Surface creep differences and affecting factor along the Xianshuihe fault zone in response to the Wenchuan and Lushan earthquakes

Abstract

As the southwest and southeast boundaries of the Bayan Har block, the Xianshuihe Fault Zone (XSHFZ) and the Longmenshan Fault Zone (LMSFZ) are likely to be intrinsically related in terms of tectonic activity. Consequently, it is pertinent to consider the potential response of fault creep in the XSHFZ when the LMSFZ encounters different major earthquake disturbances. This paper presents a comparative and analytical study of the fault creep characteristics of the XSHFZ, employing cross-fault short-baseline survey data collected prior to and following the Wenchuan M8.0 and Lushan M7.0 earthquakes. The findings indicate that despite the Wenchuan earthquake having a significantly higher magnitude than the Lushan earthquake and the theoretical static stress change being considerably larger than that of the Lushan earthquake, the absolute velocity and incremental change of fault creep in the XSHFZ before and after the Wenchuan earthquake are less pronounced than those observed before and after the Lushan earthquake. Following the Wenchuan earthquake, the creep rate and nature of the XSHFZ remained largely unchanged, with a slight decrease in the average slip rate. However, in the aftermath of the Lushan earthquake, the XSHFZ exhibited clear signs of "activation," with a notable increase in the average creep rate and the emergence of strong tensional motion. It is hypothesized that the Maerkang, Miyaluo, Minshan, and Huya Fault Zones within the Longmenshan sub-block contributed to the increased complexity of the strong earthquake process, potentially acting as a 'regulating valve' in influencing the redistribution of post-seismic stress and the creep pattern of adjacent faults. Consequently, their roles in regional tectonic activity cannot be overlooked.