Seismotectonic analysis of the December 2023 MS6.2 Jishishan earthquake: Insights from high-resolution DEM, aftershock relocation, and fault modeling

The December 18, 2023, M S 6.2 Jishishan earthquake occurred along the northeastern margin of the Qinghai-Xizang Plateau within the Laji–Jishi Shan Fault Zone (LJSFZ), a complex thrust-dominated tectonic belt. To identify the seismogenic fault and better understand the regional tectonic framework, we integrated high-resolution Digital Elevation Models (DEMs) derived from GF-7 stereo satellite and Unmanned Aerial Vehicle (UAV) photogrammetry, relocated aftershock sequences, and conducted detailed field investigations. Our results identify four Late Quaternary thrust faults (F1-1 to F1-4), among which the Zhaomuchuan fault (F1-3), a NE-dipping back-thrust, aligns closely with the mainshock and aftershock distribution and exhibits clear Holocene activity. Seismic relocation reveals a NE-dipping seismogenic zone at depths of 5–12 km, consistent with a shallow reverse-faulting mechanism under WSW–ENE oblique compression. Structural analysis and cross-sectional profiles suggest that fault F1-3 propagates into a mid-crustal detachment surface, forming a foreland-vergent thrust-nappe system. Importantly, the rupture of this secondary fault, rather than the locked primary boundary fault F1-1, indicates stress transfer and localization within a critically tapered wedge, consistent with global analogs of back-thrust-dominated earthquakes. These findings underscore the seismotectonic complexity of the LJSFZ and highlight the significant seismic hazard posed by subsidiary structures in compressional settings.