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Yongqing Zhang, Institute of Crustal Dynamics, China Earthquake Administration (China)
Furen Xie, Institute of Crustal Dynamics, China Earthquake Administration (China)
Susanna Gross, Cooperative Institute for Research in the Environmental Sciences, University of Colorado (United States)
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Estimates of the tectonic stress state including direction and magnitude are derived from the spatial and temporal distribution of Lijiang aftershock sequence and compared with the inversion result with focal mechanism solution data. This technique was originally applied to the Landers aftershock sequence[Gross and Kisslinger, 1997] and based upon the seismicity model of Dieterich [1994], which suggests that the number of aftershocks in an area should be proportional to the stress step experienced in that area. Two kinds of input needed: a combined catalogue of events before and after the strong or large earthquake, and a source models derived from the inversion of body wave or geodetic data, the stress field in source region was calculated using a 3D dislocation model, and statistically determined a best stress field such that the relativity between stress change and seismicity change is most significant. We inverted stress state (during 1991 to 1998 in Lijiang and adjacent area using this method, the result shows that: the azimuth of maximum principal stress in 10km depth is 331 degree, and the magnitude of maximum principal stress is 53MPa, which is about one fifth of overburden pressure estimated from the pressure intact rock endured in 10km depth. Inversions for the best fitting background stress state are consistent with fits of focal mechanism solution (only with a 12 degree difference), but estimations of the magnitude of background stress, gradient of stress with depth and effective coefficient of friction are quite uncertain, they need further research to confirm.
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