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Understanding the relation between injection-induced seismic moment release and operational parameters is crucial for early identification of possible seismic hazards associated with fluid-injection projects. We conducted laboratory fluid-injection experiments on permeable sandstone samples containing a critically stressed fault at different fluid pressurization rates. The observed fluid-induced fault deformation is dominantly aseismic. Fluid-induced stick-slip and fault creep reveal that total seismic moment release of acoustic emission (AE) events is related to total injected volume, independent of respective fault slip behavior. Seismic moment release rate of AE scales with measured fault slip velocity. For injection-induced fault slip in a homogeneous pressurized region, released moment shows a linear scaling with injected volume for stable slip (steady slip and fault creep), while we find a cubic relation for dynamic slip. Our results highlight that monitoring evolution of seismic moment release with injected volume in some cases may assist in discriminating between stable slip and unstable runaway ruptures.
To find out the future of nowadays reef ecosystem turnover under the environmental stresses such as global warming and ocean acidification, analogue studies from the geologic past are needed. As a critical time of reef ecosystem innovation, the Permian-Triassic transition witnessed the most severe demise of Phanerozoic reef builders, and the establishment of modern style symbiotic relationships within the reef-building organisms. Being the initial stage of this transition, the Middle Permian (Capitanian) mass extinction coursed a reef eclipse in the early Late Permian, which lead to a gap of understanding in the post-extinction Wuchiapingian reef ecosystem, shortly before the radiation of Changhsingian reefs. Here, this thesis presents detailed biostratigraphic, sedimentological, and palaeoecological studies of the Wuchiapingian reef recovery following the Middle Permian (Capitanian) mass extinction, on the only recorded Wuchiapingian reef setting, outcropping in South China at the Tieqiao section.
Conodont biostratigraphic zonations were revised from the Early Permian Artinskian to the Late Permian Wuchiapingian in the Tieqiao section. Twenty main and seven subordinate conodont zones are determined at Tieqiao section including two conodont zone below and above the Tieqiao reef complex. The age of Tieqiao reef was constrained as early to middle Wuchiapingian.
After constraining the reef age, detailed two-dimensional outcrop mapping combined with lithofacies study were carried out on the Wuchiapingian Tieqiao Section to investigate the reef growth pattern stratigraphically as well as the lateral changes of reef geometry on the outcrop scale. Semi-quantitative studies of the reef-building organisms were used to find out their evolution pattern within the reef recovery. Six reef growth cycles were determined within six transgressive-regressive cycles in the Tieqiao section. The reefs developed within the upper part of each regressive phase and were dominated by different biotas. The timing of initial reef recovery after the Middle Permian (Capitanian) mass extinction was updated to the Clarkina leveni conodont zone, which is earlier than previous understanding. Metazoans such as sponges were not the major components of the Wuchiapingian reefs until the 5th and 6th cycles. So, the recovery of metazoan reef ecosystem after the Middle Permian (Capitanian) mass extinction was obviously delayed. In addition, although the importance of metazoan reef builders such as sponges did increase following the recovery process, encrusting organisms such as Archaeolithoporella and Tubiphytes, combined with microbial carbonate precipitation, still played significant roles to the reef building process and reef recovery after the mass extinction.
Based on the results from outcrop mapping and sedimentological studies, quantitative composition analysis of the Tieqiao reef complex were applied on selected thin sections to further investigate the functioning of reef building components and the reef evolution after the Middle Permian (Capitanian) mass extinction. Data sets of skeletal grains and whole rock components were analyzed. The results show eleven biocommunity clusters/eight rock composition clusters dominated by different skeletal grains/rock components. Sponges, Archaeolithoporella and Tubiphytes were the most ecologically important components within the Wuchiapingian Tieqiao reef, while the clotted micrites and syndepositional cements are the additional important rock components for reef cores. The sponges were important within the whole reef recovery. Tubiphytes were broadly distributed in different environments and played a key-role in the initial reef communities. Archaeolithoporella concentrated in the shallower part of reef cycles (i.e., the upper part of reef core) and was functionally significant for the enlargement of reef volume.
In general, the reef recovery after the Middle Permian (Capitanian) mass extinction has some similarities with the reef recovery following the end-Permian mass extinction. It shows a delayed recovery of metazoan reefs and a stepwise recovery pattern that was controlled by both ecological and environmental factors. The importance of encrusting organisms and microbial carbonates are also similar to most of the other post-extinction reef ecosystems. These findings can be instructive to extend our understanding of the reef ecosystem evolution under environmental perturbation or stresses.
A ground motion logic tree for seismic hazard analysis in the stable cratonic region of Europe
(2020)
Regions of low seismicity present a particular challenge for probabilistic seismic hazard analysis when identifying suitable ground motion models (GMMs) and quantifying their epistemic uncertainty. The 2020 European Seismic Hazard Model adopts a scaled backbone approach to characterise this uncertainty for shallow seismicity in Europe, incorporating region-to-region source and attenuation variability based on European strong motion data. This approach, however, may not be suited to stable cratonic region of northeastern Europe (encompassing Finland, Sweden and the Baltic countries), where exploration of various global geophysical datasets reveals that its crustal properties are distinctly different from the rest of Europe, and are instead more closely represented by those of the Central and Eastern United States. Building upon the suite of models developed by the recent NGA East project, we construct a new scaled backbone ground motion model and calibrate its corresponding epistemic uncertainties. The resulting logic tree is shown to provide comparable hazard outcomes to the epistemic uncertainty modelling strategy adopted for the Eastern United States, despite the different approaches taken. Comparison with previous GMM selections for northeastern Europe, however, highlights key differences in short period accelerations resulting from new assumptions regarding the characteristics of the reference rock and its influence on site amplification.
Probabilistic assessment of seismic hazard and risk over a geographical region presents the modeler with challenges in the characterization of the site amplification that are not present in site-specific assessment. Using site-to-site residuals from a ground motion model fit to observations from the Japanese KiK-net database, correlations between measured local amplifications and mappable proxies such as topographic slope and geology are explored. These are used subsequently to develop empirical models describing amplification as a direct function of slope, conditional upon geological period. These correlations also demonstrate the limitations of inferring 30-m shearwave velocity from slope and applying them directly into ground motion models. Instead, they illustrate the feasibility of deriving spectral acceleration amplification factors directly from sets of observed records, which are calibrated to parameters that can be mapped uniformly on a regional scale. The result is a geologically calibrated amplification model that can be incorporated into national and regional seismic hazard and risk assessment, ensuring that the corresponding total aleatory variability reflects the predictive capability of the mapped site proxy.
High-resolution surface velocities and strain for Anatolia from Sentinel-1 InSAR and GNSS data
(2020)
Measurements of present-day surface deformation are essential for the assessment of long-term seismic hazard. The European Space Agency's Sentinel-1 satellites enable global, high-resolution observation of crustal motion from Interferometric Synthetic Aperture Radar (InSAR). We have developed automated InSAR processing systems that exploit the first similar to 5 years of Sentinel-1 data to measure surface motions for the similar to 800,000-km(2) Anatolian region. Our new 3-D velocity and strain rate fields illuminate deformation patterns dominated by westward motion of Anatolia relative to Eurasia, localized strain accumulation along the North and East Anatolian Faults, and rapid vertical signals associated with anthropogenic activities and to a lesser extent extension across the grabens of western Anatolia. We show that automatically processed Sentinel-1 InSAR data can characterize details of the velocity and strain rate fields with high resolution and accuracy over large regions. These results are important for assessing the relationship between strain accumulation and release in earthquakes. <br /> Plain Language Summary Satellite-based measurements of small rates of motion of the Earth's surface made at high spatial resolutions and over large areas are important for many geophysical applications including improving earthquake hazard models. We take advantage of recent advances in geodetic techniques in order to measure surface velocities and tectonic strain accumulation across the Anatolia region, including the highly seismogenic and often deadly North Anatolian Fault. We show that by combining Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) data with Global Navigation Satellite System (GNSS) measurements we can enhance our view of surface deformation associated with active tectonics, the earthquake cycle, and anthropogenic processes.
Geochemical processes change the microstructure of rocks and thereby affect their physical behaviour at the macro scale. A micro-computer tomography (micro-CT) scan of a typical reservoir sandstone is used to numerically examine the impact of three spatial alteration patterns on pore morphology, permeability and elastic moduli by correlating precipitation with the local flow velocity magnitude. The results demonstrate that the location of mineral growth strongly affects the permeability decrease with variations by up to four orders in magnitude. Precipitation in regions of high flow velocities is characterised by a predominant clogging of pore throats and a drastic permeability reduction, which can be roughly described by the power law relation with an exponent of 20. A continuous alteration of the pore structure by uniform mineral growth reduces the permeability comparable to the power law with an exponent of four or the Kozeny-Carman relation. Preferential precipitation in regions of low flow velocities predominantly affects smaller throats and pores with a minor impact on the flow regime, where the permeability decrease is considerably below that calculated by the power law with an exponent of two. Despite their complete distinctive impact on hydraulics, the spatial precipitation patterns only slightly affect the increase in elastic rock properties with differences by up to 6.3% between the investigated scenarios. Hence, an adequate characterisation of the spatial precipitation pattern is crucial to quantify changes in hydraulic rock properties, whereas the present study shows that its impact on elastic rock parameters is limited. The calculated relations between porosity and permeability, as well as elastic moduli can be applied for upscaling micro-scale findings to reservoir-scale models to improve their predictive capabilities, what is of paramount importance for a sustainable utilisation of the geological subsurface.
Relative pollen productivity (RPP) estimates are fractionate values, often in relation to Poaceae, that allow vegetation cover to be estimated from pollen counts with the help of models. RPP estimates are especially used in the scientific community in Europe and China, with a few studies in North America. Here we present a comprehensive compilation of available northern hemispheric RPP studies and their results arising from 51 publications with 60 sites and 131 taxa. This compilation allows scientists to identify data gaps in need of further RPP analyses but can also aid them in finding an RPP set for their study region. We also present a taxonomically harmonised, unified RPP dataset for the Northern Hemisphere and subsets for North America (including Greenland), Europe (including arctic Russia), and China, which we generated from the available studies. The unified dataset gives the mean RPP for 55 harmonised taxa as well as fall speeds, which are necessary to reconstruct vegetation cover from pollen counts and RPP values. Data are openly available at https://doi.org/10.1594/PANGAEA.922661 (Wieczorek and Herzschuh, 2020).
Different upper tail indicators exist to characterize heavy tail phenomena, but no comparative study has been carried out so far. We evaluate the shape parameter (GEV), obesity index, Gini index and upper tail ratio (UTR) against a novel benchmark of tail heaviness - the surprise factor. Sensitivity analyses to sample size and changes in scale-to-location ratio are carried out in bootstrap experiments. The UTR replicates the surprise factor best but is most uncertain and only comparable between records of similar length. For samples with symmetric Lorenz curves, shape parameter, obesity and Gini indices provide consistent indications. For asymmetric Lorenz curves, however, the first two tend to overestimate, whereas Gini index tends to underestimate tail heaviness. We suggest the use of a combination of shape parameter, obesity and Gini index to characterize tail heaviness. These indicators should be supported with calculation of the Lorenz asymmetry coefficients and interpreted with caution.
In recent years, nature-based solutions are receiving increasing attention in the field of disaster risk reduction and climate change adaptation as inclusive, no regret approaches. Ecosystem-based adaptation (EbA) can mitigate the impacts of climate change, build resilience and tackle environmental degradation thereby supporting the targets set by the 2030 Agenda, the Paris Agreement and the Sendai Framework. Despite these benefits, EbA is still rarely implemented in practice. To better understand the barriers to implementation, this research examines policy-makers' perceptions of EbA, using an extended version of Protection Motivation Theory as an analytical framework. Through semi-structured interviews with policy-makers at regional and provincial level in Central Vietnam, it was found that EbA is generally considered a promising response option, mainly due to its multiple ecosystem-service benefits. The demand for EbA measures was largely driven by the perceived consequences of natural hazards and climate change. Insufficient perceived response efficacy and time-lags in effectiveness for disaster risk reduction were identified as key impediments for implementation. Pilot projects and capacity building on EbA are important means to overcome these perceptual barriers. This paper contributes to bridging the knowledge-gap on political decision-making regarding EbA and can, thereby, promote its mainstreaming into policy plans.