Implication from the 2023 M_W6.0 Jishishan earthquake: Complex fault structure beneath the Jishi Shan, northeastern Qinghai-Xizang Plateau

Although the Lajishan-Jishishan fault zone is considered as one of the most tectonically active orogenic belts along the northeastern margin of the Qinghai-Xizang Plateau, its present-day slip behavior and subsurface geometry remain poorly understood. The 2023 Jishishan earthquake, accompanied by high-resolution geodetic observations, offers a unique opportunity to advance our understanding of the regional tectonism. In this study, both Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data are used to jointly constrain the coseismic slip distribution associated with the 2023 Jishishan earthquake. Our results suggest that rupture occurred along two distinct fault segments within the Jishishan fault zone: a primary northeast-dipping fault plane and a shallower southwest-dipping subsidiary fault. The inversion results of the double-fault model show a peak slip of 0.40 m on the main fault at a depth of 14.85 km and a peak slip of 0.09 m on the shallow subsidiary fault at 2.35 km depth. This double-fault rupture model is supported by multiple lines of evidence, including geodetic observations, seismological data, and surface fault mapping. The derived coseismic slip model sheds new light on the complex fault structure beneath the Jishi Shan, highlighting the possibility of segmented fault geometries and multi-fault interactions. Specifically, the northeast-dipping fault, identified as the Jishishan West Margin Fault Zone (JSSWF), appears to be intersected at depth by a southwest-dipping structure, likely corresponding to the Jishishan East Margin Fault Zone. This intersection may have disrupted rupture propagation, resulting in a discontinuity along the seismogenic fault plane. Notably, the 2023 rupture was confined to the lower portion of the seismogenic layer, leaving the upper segment of the JSSWF unruptured. This remaining strain accumulation in the shallow crust indicates a potentially persistent seismic hazard in the region.