Abstract
<title>Abstract</title> <p>Seismic activity at Vietnam’s Song Tranh 2 (ST2) reservoir represents a globally significant case of persistent reservoir-triggered seismicity (RTS), spanning over 14 years since impoundment in 2010. We apply an integrated physics-based ETAS framework to 8,273 events, combining 3D Coulomb stress changes, anisotropic pore pressure diffusion, and fault interaction laws to decouple four core seismogenic components. Inversion results at a 5.5-km depth reveal that natural tectonic background seismicity dominates (63.59%), confirming the reservoir acts as an external hydraulic trigger releasing pre-accumulated endogenous energy within the Kon Tum block. Fault-to-fault stress interaction accounts for 27.10%, driving the sequence's multi-year persistence, while pore pressure inflation and elastic loading contribute 8.07% and 1.24%, respectively. Notably, a strong basement hydraulic anisotropy is validated, with vertical diffusivity exceeding the horizontal component by a factor of 11.29. This designates steep-dipping northwest-southeast (NW-SE) faults as highly conductive fluid conduits transporting fluids to hypocentral depths within 48 days. Furthermore, 3D geomechanical modeling establishes an optimized regional stress field (σ_1=320^°), explaining epicenter clustering along the NW-SE corridor. This framework also resolves the mechanism of fluid-driven reactivation along stable faults, demonstrating that fluid pressure reduces the frictional threshold to promote failure despite a low initial slip tendency (T_S≈0.36). These findings provide a robust quantitative platform for seismic hazard assessment and risk mitigation globally.</p>