3D geomechanical modeling of the Xianshuihe fault zone, SE Tibetan Plateau: Implications for seismic hazard assessment

Abstract

The Xianshuihe fault on the southeastern margin of the Tibetan Plateau is one of the most active intracontinental faults worldwide. At least 16 strong earthquakes (M > 6.5) have occurred on this fault since 1327 CE. To reasonably assess the future seismic hazard of this fault region, it is essential to gain a comprehensive knowledge of the fault kinematics and stress state. In this study, we developed a fine 3D geomechanical model of the Xianshuihe fault and its adjacent area, and obtained a spatially continuous contemporary kinematics and crustal background stress field of this region. Our modeled results show that the slip rate of the Xianshuihe fault is as high as 11 mm/a on the northwestern segment and generally decreases to ~9 mm/a on the southeastern segment (i.e. Moxi fault). The Yulongxi fault, a branch oblique to the Moxi fault, has different slip senses in different segments with a very low horizontal slip rate (<0.6 mm/a). In terms of stress, the study area is dominated by a transtensional faulting stress regime with E-W-trending maximum horizontal stress SH, indicating the study area is mainly subjected to an E-W compression and N-S extension. Localized normal and thrust faulting regimes appear alternately along the Xianshuihe fault, showing an inhomogeneous stress state. The high normal stresses on the Songlinkou-Selaha segment and the Moxi fault combined with their relatively high slip rates, make us speculate that these two segments have the potential to produce strong earthquakes in the future. A relatively high seismic hazard is also ascribed to the Yulongxi fault based on the analysis of its geological and geodynamic environment.