Stress disturbance around Xianshuihe fault zone in the eastern Qinghai–Tibet Plateau and implication for fault stability

Abstract

The Xianshuihe fault zone in the eastern Qinghai–Tibetan Plateau is an important active tectonic boundary. Understanding its stress state is important for characterizing the dynamic evolution of the Qinghai–Tibet Plateau and the mechanism of the frequent occurrence of large earthquakes. Using 30 years of in-situ stress data from the Xianshuihe active fault zone, we statistically analyzed the spatial distribution characteristics of the stress in the region. The study area is generally characterized by a strike-slip stress field. Nevertheless, the stress state is vulnerable to topography and shows high spatial variation near the Earth’s surface at a depth of 0–400 m. The local stress near the fault zone varies from the far-field stress. The orientations of the maximum horizontal principal stress possess an elliptical shape around the fault zone, while its magnitudes become hump-like as the distance increases from the fault. The large difference in properties between the fault zone and its adjacent rocks contributes to the differentiation of the direction of the local stress field near the fault. The results allow us to formulate a preliminary hypothesis that a rigid lateral extrusion model may control the nonuniformity of the local stress field in the Xianshuihe fault zone and preferentially interpret the tectonic uplift of the southeastern margin of the Qinghai–Tibet Plateau. Further, the stress accumulation in the shallow crustal regions of the Xianshuihe fault zone is relatively high, indicating that some segments of the fault zone are critically unstable. Kangding area (the Zheduotang segment and the Yalahe segment) and Luhuo segment hold relatively high potential for large earthquakes. The results of this study are of great significance for revealing the mechanism of fault–stress field interactions and for understanding the dynamic evolution mechanism of the uplift of the Qinghai–Tibet Plateau.