrared spectral range datasets.
This range has a huge diagnostic potential because it contains diagnostic absorptions from a planetary surface and atmosphere. The main goal of this study is to process and interpret the dataset from the Thermal Infrared channel (TIRVIM) which is part of the Atmospheric Chemistry Suite of the ExoMars2016 Trace Gas Orbiter mission to find and characterize dust and water ice clouds in the atmosphere.
The method employed here is based on the application of principal component analysis and target transformation techniques to extract the independent variable components present in the analyzed dataset. Spectral shapes of both atmospheric dust and water ice aerosols have been recovered from the analysis of TIRVIM data.
The comparison between our results with those previously obtained on Thermal Emission Spectrometer (TES) data and with previous analysis on TIRVIM data, validates the methodology here applied, showing that it allows to correctly recover the atmospheric spectral endmembers present in the TIRVIM data.
Moreover, comparison with atmospheric retrievals on PFS, TES and IRIS data, allowed us to assess the temporal stability and homogeneity of dust and water ice components in the Martian atmosphere over a time period of almost 50 years.
The early exhumation history of the Tauern Window in the European Eastern Alps and its surface expression is poorly dated and quantified, partly because thermochronological and provenance information are sparse from the Upper Austrian Northern Alpine Foreland Basin. For the first time, we combine a single-grain double-dating approach (Apatite Fission Track and U-Pb dating) with trace-element geochemistry analysis on the same apatites to reconstruct the provenance and exhumation history of the late Oligocene/early Miocene Eastern Alps. The results from 22 samples from the Chattian to Burdigalian sedimentary infill of the Upper Austrian Northern Alpine Foreland Basin were integrated with a 3D seismic-reflection data set and published stratigraphic reports. Our highly discriminative data set indicates an increasing proportion of apatites (from 6% to 23%) with Sr/Y values <0.1 up-section and an increasing amount of apatites (from 24% to 38%) containing >1,000 ppm light rare-earth elements from Chattian to Burdigalian time. The number of U-Pb ages with acceptable uncertainties increases from 40% to 59% up-section, with mostly late Variscan/Permian ages, while an increasing number of grains (10%-27%) have Eocene or younger apatite fission track cooling ages. The changes in the apatite trace-element geochemistry and U-Pb data mirror increased sediment input from an >= upper amphibolite-facies metamorphic source of late Variscan/Permian age - probably the otztal-Bundschuh nappe system - accompanied by increasing exhumation rates indicated by decreasing apatite fission track lag times. We attribute these changes to the surface response to upright folding and doming in the Penninic units of the future Tauern Window starting at 29-27 Ma. This early period of exhumation (0.3-0.6 mm/a) is triggered by early Adriatic indentation along the Giudicarie Fault System.
Natural gas can be temporarily stored in a variety of underground facilities, such as depleted gas and oil fields, natural aquifers and caverns in salt rocks. Being extensively monitored during operations, these systems provide a favourable opportunity to investigate how pressure varies in time and space and possibly induces/triggers earthquakes on nearby faults. Elaborate and detailed numerical modelling techniques are often applied to study gas reservoirs. Here we show the possibilities and discuss the limitations of a flexible and easily formulated tool that can be straightforwardly applied to simulate temporal pore-pressure variations and study the relation with recorded microseismic events. We use the software POEL (POroELastic diffusion and deformation) which computes the poroelastic response to fluid injection/extraction in a horizontally layered poroelastic structure. We further develop its application to address the presence of vertical impermeable faults bounding the reservoir and of multiple injection/extraction sources. Exploiting available information on the reservoir geometry and physical parameters, and records of injection/extraction rates for a gas reservoir in southern Europe, we perform an extensive parametric study considering different model configurations. Comparing modelled spatiotemporal pore-pressure variations with in situ measurements, we show that the inclusion of vertical impermeable faults provides an improvement in reproducing the observations and results in pore-pressure accumulation near the faults and in a variation of the temporal pore-pressure diffusion pattern. To study the relation between gas storage activity and recorded local microseismicity, we applied different seismicity models based on the estimated porepressure distribution. This analysis helps to understand the spatial distribution of seismicity and its temporal modulation. The results show that the observed microseismicity could be partly linked to the storage activity, but the contribution of tectonic background seismicity cannot be excluded.
Reservoir-triggered seismicity has been observed near dams during construction, impoundment, and cyclic filling in many parts of the earth. In Turkey, the number of dams has increased substantially over the last decade, with Ataturk Dam being the largest dam in Turkey with a total water capacity of 48.7 billion m(3). After the construction of the dam, the monitoring network has improved. Considering earthquakes above the long-term completeness magnitude of M-C = 3.5, the local seismicity rate has substantially increased after the filling of the reservoir. Recently, two damaging earthquakes of M-w 5.5 and M-w 5.1 occurred in the town of Samsat near the Ataturk Reservoir in 2017 and 2018, respectively. In this study, we analyze the spatio-temporal evolution of seismicity and its source properties in relation to the temporal water-level variations and the stresses resulting from surface loading and pore-pressure diffusion. We find that water-level and seismicity rate are anti-correlated, which is explained by the stabilization effect of the gravitational induced stress imposed by water loading on the local faults. On the other hand, we find that the overall effective stress in the seismogenic zone increased over decades due to pore-pressure diffusion, explaining the enhanced background seismicity during recent years. Additionally, we observe a progressive decrease of the Gutenberg-Richter b-value. Our results indicate that the stressing rate finally focused on the region where the two damaging earthquakes occurred in 2017 and 2018.