Background stress state estimated from 1996 Lijiang earthquake sequence
利用1996年丽江地震序列反演震区应力状态

Estimates of the tectonic stress state including direction and magnitude of principal stress are derived from the regional seismicity before and after 1996, MS7.0 Lijiang earthquake. This technique was originally applied to the Landers aftershock sequence (Gross and Kisslinger, 1997). Two kinds of input include a combined catalogue of events before and after the Lijiang earthquake, and a source model derived from the inversion of body wave. The stress field in source region was calculated using a 3-D dislocation model, and the best stress state is statistically determined by evaluating the relativity between stress change and seismicity change. The result shows that the azimuth of maximum principal stress in 10 km depth is 355 degree, and the magnitude of maximum principal stress is 53MPa, which is much smaller than the value estimated from the intact rock at that depth. Inversions for the best fitting background stress state are consistent with focal mechanism solution (with a 12 degree difference). This study shows that the spatial distribution of seismicity can present stress state information of source area. 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 faults, which is useful for the further research on stress environment of seismogenic area.