Influence of stress changes caused during the coseismic and postseismic periods of the 2008 Wenchuan MS 8.0 earthquake on May 12th on the MS 4.1 earthquake in the Xiangxi area of the three Gorges reservoir on November 22, 2008

Abstract

To investigate the seismic hazards caused by large earthquakes around the Three Gorges Reservoir (TGR), we calculate the postseismic quasistatic Coulomb failure stress (CFS) and the coseismic dynamic changes in the CFS generated by the Wenchuan earthquake (WCE, mainshock) on May 12, 2008(WCE), in the TGR area. For the coseismic dynamic CFS changes, the results show that in the first few minutes after the WCE, the seismic waves spread to the Xiangxi earthquake (XXE) area in the Xiannvshan fault (XNF) zone on November 22, 2008.The dynamic change in the CFS generated in the XNF zone was positive, with a peak value of 1.32 MPa. This result indicates that the coseismic dynamic change in the CFS generated by the WCE made the rocks in the XNF zone more susceptible to fracturing and weakening, which may have triggered the XXE in the TGR. The results reveal that the postseismic quasistatic CFS changes were positive and increased with depth, reaching approximately 0.05KPa at the epicenter before the XXE, resulting in the quasistatic change in the CFS generated by the WCE on the XNF surface. The postearthquake quasistatic change in the CFS exhibited a small positive value, indicating that shear stress had been continuously applied on the fault plane to promote sliding of the fault plane, which may have had a certain impact on the fault rupture. This study has practical importance for analyzing the seismic hazards of large earthquakes near the TGR and the earthquake resistance and defense of the TGR area.