Abstract: It is well known that clustered small earthquakes often happen around the fault plane of large earthquakes.Based on simulated annealing algorithm and Gauss-Newton methods,using precisely located small earthquakes between January 2009and June 2015 which happened near the 2012and 2013 M_S4.8earthquake epicenters in Xinfengjiang Xichang,we get detail parameters and geography of two intersecting faults.The length of NEE fault plane(F1)with right lateral strike slip is about 8.2km.Its strike is 78.5°and dip is 87.7°.The length of NW fault plane(F2)with left lateral strike slip is about 5.9km. Its strike is 137.3°and dip is 87.9°.The inversion results proved to be correct by the focal mechanisms of M_L≥3earqaukes.At last,causative structures of the two M_S4.8earthquakes are determined by their focal mechanisms.

Key words: Seismic fault, Focal mechanism, Inversion, Xichang earthquakes