Xu Zhang

The heterogeneous coupling distribution on subduction interface not only influences the slip distribution of megathrust earthquakes but also plays a critical role in facilitating intraplate strike-slip events. On 16 July 2025, an Mw 7.3 strike-slip earthquake struck the Shumagin segment of the Alaska Peninsula, raising questions about its seismogenic fault orientation and mechanical origin. Using artificial intelligence-enhanced detection and relocation of the seismic sequence, we constructed an east–west trending, south-dipping, curved seismogenic fault model. Joint inversion of teleseismic waveforms and Global Navigation Satellite System data reveals a predominantly sinistral strike-slip mechanism, and the rupture was confined largely beneath the subduction interface, indicating that it is an intraplate event. Together with the nearby 2020 Mw 7.6 dextral strike-slip earthquake, the two events form a conjugate fault system. We demonstrate that both earthquakes, though differing in strike direction, can be explained by the stress perturbations arising from along-strike and along-dip variations in megathrust coupling, acting in concert with the background stresses from slab pull and plate bending. These findings underscore the widespread influence of coupling heterogeneity in influencing strike-slip earthquake generation in subduction zones and call for a reassessment of related seismic hazards in regions such as the Semidi segment.

SUMMARY: The 2020 MS 5.0 Qiaojia earthquake occurred in a tectonically complex region near the Xiaojiang fault in southwestern China. We investigated the rupture process of this moderate-sized earthquake using a multi-empirical Green’s function (EGF) inversion method that integrated waveforms from multiple EGF events. Synthetic tests demonstrated that the multi-EGF inversion method recovered the input model more robustly than any individual EGF inversion. The resolved spatiotemporal rupture model of this earthquake indicated a compact rupture lasting approximately 2.9 s, dominated by a major asperity near the hypocentre and characterized by predominantly eastward rupture propagation. Bootstrap resampling analyses further confirmed the robustness of the resolved major coseismic slip distribution and the overall moment release pattern. We also observed a spatial complementarity between the coseismic slip and aftershock distributions, with most aftershocks clustering around the periphery of the major asperity. This study not only elucidates the source complexity of the 2020 MS 5.0 Qiaojia earthquake, but also validates the robustness and effectiveness of the multi-EGF inversion method in resolving the rupture processes of moderate-sized earthquakes. Our results provide new insights into the rupture kinematics of moderate-sized earthquakes and the heterogeneity of fault strength and stress within the Xiaojiang fault zone and its surrounding regions.

Investigating aircraft accidents is a critical and challenging endeavor in the field of aviation safety. Current practices in seismology-based air accident investigations focus on locating crash sites to aid in the search and recovery of missing aircraft. In this study, we conducted an analysis of the China Eastern Airlines Boeing 737–800 crash on 21 March 2022, by leveraging three-component seismic records acquired from a location 21 km away from the crash site, in conjunction with publicly available radar data from Flightradar24 (an online service). Our approach helps to reconstruct the flight state of the aircraft at the time of the impact by modeling the dynamics of the impact with the Earth’s surface. Through an inversion process, we successfully obtained the force–time function and determined the direction of the impact force. In addition, we conducted inquiries into the weight of the 737–800 airliner, which enabled us to estimate the speed of the aircraft at the time of the accident to be about 200–264 m/s using the momentum theorem. These results are in agreement with time of the last radar signal and the measured dive angle of the airplane, providing valuable insights into the circumstances surrounding the crash.

The 2008 M_w7.9 Wenchuan earthquake ruptured the middle and northeastern segments of the Longmenshan Fault Zone (LMSFZ), and the 2013 M_w6.6 Lushan earthquake ruptured a 50km-long fault in the southwestern segment. Subsequently, an M_w5.8 earthquake occurred approximately 10 km distant from the Mw6.6 Lushan earthquake. Therefore, the potential risk for larger earthquakes (>Mw6.6)on the southwestern section must be considered. This study collects the latest seismological and GPS data to construct an integrated seismotectonic model for the two neighboring earthquake sequences. The model integrates the fault planes involved, the mainshock rupture processes, the mainshock-caused Coulomb stress perturbation, the aftershock distribution and the 3-D velocity structure of the source region, providing information for seismic risk evaluation. We find that three fault planes were involved, two of which were related to the mainshocks, and the third was generated by the aftershocks following the first mainshock. The mainshocks were caused by nearly pure thrust faulting on the two planes with dip angles of approximately 45° and almost opposite dipping directions, thereby forming a conjugate angle of around 90°. The third plane was located between the two mainshocks, approximately parallel to the second mainshock's fault plane. Each of the mainshocks primarily ruptured a single asperity, displaying simple time history. The Coulomb stress change of the first mainshock facilitated the generation of the second mainshock and the third fault plane, and the second mainshock increased the stress on the first mainshock's fault plane. The aftershocks were distributed within stratified materials by spatially varying interfaces and characterized by high Vp and Vs velocity and a low Vp/Vs ratio. The atypical dip angles of approximately 45° for thrust faults and the conjugate angle of approximately 90° are indicative of high stress state. The single asperity rupture implies simple stress accumulation. The mainshock-caused Coulomb stress change did not reduce the seismic risk in the source region. The varying interfaces are interpreted as a consequence of long-term horizontal compression. All of these characteristics suggest that the two earthquake sequences were generated by the breakage of three immature faults under strong compression by background stress, and the high stress state remains within the southwestern LMSFZ.

Combined with the multi‐array back‐projection and finite‐fault joint inversion methods, we investigate the detailed spatiotemporal rupture complexity of the 2021 M_W 7.4 Maduo earthquake using seismic and geodetic data. Our results reveal that this earthquake ruptured bilaterally 170 km long fault segments with a duration of 38 s. The obtained back‐projection results, specific aftershock signature of the supershear earthquake, and observations of far‐field Love Mach waves consistently validate that this earthquake is a supershear event. Furthermore, by analyzing global large strike‐slip earthquakes, we find that the moment‐scaled radiated energies of previously well confirmed supershear earthquakes with relatively simple fault geometries are similar to that of the 2021 M_W 7.4 Maduo earthquake, which are significantly smaller than those of subshear strike‐slip events. This new finding provides additional supporting evidence to validate the supershear rupture during the 2021 M_W 7.4 Maduo earthquake.

On 21 May 2021, an Mw 6.1 earthquake, causing considerable seismic damage, occurred in Yangbi County, Yunnan Province of China. To better understand the surface deformation pattern, source characteristics, seismic effect on nearby faults, and strong ground motion, we processed the ascending and descending SAR images using the interferometric synthetic aperture radar (InSAR) technique to capture the radar line-of-sight (LOS) directional and 2.5-dimensional deformation. The source model was inverted from the LOS deformation observations. We further analyzed the Coulomb failure stress (CFS) transfer and peak ground acceleration (PGA) simulation based on the preferred source model. The results suggest that the 2021 Yangbi earthquake was dextral faulting with the maximum slip of 0.9 m on an unknown blind shallow fault, and the total geodetic moment was 1.4 × 10¹⁸ Nm (Mw 6.06). Comprehensive analysis of the CFS transfer and geological tectonics suggests that the Dian–Xibei pull-apart basin is still suffering high seismic hazards. The PGA result demonstrates that the seismic intensity of this event reached up to VIII. The entire process from InSAR deformation to source modeling and strong ground motion simulation suggests that the InSAR technique will play an important role in the assessment of earthquake disasters in the case of the shortening of the SAR imaging interval.