Characterization of the Solution of the Seismic Source Mechanism in Southeastern Sichuan

Southeastern Sichuan has witnessed intensified seismic swarm activity since 2016, including events exceeding historical peak ground accelerations. This study integrates moment tensor solutions, stress field inversion, and Mohr–Coulomb analysis to investigate the interplay between tectonic processes and shale gas extraction in driving seismicity. Full-waveform moment tensor inversions of 118 earthquakes (M ≥ 3.5) reveal predominant double-couple mechanisms (62% with DC > 70%), with minor non-double-couple components linked to fluid-induced volume contraction. Stress field inversions demonstrate spatial heterogeneity: Region A (south) exhibits a counterclockwise-rotated maximum horizontal stress direction compared to Region B (north), which aligns with the regional NW-SE tectonic compression. Mohr’s circle analysis highlights distinct failure regimes—40% of the events in Region A fall below the failure threshold (pore-pressure-influenced), while 60% in Region B exceed it (stress-dominated). These findings underscore the combined roles of tectonic inheritance (NE-SW basement faults) and anthropogenic perturbations (fluid injection) in modulating seismic hazards.