Background stress state estimated from 2008 Wenchuan earthquake sequence

A model of the tectonic stress state of Longmenshan Faults and adjacent area including direction and magnitude is derived from the spatial and temporal distribution of seismicity before and after Wenchuan M(s)8.0 earthquake. This technique utilizes the assessment of spatial correlationship between stress change and seismicity change to obtain stress information. One detailed source models derived from the inversion of body wave, geology field survey and GPS data was used to calculate the stress change field from the Wenchuan mainshock, which was fit to the spatial distribution of seismicity. Agreement between the best-fitting background stress state from seismicity modeling and the background stress state inferred from focal mechanisms was found to be consistent, showing that the spatial distribution of seismicity contains information about the stress state. The best fitting background stress state has its greatest principal compressive stress plunging 11 degrees to N295 degrees W, a large effective coefficient of friction 0.76 for Longmenshan area, and 75 MPa for the magnitude of greatest principal stress, which is far less than the overburden pressure estimated from the pressure intact rock endured in 15 km depth. Although the estimations of the magnitude of background stress, gradient of stress with depth and effective coefficient of friction are quite uncertain, and need further research to confirm, the result provides the dynamic information of stress loading on the Longmenshan Faults, which is useful for the further research on seismogenic stress environment.