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1. Regional moment tensor estimation with 3D velocity models – Application to the 2017 Hojedk, Iran sequence and performance assessment

   https://doi.org/10.1093/gji/ggag244  

   Rodriguez_Cardozo, Felix; Braunmiller, Jochen; Ghods, Abdolreza; Sawade, Lucas; Örsvuran, Ridvan; Bozdag, Ebru (June 2026, Geophysical Journal International)

   Summary We estimated seismic moment tensors (MTs) for the 2017 magnitude M6 Hojedk, Central Iran, earthquake triplet and their aftershocks, employing 1D and 3D regional and global velocity models to evaluate source parameter stability and resolution fitting in-country waveform data. We used the Moment Tensor Uncertainty Quantification (MTUQ) software, which performs a grid search for MT estimation and uncertainty analysis. For the regional 3D velocity model, we used MEAD-M20, a full-waveform inversion model of the Middle East derived from fitting 15-s body waves with 30-s body and surface waves. We compared the regional 1D- and 3D-based results with an existing database of deviatoric MT solutions, and for both regional velocity models, we found good agreement. However, for periods T ≥ 25–30 s and events with moment magnitudes Mw≥ 4.5, the 3D regional synthetic seismograms outperformed the 1D regional model, reducing waveform misfits, time shifts, and non-double-couple contributions. We consider non-double-couple contributions spurious and their reduction an improvement, as previous studies of the sequence found predominantly shear faulting on reverse faults. Furthermore, uncertainty analysis shows that the moment tensor, non-double-couple component, magnitude, and depth are more tightly constrained for the 3D model. The current 3D model shows no clear improvements relative to the 1D model in terms of misfit, time-shifts, and non-double-couple contributions at short periods T ≈ 15-25 s relevant for modeling smaller events. Using the regional models results in lower misfits and tighter constraints on the MT solutions than with the global 1D PREM and the 3D S2.9EA models. Improved MT estimation and parameter resolution for moderate-to-large events using in-country data validate the recently developed 3D Middle East velocity model. Further model refinements are needed to model shorter-period data required to analyze and improve the resolution of smaller (M ≤ 4) seismic events. Such improvements are within reach by using available in-country data and well-constrained MT solutions from a regional moment tensor database. 

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2. Shallow Fault Zone Structure Affects Rupture Dynamics and Ground Motions of the 2019 Ridgecrest Sequence to Regional Distances

   https://doi.org/10.1029/2025JB031194  

   Schliwa, Nico; Gabriel, Alice‐Agnes; Ben‐Zion, Yehuda (June 2025, Journal of Geophysical Research: Solid Earth)

   Abstract Seismic faults are surrounded by damaged rocks with reduced rigidity and enhanced attenuation. These damaged fault zone structures can amplify seismic waves and affect earthquake dynamics, yet they are typically omitted in physics‐based regional ground motion simulations. We report on the significant effects of a shallow, flower‐shaped fault zone in foreshock‐mainshock 3D dynamic rupture models of the 2019 Ridgecrest earthquake sequence. We find that the fault zone structure both amplifies and reduces ground motions not only locally but at distances exceeding 100 km. This impact on ground motions is frequency‐ and magnitude‐dependent, particularly affecting higher frequency ground motions from the foreshock because its corner frequency is closer to the fault zone's fundamental eigenfrequency. Within the fault zone, the shallow transition to a velocity‐strengthening frictional regime leads to a depth‐dependent peak slip rate increase of up to 70% and confines fault zone‐induced supershear transitions mostly to the fault zone's velocity‐weakening roots. However, the interplay of fault zone waves, free surface reflections, and rupture directivity can generate localized supershear rupture, even in narrow velocity‐strengthening regions, which are typically thought to inhibit supershear rupture. This study demonstrates that shallow fault zone structures may significantly affect intermediate‐ and far‐field ground motions and cause localized supershear rupture penetrating into velocity‐strengthening regions, with important implications for seismic hazard assessment. 

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3. Correcting Biases from Velocity Structures in Moment Magnitude Estimates

   https://doi.org/10.1785/0220250419  

   Trugman, Daniel T; Ben-Zion, Yehuda (March 2026, Seismological Research Letters)

   Abstract Moment magnitude Mw is derived from seismic moment and was defined with the intent to be a consistent measure of earthquake size. Here, we demonstrate that reported Mw values depend systematically on the rigidity structure assumed in the moment tensor inversion, which varies between regions and users. We perform regional moment tensor inversions for 70 target earthquakes in the Walker Lane and southern California regions of the western United States, comparing magnitude results across a suite of commonly used 1D velocity models. Inversions performed with slower, lower rigidity velocity models produce lower Mw estimates than inversions performed with faster, higher rigidity velocity models: the epistemic uncertainty from the choice of velocity model averages ±0.08 for the analyzed earthquakes, with larger uncertainties for shallower events. Using magnitudes based on seismic potency (Mp) instead of Mw can reduce this uncertainty by a factor of 2–3. We introduce a potency-based magnitude Mpv that, by correcting for both the rigidity at source depth and characteristic rigidity of the velocity model, produces a robust magnitude scale that is independent of the velocity model. This formulation can be used to generate uniform and consistent regional and global earthquake catalogs necessary for a wide range of applications in earthquake science and engineering. 

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4. Preliminary Observations of the 5 April 2024 Mw 4.8 New Jersey Earthquake

   https://doi.org/10.1785/0320240024  

   Boyd, Oliver S; Barnhart, William D; Bourke, James; Chapman, Martin; Earle, Paul S; Huang, Guo-chin Dino; Thompson_Jobe, Jessica A; Kim, Won-Young; Link, Frederik; Litherland, Mairi; et al (October 2024, The Seismic Record)

   Abstract On 5 April 2024, 10:23 a.m. local time, a moment magnitude 4.8 earthquake struck Tewksbury Township, New Jersey, about 65 km west of New York City. Millions of people from Virginia to Maine and beyond felt the ground shaking, resulting in the largest number (>180,000) of U.S. Geological Survey (USGS) “Did You Feel It?” reports of any earthquake. A team deployed by the Geotechnical Extreme Events Reconnaissance Association and the National Institute of Standards and Technology documented structural and nonstructural damage, including substantial damage to a historic masonry building in Lebanon, New Jersey. The USGS National Earthquake Information Center reported a focal depth of about 5 km, consistent with a lack of signal in Interferometric Synthetic Aperture Radar data. The focal mechanism solution is strike slip with a substantial thrust component. Neither mechanism’s nodal plane is parallel to the primary northeast trend of geologic discontinuities and mapped faults in the region, including the Ramapo fault. However, many of the relocated aftershocks, for which locations were augmented by temporary seismic deployments, form a cluster that parallels the general northeast trend of the faults. The aftershocks lie near the Tewksbury fault, north of the Ramapo fault. 

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5. 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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