Distinct tectonic activities in Guangxi, China due to large earthquakes on the Longmenshan fault zone

摘要

It is of great importance to study active tectonics in Guangxi, China which is a region with relatively high level of seismic hazard. In this work, we attempt to apply the Load/Unload Response Ratio (LURR) method to test stress state of tectonic field in Guangxi and find obvious difference in the periods before and after earthquakes on the Longmenshan (LMS) fault zone. The regions with higher stress accumulation indicated by LURR augmented significantly after the 2008 Ms8.0 Wenchuan earthquake and reduced gradually following the 2013 Ms7.0 Lushan earthquake. The movement of LURR was along a northwestern trending strike slip fault, the Bama-Bobai fault, showing the shear loading acting on the fault. To evidence this viewpoint, we construct GPS velocity profile on this fault. Results show that the fault manifested left lateral motion after the Wenchuan earthquake. This movement which, was never observed before the Wenchuan earthquake, faded away after the Lushan earthquake. We suggest that the detected changes, both in LURR and GPS velocity field, were probably caused by stress redistribution on the LMS fault zone due to occurrence of large earthquakes. The results may imply the potential seismic hazard zone in Guangxi.