The Tectonic Stress Tensor of Ms 8.0 Wenchuan Earthquake from Fault Slip Data and Coseismic Displacement

摘要

The seismogenic structure of the Ms 8.0 Wenchuan earthquake is the Longmenshan fault zone. Itsrnsurface rupture occurs mainly on the Yingxiu-Beichuan fault and the Guanxian- Jiangyou fault,rnespecially the former with the lengths of 240 km. By field investigation and observation, therngeometrical characteristics and the spatial distribution of the tectonic stress tensor show that thernsurface rupture along the Longmenshan fault zone has segmented characteristics. The surface rupturesrnon the southwest subsegment of Yingxiu-Beichuan fault and on the Guanxian-Jiangyou fault arerndominated by reverse-slip faulting, but on the northeast subsegment of Yingxiu-Beichuan fault isrncharacterized with comparable horizontal and vertical motion. In addition, the results inverted fromrnfault slip data measured by field work and from coseismic displacement both indicate that the recentrntectonic stress field along Longmenshan fault is characterized by two different types of tectonic stressrntensors. One is reverse-slip and the direction of the maximum compressional stress is nearly in EWrndirection. The other is strike-slip but with comparable vertical component, and the direction ofrnmaximum principal stress is also in EW direction. Though the two types of tectonic stress tensorsrnhave different stress regime, they both indicate that the characteristics of the recent tectonic stressrnfield along the Longmenshan fault is dominated by near E-W maximum compressional dynamicrnenvironment.