ALBERT

Description: Rapid assessment of an earthquake’s impact on the affected society is a crucial step in the early phase of disaster management, navigating the need for further emergency response measures. We demonstrate that felt reports collected via the LastQuake service of the European Mediterranean Seismological Center can be utilized to rapidly estimate the probability of a felt earthquake being high impact rather than low impact on a global scale. Our data-driven, transparent, and reproducible method utilizing Bayes’ theorem and kernel density estimation provides results within 10 min for 393 felt events in 2021. Although a separation of high- and low-impact events remains challenging, the cor- rect and unambiguous assessment of a large portion of low-impact events is a key strength of our approach. We consider our method as an inexpensive addition to the pool of earthquake impact assessment tools, one that is fully independent of seismic data and can be utilized in many populated areas on the planet. Although practical deployment of our method remains an open task, we demonstrate the potential to improve disaster management in regions that currently lack expensive seismic instrumentation.

Description: Accelerograms are the primary source for characterizing strong ground motion. It is therefore of paramount interest to have high‐quality recordings free from any nonphysical contamination. Frequently, accelerograms are affected by baseline jumps and drifts, either related to the instrument and/or a major earthquake. In this work, I propose a correction method for these undesired baseline drifts based on segmented linear least squares. The algorithm operates on the integrated waveforms and combines all three instrument components to estimate a model that modifies the baseline to be at zero continuously. The procedure consists of two steps: first a suite of models with variable numbers of discontinuities is derived for all three instrument components. During this process, the number of discontinuities is reduced in a parsimonious way, for example, two very close discontinuities are merged into a single one. In the second step, the optimal model is selected on the basis of the Bayesian information criterion. I exemplify the application on synthetic waveforms with known discontinuities and on observed waveforms from a unified strong‐motion database of the Japan Meteorological Agency (JMA) and the National Research Institute for Earth Science and Disaster Prevention (NIED, Japan) networks for the major events of the 2016 Kumamoto earthquakes. After the baseline jump correction, the waveforms are furthermore corrected for displacement according to Wang et al. (2011). The resulting displacements are comparable to the Interferometric Synthetic Aperture Radar‐derived displacement estimates for the Kumamoto earthquake sequence.

Description: Ground motion with strong‐velocity pulses can cause significant damage to buildings and structures at certain periods; hence, knowing the period and velocity amplitude of such pulses is critical for earthquake structural engineering. However, the physical factors relating the scaling of pulse periods with magnitude are poorly understood. In this study, we investigate moderate but damaging earthquakes (⁠Mw 6–7) and characterize ground‐motion pulses using the method of Shahi and Baker (2014) while considering the potential static‐offset effects. We confirm that the within‐event variability of the pulses is large. The identified pulses in this study are mostly from strike‐slip‐like earthquakes. We further perform simulations using the frequency–wavenumber algorithm to investigate the causes of the variability of the pulse periods within and between events for moderate strike‐slip earthquakes. We test the effect of fault dips, and the impact of the asperity locations and sizes. The simulations reveal that the asperity properties have a high impact on the pulse periods and amplitudes at nearby stations. Our results emphasize the importance of asperity characteristics, in addition to earthquake magnitudes for the occurrence and properties of pulses produced by the forward directivity effect. We finally quantify and discuss within‐ and between‐event variabilities of pulse properties at short distances.

Description: The steady increase of ground-motion data not only allows new possibilities but also comes with new challenges in the development of ground-motion models (GMMs). Data classification techniques (e.g., cluster analysis) do not only produce deterministic classifications but also probabilistic classifications (e.g., probabilities for each datum to belong to a given class or cluster). One challenge is the integration of such continuous classification in regressions for GMM development such as the widely used mixed-effects model. We address this issue by introducing an extension of the mixed-effects model to incorporate data weighting. The parameter estimation of the mixed-effects model, that is, fixed-effects coefficients of the GMMs and the random-effects variances, are based on the weighted likelihood function, which also provides analytic uncertainty estimates. The data weighting permits for earthquake classification beyond the classical, expert-driven, binary classification based, for example, on event depth, distance to trench, style of faulting, and fault dip angle. We apply Angular Classification with Expectation–maximization, an algorithm to identify clusters of nodal planes from focal mechanisms to differentiate between, for example, interface- and intraslab-type events. Classification is continuous, that is, no event belongs completely to one class, which is taken into account in the ground-motionmodeling. The theoretical framework described in this article allows for a fully automatic calibration of ground-motionmodels using large databases with automated classification and processing of earthquake and ground-motion data. As an example, we developed a GMM on the basis of the GMM by Montalva et al. (2017) with data from the strong-motion flat file of Bastías and Montalva (2016) with ∼2400 records from 319 events in the Chilean subduction zone. Our GMMwith the data-driven classification is comparable to the expert-classification-based model. Furthermore, the model shows temporal variations of the between-event residuals before and after large earthquakes in the region.

Description: Surface heat flow is a geophysical variable that is affected by a complex combination of various heat generation and transport processes. The processes act on different lengths scales, from tens of meters to hundreds of kilometers. In general, it is not possible to resolve all processes due to a lack of data or modeling resources, and hence the heat flow data within a region is subject to residual fluctuations. We introduce the REgional HEAT-Flow Uncertainty and aNomaly Quantification (REHEATFUNQ) model, version 2.0.1. At its core, REHEATFUNQ uses a stochastic model for heat flow within a region, considering the aggregate heat flow to be generated by a gamma-distributed random variable. Based on this assumption, REHEATFUNQ uses Bayesian inference to (i) quantify the regional aggregate heat flow distribution (RAHFD) and (ii) estimate the strength of a given heat flow anomaly, for instance as generated by a tectonically active fault. The inference uses a prior distribution conjugate to the gamma distribution for the RAHFDs, and we compute parameters for a uninformed prior distribution from the global heat flow database by Lucazeau (2019). Through the Bayesian inference, our model is the first of its kind to consistently account for the variability in regional heat flow in the inference of spatial signals in heat flow data. Interpretation of these spatial signals and in particular their interpretation in terms of fault characteristics (particularly fault strength) form a long-standing debate within the geophysical community. We describe the components of REHEATFUNQ and perform a series of goodness-of-fit tests and synthetic resilience analyses of the model. While our analysis reveals to some degree a misfit of our idealized empirical model with real-world heat flow, it simultaneously confirms the robustness of REHEATFUNQ to these model simplifications. We conclude with an application of REHEATFUNQ to the San Andreas fault in California. Our analysis finds heat flow data in the Mojave section to be sufficient for an analysis and concludes that stochastic variability can allow for a surprisingly large fault-generated heat flow anomaly to be compatible with the data. This indicates that heat flow alone may not be a suitable quantity to address fault strength of the San Andreas fault.

Description: During the expeditions ARK-VII/1, ARK-VII/3 and ARK-Xl2 sediment cores were taken by "RV Polarstern" from the shelf and the fjords of East Greenland and the Greenland Sea. The magnetic susceptibility and heavy mineral were determined at 48 surface sediment samples from undisturbed box cores. The main objective of this study was the identification of source areas and transport processes of terrigenous sediments at the East Greenland continental margin. The results can be summarized as lollows: 1a) Magnetic susceptibility in the North Atlantic is useful to detect delivery regions of the material transported by currents. b) The magnetic susceptibility is controlled by the ferromagnetic particles of the silt fraction. c) There are four important source areas: . The ferromagnetic particles of the box core PS2644-2 are transported from the Iceland Archipelago. . The material from the Geiki-Plateau effects the magnetic susceptibility in the Scoresby Sund Basin. . The magnetic susceptibility in the shelf regions in the North are produced by material from the fjords. . The ferromagnetic particles in the Greenland Sea are derived from the Mid Atlantic Ridges in the east. d) It is possible to determine the rock type, which delivers the ferromagnetic material because of differences in magnetic susceptibility of different intensity. . The erosion of the basalts of the Geiki-Plateau and the basalts of the Mid Atlantic ridges produce the high magnetic susceptibility in the south. . The magnetic susceptibility on the shelf in the north are probably produced by erosionproducts of the gneises of East Greenland. (2a) Heavy mineral assemblages show a significant difference between material transported by the Transpolar Drift from the Eurasian shelf regions (amphiboles, clinopyroxene, orthopyroxene) and material derived from East Greenland (garnets and opaque minerals). Transport via ice is dominant. b) lt is also possible to show different petrographic provenances (volcanic and metamorphic provenances). These associations verify the source areas. c) The information of heavy mineral composition gives no more detailed hint on the rock type or rock formation in the source area, due to mixing processes, large area of investigation and the sample quantity.

Description: Records of glaciomarine deposition recovered from the West Antarctic continental margin in the Amundsen Sea allow the reconstruction of the behaviour of the West Antarctic Ice Sheet (WAIS) in response to the natural climatic changes of the last 1.8 million years. Contents of gravel-sized and lithogenic components represent the input and redeposition of glaciogenic debris, whereas variations in the proportions of the calcareous sediment fraction reflect palaeoproductivity changes. All proxies, which are regarded as sensitive to a WAIS collapse, changed markedly during the global climatic cycles, but do not confirm a complete disintegration of the WAIS during the Pleistocene.

Description: On- and off-mound sediment cores from Propeller Mound (Hovland Mound province, Porcupine Seabight) were analysed to understand better the evolution of a carbonate mound. The evaluation of benthic foraminiferal assemblages from the off-mound position helps to determine the changes of the environmental controls on Propeller Mound in glacial and interglacial times. Two different assemblages describe the Holocene and Marine Isotope Stage (MIS) 2 and late MIS 3 (~31 kyr BP). The different assemblages are related to changes in oceanographic conditions, surface productivity and the waxing and waning of the British Irish Ice Sheet (BIIS) during the last glacial stages. The interglacial assemblage is related to a higher supply of organic material and stronger current intensities in water depth of recent coral growth. During the last glaciation the benthic faunas showed high abundances of cassidulinid species, implying cold bottom waters and a reduced availability of organic matter. High sedimentation rates and the domination of Elphidium excavatum point to shelf erosion related to sea-level lowering (~50 m) and the progradation of the BIIS onto the shelf. A different assemblage described for the on-mound core is dominated by Discanomalina coronata, Gavelinopsis translucens, Planulina ariminensis, Cibicides lobatulus and to a lower degree by Hyrrokkin sarcophaga. These species are only found or show significantly higher relative abundances in on-mound samples and their maximum contribution in the lower part of the record indicates a higher coral growth density on Propeller Mound in an earlier period. They are less abundant during the Holocene, however. This dataset portrays the boundary conditions of the habitable range for the cold-water coral Lophelia pertusa, which dominates the deep-water reefal ecosystem on the upper flanks of Propeller Mound. The growth of this ecosystem occurs during interglacial and interstadial periods, whereas a retreat of corals is documented in the absence of glacial sediments on-mound. Glacial conditions with cold intermediate waters, a weak current regime and high sedimentation rates provide an unfavourable environmental setting for Lophelia corals to grow. A Late Pleistocene decrease is observed in the mound growth for Propeller Mound, which might face its complete burial in the future, as it already happened to the buried mounds of the Magellan Mound province further north.

Description: The vertical distribution of living (Rose Bengal stained) benthic foraminifers was determined in the upper 15 cm of sediment cores taken along transects extending from the continental shelf of Spitsbergen through the Eurasian Basin of the Arctic Ocean. Cores taken by a multiple corer were raised from 50 stations with water depths between 94 and 4427 m, from areas with moderate primary production values to areas that are among the least productive ones in the world. We believe, that in the Arctic Ocean the vertical distribution of living foraminifers is determined by the restricted availability of food. Live foraminiferal faunas are dominated by potentially infaunal species or epifaunal species. Species confined to the infaunal microhabitat are absent in Arctic sediments that we examined, and predominantly infaunal living species are nowhere dominant. In general, an infaunal mode of life is restricted to the seasonally ice-free areas and thus to areas with at least moderate primary production during the summer period. Under the permanent ice cover living species are usually restricted to the top centimeter of the sediment surface, even though some are able to dwell deeper in the sediment under ice-free conditions.

Description: During the ANT V14 (1986187) and ANT V113 (1987188) cruises of R.V. Polarstern sedirnents from the eastern, southern and central Weddell Sea were sarnpled with a boxcorer andlor a multicorer. The 24 sampling locations are distributed over the whole depth range, from shelf to pelagic environments. Porewater concentrations of aluminium, fluoride, manganese, nitrate, nitrite, oxygen and silicate, the pH and the alkalinity were measured. Of the sediment the opal, calcium carbonate and organic carbon content were quantified. The 210Pb-profile was measured for three sedirnent cores. This investigation deals with the estimation of the amounts of opal and organic carbon (Corg) that are transported into the sediment, the regional distribution of these flux rates and the early diagenetic processes that control the preservation of organic carbon and opal in the sediment. The flux and degradation rates of organic carbon were determined by modelling the rneasured oxygen and nitrate profiles. The highest flux and degradation rates were found in the eastern shelf sediments. Due to the high Corg-flux (〉500 mmol C m**-2 a-1) in this area the oxic environment is restricted to the upper 3 cm of the sediment. In contrast to this, the oxic Zone in the pelagic sedirnents of the Weddell Sea has probably an extension of a few meters. The Corg-flux here, computed from the flux of nitrate throug h the sedimentlwater-interface, is less than 50 mmol C m**-2 a**-1. The flux of organic carbon into the sediments of the continental slope area is usually intermediate between the values computed for the shelf and pelagic sediments. Exceptions are the continental slope region north of Halley Bay. In these sediments the measured oxygen and nitrate profiles indicate a relatively high organic carbon flux. This could be a result of the recurrent development of a coastal polynia in this area. The bioturbation rate determined in this region by a 210Pb-profile is 0,019 cm**2 a**-1. In the Weddell Sea the opal content at the sediment surface (0-1 cm depth) varies between 0,1 and 7 %-wt. These opal concentrations are rnuch lower than the opal contents determined for the sediments of the ROSS Sea by Ledford-Hoffmann et al. (1986 doi:10.1016/0016-7037(86)90263-2). Therefore the importance of the Antarctic shelf regions for the global silica cycle as stated by Ledford-Hoffmann et al. (1986) has to be reconsidered. The regional distribution of the opal content and the computed opal flux rates are correlated with the organic carbon flux rates. The processes controlling the preservation of opal are discussed based On the measured aluminium and silicate concentrations in the Pore water and the opal content of the sediment.The depth distribution of the Si- and Al-concentration of the porewater indicates that the reconstitution of clay minerals takes place in the immediate vicinity of the sediment-water nterface. A characterization of these minerals e.g. the estimation of the Si/AI-ratio (Mackin and Aller, 1984 a doi:10.1016/0016-7037(84)90251-5, 1984 b doi:10.1016/0016-7037(84)90252-7) is not possible. With the program WATEQ2 saturation indices are computed to estimate which minerals could reconstitute. In this context the applicability of programs like WATEQ2 for computations of the species distribution and saturation indices in solutions with the ionic strength of sea water is investigated.