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1. Ground‐Motion Amplification in Cook Inlet Region, Alaska, from Intermediate‐Depth Earthquakes, Including the 2018 Mw 7.1 Anchorage Earthquake

   https://doi.org/10.1785/0220190179  

   Moschetti, Morgan P.; Thompson, Eric M.; Rekoske, John; Hearne, Michael G.; Powers, Peter M.; McNamara, Daniel E.; Tape, Carl (November 2019, Seismological Research Letters)

   null (Ed.)

   Abstract We measure pseudospectral and peak ground motions from 44 intermediate‐depth Mw≥4.9 earthquakes in the Cook Inlet region of southern Alaska, including those from the 2018 Mw 7.1 earthquake near Anchorage, to identify regional amplification features (0.1–5  s period). Ground‐motion residuals are computed with respect to an empirical ground‐motion model for intraslab subduction earthquakes, and we compute bias, between‐, and within‐event terms through a linear mixed‐effects regression. Between‐event residuals are analyzed to assess the relative source characteristics of the Cook Inlet earthquakes and suggest a difference in the scaling of the source with depth, relative to global observations. The within‐event residuals are analyzed to investigate regional amplification, and various spatial patterns manifest, including correlations of amplification with depth of the Cook Inlet basin and varying amplifications east and west of the center of the basin. Three earthquake clusters are analyzed separately and indicate spatial amplification patterns that depend on source location and exhibit variations in the depth scaling of long‐period basin amplification. The observations inform future seismic hazard modeling efforts in the Cook Inlet region. More broadly, they suggest a greater complexity of basin and regional amplification than is currently used in seismic hazard analyses. 

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2. The 2023 US 50-State National Seismic Hazard Model: Overview and implications

   https://doi.org/10.1177/87552930231215428  

   Petersen, Mark D; Shumway, Allison M; Powers, Peter M; Field, Edward H; Moschetti, Morgan P; Jaiswal, Kishor S; Milner, Kevin R; Rezaeian, Sanaz; Frankel, Arthur D; Llenos, Andrea L; et al (February 2024, Earthquake Spectra)

   The US National Seismic Hazard Model (NSHM) was updated in 2023 for all 50 states using new science on seismicity, fault ruptures, ground motions, and probabilistic techniques to produce a standard of practice for public policy and other engineering applications (defined for return periods greater than ∼475 or less than ∼10,000 years). Changes in 2023 time-independent seismic hazard (both increases and decreases compared to previous NSHMs) are substantial because the new model considers more data and updated earthquake rupture forecasts and ground-motion components. In developing the 2023 model, we tried to apply best available or applicable science based on advice of co-authors, more than 50 reviewers, and hundreds of hazard scientists and end-users, who attended public workshops and provided technical inputs. The hazard assessment incorporates new catalogs, declustering algorithms, gridded seismicity models, magnitude-scaling equations, fault-based structural and deformation models, multi-fault earthquake rupture forecast models, semi-empirical and simulation-based ground-motion models, and site amplification models conditioned on shear-wave velocities of the upper 30 m of soil and deeper sedimentary basin structures. Seismic hazard calculations yield hazard curves at hundreds of thousands of sites, ground-motion maps, uniform-hazard response spectra, and disaggregations developed for pseudo-spectral accelerations at 21 oscillator periods and two peak parameters, Modified Mercalli Intensity, and 8 site classes required by building codes and other public policy applications. Tests show the new model is consistent with past ShakeMap intensity observations. Sensitivity and uncertainty assessments ensure resulting ground motions are compatible with known hazard information and highlight the range and causes of variability in ground motions. We produce several impact products including building seismic design criteria, intensity maps, planning scenarios, and engineering risk assessments showing the potential physical and social impacts. These applications provide a basis for assessing, planning, and mitigating the effects of future earthquakes. 

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3. A Discontinuous Galerkin Method for Simulating 3D Seismic Wave Propagation in Nonlinear Rock Models: Verification and Application to the M _w 7.8 2015 Gorkha, Nepal Earthquake

   https://doi.org/10.1029/2025JB031378  

   Niu, Zihua; Gabriel, Alice‐Agnes; Wolf, Sebastian; Ulrich, Thomas; Lyakhovsky, Vladimir; Igel, Heiner (July 2025, Journal of Geophysical Research: Solid Earth)

   Abstract The nonlinear mechanical responses of rocks and soils to seismic waves play an important role in earthquake physics, influencing ground motion from source to site. Continuous geophysical monitoring, such as ambient noise interferometry, has revealed co‐seismic wave speed reductions extending tens of kilometers from earthquake sources. However, the mechanisms governing these changes remain challenging to model, especially at regional scales. Using a nonlinear damage model constrained by laboratory experiments, we develop and apply an open‐source 3D discontinuous Galerkin method to simulate regional co‐seismic wave speed changes during the 2015 M_w7.8 Gorkha earthquake. We find pronounced spatial variations of co‐seismic wave speed reduction, ranging from <0.01% to >50%, particularly close to the source and within the Kathmandu Basin, while disagreement with observations remains. The most significant reduction occurs within the sedimentary basin and varies with basin depths, whereas wave speed reductions correlate with the fault slip distribution near the source. By comparing ground motions from simulations with elastic, viscoelastic, elastoplastic, and nonlinear damage rheologies, we demonstrate that the nonlinear damage model effectively captures low‐frequency ground motion amplification due to strain‐dependent wave speed reductions in soft sediments. We verify the accuracy of our approach through comparisons with analytical solutions and assess its scalability on high‐performance computing systems. The model shows near‐linear strong and weak scaling up to 2,048 nodes, enabling efficient large‐scale simulations. Our findings provide a physics‐based framework to quantify nonlinear earthquake effects and emphasize the importance of damage‐induced wave speed variations for seismic hazard assessment and ground motion predictions. 

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4. Topographic Response to Simulated Mw 6.5–7.0 Earthquakes on the Seattle Fault

   https://doi.org/10.1785/0120210269  

   Stone, Ian; Wirth, Erin A.; Frankel, Arthur D. (May 2022, Bulletin of the Seismological Society of America)

   ABSTRACT We explore the response of ground motions to topography during large crustal fault earthquakes by simulating several magnitude 6.5–7.0 rupture scenarios on the Seattle fault, Washington State. Kinematic simulations are run using a 3D spectral element code and a detailed seismic velocity model for the Puget Sound region. This model includes realistic surface topography and a near-surface low-velocity layer; a mesh spacing of ∼30 m at the surface allows modeling of ground motions up to 3 Hz. We simulate 20 earthquake scenarios using different slip distributions and hypocenter locations on a planar fault surface. Results indicate that average ground motions in simulations with and without topography are similar. However, shaking amplification is common at topographic highs, and more than a quarter of all sites experience short-period (≤2 s) ground-motion amplification greater than 25%–35%, compared with models without topography. Comparisons of peak ground velocity at the top and bottom of topographic features demonstrate that amplification is sensitive to period, with the greatest amplifications typically manifesting near a topographic feature’s estimated resonance frequency and along azimuths perpendicular to its primary axis of elongation. However, interevent variability in topographic response can be significant, particularly at shorter periods (<1 s). We do not observe a clear relationship between source centroid-to-site azimuths and the strength of topographic amplification. Overall, our results suggest that although topographic resonance does influence the average ground motions, other processes (e.g., localized focusing and scattering) also play a significant role in determining topographic response. However, the amount of consistent, significant amplification due to topography suggests that topographic effects should likely be considered in some capacity during seismic hazard studies. 

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5. Compilation and Forecasting of Paleoliquefaction Evidence for the Strength of Ground Motions in the U.S. Pacific Northwest: A Digital Dataset (Version 2)

   https://doi.org/10.17603/ds2-fqkr-h615  

   Rasanen, Ryan; Marafi, Nasser; Maurer, Brett (January 2021, Designsafe-CI)

   In the U.S. Pacific Northwest (PNW), the historic earthquake record is often insufficient to provide inputs to seismic-hazard analyses or to inform ground-motion predictions for certain seismic sources (e.g., the Cascadia Subduction Zone, CSZ). As a result, paleoseismic studies are commonly used to infer information about the seismic hazard. However, among the many forms of coseismic evidence, soil liquefaction provides the best, if not only, evidence from which the intensities of previous ground motions may be constrained. Accordingly, the overarching goal of this research is to use paleoliquefaction to elucidate previous ground motions in the PNW – both for CSZ events and others – and to further constrain the locations, magnitudes, and recurrence rates of such ruptures. Towards that goal, this paper: (i) reviews current paleoliquefaction inverse-analysis methods and their limited, prior applications in the PNW; (ii) compiles all PNW paleoliquefaction evidence from the literature into a GIS database, resulting in data from 185 study sites (e.g., feature locations, types, sizes, and ages); and (iii) develops maps – specific to the CSZ – that forecast paleoliquefaction for 30 different simulations of a CSZ event. These maps can be used to guide field explorations for new evidence, such that they are conducted efficiently and strategically, considering the apparent utility of evidence toward constraint of CSZ ground-motion models. Of additional utility, this process provides regional ground-motion predictions for physics-based simulations of an M9 event, to include expected site effects. Collectively, the maps of expected shaking intensity and liquefaction may be useful in downstream hazard modelling, regional loss estimation, policy development, and science communication. Ultimately, as more paleoliquefaction evidence is identified and studied, better constraint of regional ground-motion hazards will result. Version 2 (this posting) supersedes Version 1 (10.17603/ds2-jm19-2w09). Updates include GIS rasters that provide regional ground-motion intensity predictions (PGA, PGV) for 30 physics-based simulations of an M9 event, to include expected site effects 

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