Characteristics of the seismic source stress field in the joint region of Xianshuihe, Longmenshan and An(ninghe faults

Twenty-two earthquakes (ML=2.2~3.7) in the joint region of Xianshuihe, Longmenshan and An(ninghe faults are studied in this paper. The source mechanism solutions of these events are obtained using P-wave first motion method, and the characteristics of the source stress field and rupture in the joint region are summarized preliminarily with some results of other researchers. Being strongly extruded by the approximately horizontal regional stress with the direction from north-west to south-east and the effect of the complex tectonics in the region, the source stress field has complex and variable characteristics. The earthquakes mainly show normal or strike-slip faults in Yajiang, North-triangle and west of Chengdu-block areas, indicating that the vertical forces have been playing an important role in the source stress fields, while the earthquakes mainly show reverse or strike-slip faults in Baoxing-Tianquan area, with the horizontal components of the principal pressure stress axes identical to the south-west direction to which the shallow mass is moving. We think that the manifold combinations of earthquake faults are the micro-mechanism based upon which the large regional shallow crust mass has been moving continually.