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Computational simulations have become central to the seismic analysis and design of major infrastructure over the past several decades. Most major structures are now “proof tested” virtually through representative simulations of earthquake-induced response. More recently, with the advancement of high-performance computing (HPC) platforms and the associated massively parallel computational ecosystems, simulation is beginning to play a role in increased understanding and prediction of ground motions for earthquake hazard assessments. However, the computational requirements for regional-scale geophysics-based ground motion simulations are extreme, which has restricted the frequency resolution of direct simulations and limited the ability to perform the large number of simulations required to numerically explore the problem parametric space. In this article, recent developments toward an integrated, multidisciplinary earth science-engineering computational framework for the regional-scale simulation of both ground motions and resulting structural response are described with a particular emphasis on advancing simulations to frequencies relevant to engineered systems. This multidisciplinary computational development is being carried out as part of the US Department of Energy (DOE) Exascale Computing Project with the goal of achieving a computational framework poised to exploit emerging DOE exaflop computer platforms scheduled for the 2022–2023 timeframe.

The existing observational database of the regional-scale distribution of strong ground motions and measured building response for major earthquakes continues to be quite sparse. As a result, details of the regional variability and spatial distribution of ground motions, and the corresponding distribution of risk to buildings and other infrastructure, are not comprehensively understood. Utilizing high-performance computing platforms, emerging high-resolution, physics-based ground motion simulations can now resolve frequencies of engineering interest and provide detailed synthetic ground motions at high spatial density. This provides an opportunity for new insight into the distribution of infrastructure seismic demands and risk. In the work presented herein, the EQSIM fault-to-structure computational framework described in a companion paper, McCallen et al., is employed to investigate the regional-scale response of buildings to large earthquakes. A representative M = 7.0 strike-slip event is used to explore the distribution and amplitude of building demand, and comparisons are made between building response computed with fault-to-structure simulations and building response computed with existing measured near-fault earthquake records. New information on the distribution and variability of building response from high-performance parallel simulations is described and analyzed, and favorable first comparisons between building response predicted with both fault-to-structure simulations and real ground motions records are presented.

We investigated the effects of fault geometry and assumed minimum shear wavespeed (VS min) on 3D ground-motion simulations (0–2.5 Hz) in general, using a moment magnitude (Mw) 6.5 earthquake on the Hayward fault (HF). Simulations of large earthquakes on the northeast-dipping HF using the U.S. Geological Survey (USGS) 3D seismic model have shown intensity asymmetry with stronger shaking for the Great Valley Sequence east of the HF (hanging wall) relative to the Franciscan Complex to the west (footwall). We performed simulations with three fault geometries in both plane-layered (1D) and 3D models. Results show that the nonvertical fault geometries result in larger motions on the hanging wall relative to the vertical fault for the same Earth model with up to 50% amplifications in single-component peak ground velocity (PGV) within 10 km of the rupture. Near-fault motions on the footwall are reduced for the nonvertical faults, but less than they are increased on the hanging wall. Simulations assuming VS min values of 500 and 250 m=s reveal that PGVs are on average 25% higher west of the HF when using the lower VS min, with some locations amplified by a factor of 3. Increasing frequency content from 2.5 to 5 Hz increases PGV values. Spectral ratios of these two VS min cases show average amplifications of 2–4 (0.5–1.5 Hz) for the lower VS min west of the fault. Large differences (up to 2×) in PGV across the HF from previous studies persist even for the case with a vertical fault or VS min of 250 m=s. We conclude that assuming a VS min of 500 m=s underestimates intensities west of the HF for frequencies above 0.5 Hz, and that low upper crustal (depth < 10 km) shear wavespeeds defined in the 3D model contribute most to higher intensities east of the HF.

We report on high-performance computing (HPC) fully deterministic simulation of ground motions for a moment magnitude (Mw) 7.0 scenario earthquake on the Hayward fault resolved to 5 Hz using the SW4 finite-difference code. We computed motions obeying physics-based 3D wave propagation at a regional scale with an Mw 7.0 kinematic rupture model generated following Graves and Pitarka (2016). Both plane-layered (1D) and 3D Earth models were considered, with 3D subsurface material properties and topography interpolated from a model of the U.S. Geological Survey (USGS). The resulting ground-motion intensities cover a broader frequency range than typically considered in regional-scale simulations, including higher frequencies relevant for engineering analysis of structures. Median intensities for sites across the domain are within the reported between-event uncertainties (τ) of ground-motion models (GMMs) across spectral periods 0.2-10 s (frequencies 0.1-5 Hz). The within-event standard deviation ϕ of ground-motion intensity measurement residuals range 0.2-0.5 natural log units with values consistently larger for the 3D model. Source-normalized ratios of intensities (3D/ 1D) reveal patterns of path and site effects that are correlated with known geologic structure. These results demonstrate that earthquake simulations with fully deterministic wave propagation in 3D Earth models on HPC platforms produce broadband ground motions with median and within-event aleatory variability consistent with empirical models. Systematic intensity variations for the 3D model caused by path and site effects suggest that these epistemic effects can be estimated and removed to reduce variation in site-specific hazard estimates. This study motivates future work to evaluate the validity of the USGS 3D model and investigate the development of path and site corrections by running more scenarios.

This study analyzed the Democratic People's Republic of Korea's (DPRK) fourth (DPRK4, 6 January 2016 MW 4.49) and sixth (DPRK6, 7 September 2017 MW 5.2) declared nuclear tests, employing a joint seismic and Interferometric Synthetic Aperture Radar (InSAR) inversion to improve understanding of these events and enhance moment tensor (MT) inversion capabilities. The recent efforts have focused on employing seismic waveform and InSAR geodetic deformation data separately to analyze these and the previous nuclear tests (e.g., Chiang et al., 2018; Myers et al., 2018; Wang et al., 2018). Building upon our previous work (Chi-Durán et al., 2021), we performed a joint regional waveform, first-motion (FM) polarity, and surface displacement inversion, which demonstrated improved source-type discrimination, a revised MT solution with reduced scalar moment uncertainty, and an independently constrained location. In this article, we build on the previous results for DPRK6 by including an analysis using a four-layered velocity model with free-surface topography to compute the near-source static deformation Green's functions. The model consists of a 50 m basalt layer (VP = 2.07km/s, VS = 1.2km/s), a 250 m stratified volcanic deposit layer (VP = 1.73km/s VS = 1km/s), a 700 m weathered granodiorite layer (VP = 2.5km/s, VS = 1.3km/s) and a granodiorite half-space (VP = 5.35km/s, VS = 3.09km/s). The half-space shares the velocity of the regional MDJ2 velocity model (Ford et al., 2010), which has proven effective for waveform inversion in the region. This model considers the range of reported values for various lithologies and weathering effects. Our findings show that using the layered velocity model enhances the recovery of source location and depth for both the explosions by improving fits and reducing uncertainties. The joint inversion also improves source-type discrimination and better constrains the scalar seismic moment necessary for downstream yield estimation. [ABSTRACT FROM AUTHOR]

Seismic ground-motion data provide valuable constraints on explosion characteristics, such as yield and height-of-burst/depth-of-burial (HOB/DOB). This study investigated a range of seismic amplitude features and their efficacy in minimizing errors associated with yield estimation. Using a set of explosion recordings from experiments conducted in alluvium and sedimentary rock geologies, we investigated the effectiveness of three different seismic feature types over a range of different frequencies. Using both velocity and displacement data, we investigated the zero-to-peak (ZTP) amplitude of the first arriving P wave, the peak-to-peak (PTP) amplitude of the first arriving P wave, and the Prms amplitude over various time windows starting with the P wave. These three basic features were measured on both vertical component only data and the vertical–radial vector sum. In total, there were 56 different combinations investigated. Our seismic models combine the effects of scaled range and scaled HOB/DOB on the observed seismic features. The results show that the vertical–radial vector sum of the ZTP amplitudes measured on displacement seismograms most consistently produce models with the smallest difference between predicted amplitude values and observed amplitude values when accounting for both alluvium and sedimentary rock lithology. The improvement in fit to the data when incorporating the difference in source lithology is significant. If an alluvium lithology is assumed for a sedimentary rock lithology, the difference in yield could be up to ∼3.0 times the appropriate yield in the far field.

We performed fully deterministic broadband (0–4 Hz) high-performance computing ground motion simulations of a magnitude 7.0 scenario earthquake on the Hayward Fault (HF) in the San Francisco Bay Area of Northern California. Simulations consider average one-dimensional (1-D) and three-dimensional (3-D) anelastic structure with flat and topographic free surfaces. Ground motion intensity measures (GMIMs) for the 3-D model display dramatic differences across the HF due to geologic heterogeneity, with low wave speeds east of the HF amplifying motions. The median GMIMs agree well with Ground Motion Prediction Equations (GMPEs); however, the 3-D model generates more scatter than the 1-D model. Ratios of 3-D/1-D GMIMs from the same source allow isolation of path and site effects for the 3-D model. These ratios show remarkably similar trends as site-specific factors for the GMPE predictions, suggesting that wave propagation effects in our 3-D simulations are on average consistent with empirical data.

Modernizing SW4 for massively parallel time-domain simulations of earthquake ground motions in 3D earth models increases resolution and provides ground motion estimates for critical infrastructure risk evaluations. Simulations of ground motions from large (M ≥ 7.0) earthquakes require domains on the order of 100 to500 km and spatial granularity on the order of 1 to5 m resulting in hundreds of billions of grid points. Surface-focused structured mesh refinement (SMR) allows for more constant grid point per wavelength scaling in typical Earth models, where wavespeeds increase with depth. In fact, MR allows for simulations to double the frequency content relative to a fixed grid calculation on a given resource. The authors report improvements to the SW4 algorithm developed while porting the code to the Cori Phase 2 (Intel Xeon Phi) systems at the National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory. Investigations of the performance of the innermost loop of the calculations found that reorganizing the order of operations can improve performance for massive problems.

We present a new model of radially anisotropic seismic wavespeeds for the crust and upper mantle of a broad region of the Middle East and Southwest Asia (MESWA) derived from adjoint waveform tomography. The new model enables fully 3D simulations of complete three-component waveforms and provides improved fits that were not possible with previous models. We inverted over 32,000 waveforms from 192 earthquakes recorded by over 1000 openly available broadband seismic stations from permanent and temporary networks in the region with highly uneven coverage. Inversion iterations proceeded from the period band 50-100 s in six stages and 54 total iterations reducing the minimum period to 30 s. Our final model, MESWA, improves waveform fits compared to the starting and other models for both the data used in the inversion and an independent validation set of 66 events. Restitution tests indicate that the model resolves features in the central part of the model to depths of about 150 km. The new model reveals tectonic features imaged by other studies and methods but in a new holistic model of anisotropic shear and compressional wavespeeds (VS and VP, respectively) covering a larger domain with smaller scale length and amplified features. Examples include low crustal VS in the Tethyan belt and low mantle VS following divergent (Gulf of Aden, Red Sea) and transform (Dead Sea fault) margins of the Arabian plate. Low VS is imaged below Cenozoic volcanic centers of the Mecca-Madina-Nafud Line, Arabian Peninsula, and the Türkiye-Iran border region. Elevated VS tracks Makran subduction under southeast Iran with near vertical dip. MESWA could be used as a starting model for further improvements, say, using waveforms from in-country seismic networks that are not currently openly available and/or smaller-scale studies targeting a shorter period. The model could be used to improve earthquake hazard studies and nuclear explosion monitoring. [ABSTRACT FROM AUTHOR]

Seismic tomography is the most abundant source of information about the internal structure of the Earth at scales ranging from a few meters to thousands of kilometers. It constrains the properties of active volcanoes, earthquake fault zones, deep reservoirs and storage sites, glaciers and ice sheets, or the entire globe. It contributes to outstanding societal problems related to natural hazards, resource exploration, underground storage, and many more. The recent advances in seismic tomography are being translated to nondestructive testing, medical ultrasound, and helioseismology. Nearly 50 yr after its first successful applications, this article offers a snapshot of modern seismic tomography. Focused on major challenges and particularly promising research directions, it is intended to guide both Earth science professionals and early-career scientists. The individual contributions by the coauthors provide diverse perspectives on topics that may at first seem disconnected but are closely tied together by a few coherent threads: multiparameter inversion for properties related to dynamic processes, data quality, and geographic coverage, uncertainty quantification that is useful for geologic interpretation, new formulations of tomographic inverse problems that address concrete geologic questions more directly, and the presentation and quantitative comparison of tomographic models. It remains to be seen which of these problems will be considered solved, solved to some extent, or practically unsolvable over the next decade. [ABSTRACT FROM AUTHOR]

The Red Sea Rift, an archetype of a newly formed ocean basin, is an ideal environment in which to study the controversial processes associated with continental rifting. Different models have been proposed to explain how rifting in the Red Sea evolved; however, accurate constraints on lithospheric structure have not been available to discriminate rifting models. We use the S-wave receiver function technique to produce the first images of the lithosphere-asthenosphere boundary (LAB) structure along the Red Sea and throughout the Arabian Peninsula. Lithospheric thickness varies considerably, with thin lithosphere centered on the rift axis, thickening toward the Arabian interior. Gravity data are well fit by our structural model and indicate that high surface topography along the rift flank is not in isostatic equilibrium, requiring dynamic compensation for its support. While our derived structure is consistent with active rifting processes, previous studies demonstrated that the Red Sea initiated as a passive rift. Therefore, our results suggest a two-stage rifting history, where extension and erosion by flow in the underlying asthenosphere are responsible for variations in LAB depth. LAB topography guides asthenospheric flow beneath western Arabia and the Red Sea, demonstrating the important role lithospheric variations play in the thermal modification of tectonic environments. (c) 2007 Elsevier B.V. All rights reserved.

Site-specific variation in relative habitat abundance and disturbance regimes may produce differences in habitat preferences of associated populations. An evaluation of the predictive power of habitat selection models across space would benefit our understanding of the reliability of models of selection and space use in predicting animal occurrence. We used presence-absence data from winter surveys of moose (Alces alces (L., 1758)) to estimate resource selection functions (RSFs) across two study sites using Far North Land Cover updated with recent disturbance from fire and timber harvest. Moose selected foraging habitat (e.g., deciduous land cover) and for increasing deciduous foliage cover (ΔNDVI, i.e., the difference in the normalized difference vegetation index). Snow depth negatively influenced habitat selection, likely due to increased predation risk and reduced movement and foraging efficiency. Models lost little predictive power when applied to another site based on comparison of receiver operating characteristic (ROC) curves. Our results corroborated the current body of knowledge concerning moose habitat selection, i.e., moose preferentially use forest stands dominated by deciduous species, but suggested that moose strongly avoided very recently disturbed areas. Minimal site-specific variation and ROC comparison suggests that RSFs may be extended into novel systems, given adequate consideration for habitat quality and abundance, thereby simplifying management needs of this important species. Key words: Alces alces, disturbance, habitat selection, logistic regression, management, moose, remote sensing, receiver operating characteristic, resource selection function. Les variations propres aux sites des regimes relatifs d'abondance et de perturbation de l'habitat peuvent produire differentes preferences en matiere d'habitat chez les populations associees. Une evaluation de la puissance predictive de modeles de selection d'habitat dans l'espace serait utile pour mieux comprendre la fiabilite des modeles de selection et d'utilisation de l'espace pour ce qui est de predire la presence d'animaux. Nous avons utilise des donnees de presence -absence tirees d'enquetes hivernales sur les orignaux (Alces alces (L., 1758)) pour estimer les fonctions de selection des ressources (FSR) dans deux sites d'etude en utilisant l'ensemble de donnees Couverture du territoire du Grand Nord mis a jour pour y inclure les perturbations recentes dues au feu et a la recolte du bois. Les choix des orignaux etaient axes sur des habitats d'approvisionnement (p. ex. couverture terrestre de feuillus) et une plus grande couverture de feuillage caduque (ΔNDVI, c.-a-d., la variation de l'indice de vegetation par difference normalisee). La profondeur de la neige avait une influence negative sur la selection d'habitat, probablement en raison du risque de predation accru et de la reduction de l'efficacite des deplacements et de l'approvisionnement. Les modeles perdaient peu de leur puissance predictive quand ils etaient appliques a un autre site sur la base de la comparaison de courbes de fonction d'efficacite du recepteur (FER). Nos resultats corroborent les connaissances actuelles sur la selection d'habitat par les orignaux, a savoir qu'ils utilisent preferentiellement des peuplements forestiers oU dominent des essences a feuilles caduques, mais indiqueraient qu'ils evitent fortement les zones recemment perturbees. Des variations propres aux sites tres limitees et la comparaison des FER donnent a penser que les FSR pourraient etre elargies a de nouveaux systemes en tenant adequatement compte de la qualite et de l'abondance des habitats, ce qui simplifierait les besoins de gestion pour cette importante espece. [Traduit par la Redaction] Mots-cles: Alces alces, perturbation, selection de l'habitat, regression logistique, gestion, orignal, teledetection, fonction d'efficacite du recepteur, fonction de selection des ressources., Introduction The foraging ecology of moose (Alces alces (L., 1758)) is well documented, and they spend much of their active time foraging across various habitat types (Belovsky 1981). While aquatic [...]

We used remote video cameras to assess seasonal diet composition of woodland caribou (Rangifer tarandus tarandus (L., 1758)) at three areas across the boreal forest of Ontario. Caribou consume lichens in winter, but we expected they would significantly reduce lichen consumption in favour of higher protein levels in green plants in summer. We sampled videos from 23 caribou, from 2 years, to derive seasonal diet composition. Diet differed among seasons and study areas, except in winter when lichens dominated. Diet breadth doubled from winter to summer, but overlap between seasons was still >60%. Green plants were less commonly eaten than we expected, only three genera were preferred, and few species constituted more than 2% of the diet. Preferred foods varied by land-cover types. Diet differed between managed and unmanaged landscapes but did not result from use of plant species found in successional habitats. Caribou selected a nonoptimal diet in the snow-free seasons, especially with respect to protein, suggesting factors other than nutrition influenced diet choice, and indicating the possibility of bottom-up limitation on production. Key words: woodland caribou, boreal, diet selection, lichens, bottom-up limitation, Rangifer tarandus tarandus. Nous avons utilise des cameras video a distance pour evaluer la composition saisonniere du regime alimentaire du caribou forestier (Rangifer tarandus tarandus (L., 1758)) dans trois regions de la foret boreale ontarienne. Les caribous consomment des lichens en hiver, mais il etait attendu qu'ils reduiraient significativement leur consommation de lichens en ete, pour se tourner vers les plantes vertes, qui offrent de plus fortes teneurs en proteines. Nous avons echantillonne des videos de 23 caribous sur 2 ans, afin de determiner la composition saisonniere du regime alimentaire. Ce dernier variait selon la saison et la region etudiee, sauf en hiver, quand les lichens predominaient. L'etendue du regime alimentaire etait deux fois plus grande en ete qu'en hiver, mais le chevauchement entre les saisons etait neanmoins de >60 %. Les plantes vertes etaient moins largement consommees que prevu, seuls trois genres etaient privilegies, et peu d'especes constituaient plus de 2 % de l'alimentation. Les aliments privilegies variaient selon le type de couverture du sol. Le regime alimentaire variait selon que le paysage faisait ou non l'objet d'une gestion, mais aucune difference ne decoulait de l'utilisation d'especes de plantes presentes dans les habitats de succession. Les caribous choisissaient un regime alimentaire non optimal durant les saisons sans neige, particulierement en ce qui concerne les proteines, donnant a penser que des facteurs autres que la nutrition influencent les choix alimentaires et indiquant la possibilite d'une limitation ascendante de la production. [Traduit par la Redaction] Mots-cles: caribou forestier, boreal, choix du regime alimentaire, lichens, limitation ascendante, Rangifer tarandus tarandus., Introduction Woodland caribou (Rangifer tarandus tarandus (L., 1758)) is a threatened or endangered species depending on the jurisdiction in Canada. Although recovery planning has been instituted to try to conserve [...]