Characteristics of Source Rupture of the Jiashi Xijiang Strong Earthquake Swarm in 1997

Abstract

AbstractIn 1997, a series of major earthquakes including events of MS ≥3.6 occurred in Jiashi area, Xinjiang of china. It is a rare intraplate seismic swarm. Using GDSN (Global Digital Seismic Network) broadband P wave records and first motion direction of primary wave in short period records from the regional seismological network, we have investigated the focal mechanism and the rupture process of the these earthquakes. The results show that the focal mechanisms of the Jiashi events include two types of strike‐slip and normal faulting. Their Common feature is that the principal compression stress is in NNE direction and the principal extension stress is in NW direction. They are different from the regional tectonic stress field as evidenced by geological data and indicate a local character. The source rupture characteristics show that the slip scales, the rise times, and the rupture times of the finite fault are relatively small. And the source rupture area is also small, which spread from one point toward all directions without dominant extension. The rupture planes of the Jiashi events are in NE direction, coincident with the gradient belts of focal depths and crustal deformation, and isoseisms and spreading directions of earthquakes, The Jiashi earthquakes are caused by several times of brittle failure in NE direction under the tension‐shear stress, which is formed by laterally nonhomogeneous deformation in the left strike‐slip and normal faulting.