ALBERT

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: All datasets provided in the operational dataset (Heubeck et al., 2024) of the ICDP project BASE (ICDP 5069) consist of metadata, data and/or images. Here, a summary of explanations of the tables, data and images exported from the database of the project (mDIS BASE) are given and are complimented by additional information on data from measurements done in the laboratory prior to the sampling party. Finally, the sampling data from the first two sam-pling parties are added. Some basic definitions of identifiers used in ICDP, depths corrections and measurements are also introduced.

Description: Large igneous provinces (LIP) are vast (0.2 to 〉1 Mkm3) outpourings of basaltic lava and voluminous intrusions of magmas that have had important environmental consequences, in many cases leading to immense greenhouse gas release and mass extinctions. Magmatic oxygen fugacity (fO2) influences the chemistry of volcanic gases and is an important parameter for examining the links between LIP eruptions and environmental change. To constrain the fO2 of LIP magmas, we report olivine elemental chemistry of 399 crystals from a set of fifteen olivine-rich LIP samples, spanning in age from the Proterozoic (∼1270 Ma) to the Miocene (∼17 Ma). Concentrations of V in olivine are used to show that mafic LIP lavas erupted at +1.20 ± 0.95 ΔFMQ, on average more oxidized than mid ocean ridge basalts (MORB) at −0.28 ± 0.28 ΔFMQ. Mafic LIP magmas show a much larger range than MORB, however. Additionally, fO2 shows a negative correlation with parental magma MgO content, with high MgO lavas approaching the MORB range. This correlation is likely due to sampling of a heterogeneous mixture of oxidized and reduced lithologies, as also sampled by ocean island basalts (OIB). Correlation between fO2 and isotopic ratios such as 143Nd/144Nd demonstrates that the oxidized endmember is geochemically enriched, and may result from subduction recycling of oxidized surficial materials. The high fO2 of primitive LIP magmas demonstrate that they largely emitted oxidized gases during eruption, and furthermore, that LIP magmas associated with mass extinctions have similar magmatic fO2 to those that are not. Global plate tectonic position, magnitude and duration of LIP volcanic eruptions and magmatic degassing, as well as interaction with sedimentary basins in the crust - but not mantle source fO2 - are likely to be the critical factors for whether a LIP was associated with a mass extinction.

Description: Analysis and identifying the displacement characteristics play a key role in timely monitoring and detecting the physical responses of the bridge to ensure the safety of the human and structure. Many previous kinds of research used GNSS data to identify displacement and oscillation modelling of the bridge with different algorithms. This study uses GNSS time-series data to determine linear displacement and model oscillation of the bridge using a procedure including filtering outliers, linear regression, and sin function to identify amplitude in three directions, the plane displacement velocity, spatial displacement velocity, and vibration model of the bridge. The data in the research in the GNSS time-series data from three P5 GNSS receivers of the CHC brand on the Dachongyong bridge in Nanning, China with 1646 observations, at one-hour sample intervals in 68 consecutive days. The plane and spatial velocity of the three points DCQ01, DCQ02, and DCQ03 is 0.0181 mm/h, 0.0185 mm/h; 0.0114 mm/h, 0.0173 mm/h; and 0.0071 mm/h, 0.0082 mm/h respectively. The study results are significant in analyzing and identifying the bridge's displacement characteristics.

Description: Double seismic zones (DSZs) are a feature of some subducting slabs, where intermediate-depth earthquakes (~70–300 km) align along two separate planes. The upper seismic plane is generally attributed to dehydration embrittlement, whereas mechanisms forming the lower seismic plane are still debated. Thermal conductivity of slab minerals is expected to control the temperature evolution of subducting slabs, and therefore their seismicity. However, effects of the potential anisotropic thermal conductivity of layered serpentine minerals with crystal preferred orientation on slab’s thermal evolution remain poorly understood. Here we measure the lattice thermal conductivity of antigorite, a hydrous serpentine mineral, along its crystallographic b- and c-axis at relevant high pressure-temperature conditions of subduction. We find that antigorite’s thermal conductivity along the c-axis is ~3–4 folds smaller than the b-axis.Our numericalmodels further reveal thatwhen the lowthermal-conductivity c-axis is aligned normal to the slab dip, antigorite’s strongly anisotropic thermal conductivity enables heating at the top portion of the slab, facilitating dehydration embrittlement that causes the seismicity in the upper plane of DSZs. Potentially, the antigorite’s thermal insulating effect also hinders the dissipation of frictional heat inside shear zones, promoting thermal runaway along serpentinized faults that could trigger intermediatedepth earthquakes.

Description: Tourmaline is common in rare element pegmatites of the Nb-Y-F (NYF) type in the south-central part of the Proterozoic Sveconorwegian orogen in southern Norway. In the global context, however, tourmaline appears rare in this type of pegmatite. This study aims to explain the unusual tourmaline abundance in these pegmatites and the origin of boron (B) in the respective melts, and to raise awareness of tourmaline in NYF pegmatites generally. Tourmalines from six pegmatites in three Sveconorwegian lithotectonic units: Bamble, Kongsberg and Idefjorden, were investigated in terms of their mineral chemistry and δ11B values, in addition to bulk rock analyses of pegmatites and host rocks. Tourmalines in pegmatites from Bamble and Kongsberg record B isotopic compositions (δ11B = -1.0 to + 9.9 ‰) that are heavy relative to continental crust and mantle sources. In contrast, tourmaline in pegmatites and host rocks from Idefjorden have light B isotopic ratios (δ11B = -14.8 to −12.5 ‰) that are typical crustal values. We suggest that the latter melts were sourced from orthogneisses at depth. We relate the heavy B isotopic composition of Bamble and Kongsberg pegmatites to regional Na-metasomatism by fluids sourced from Mesoproterozoic shallow marine sediments. This is supported by previously published δ11B ratios from metasomatized Bamble host rocks. The spatial association of pegmatites with Na-metasomatism in the basement rocks suggests that metasomatism enhanced the fertility and B-concentration in the affected lithologies, favouring partial melting and the formation of tourmaline-bearing pegmatites. These findings contribute to understanding the petrogenesis of Sveconorwegian pegmatites but they also imply that B can play a greater role in the formation of NYF pegmatites than previously thought and that tourmaline has value as a petrogenetic tool in this type of pegmatites as well as in the Li-Cs-Ta (LCT) type to which is it is more commonly applied.