Moment Tensor Inversion of Moderate Earthquakes and the Locally Perturbed Stress Field in the Jiashi Source Region

Abstract

AbstractMoment tensors of 52 moderate sized earthquakes occurred in Jiashi source region, Xinjiang, from 1997 to 2004 were determined in time domain by using the long period waveforms recorded by regional broadband stations. The results demonstrate significant variations of the orientation and plunge of P, T and N axis from west to east in the source region. Therefore, we further divided the whole region into two parts, which are called the western part and the eastern part, and performed the stress tensor inversion respectively. The results show that in the eastern part, the maximum principal axis σ1 is almost horizontal and trends N321°E, the minimum principal axis σ3 trends 68° with a plunge of 40°, and σ2 trends 213°; with a plunge about 40°;. Till 2004, the stress within the western part remains stable, with the σ1 and σ3 nearly horizontal and trending to N12°E and N282°E respectively, the middle axis σ2 almost vertical. Thus the maximum principal stress σ1 significantly rotates counter clockwise from N10°E in the west part to N39°W in the east part across the whole studied region. Compared with the stress field in the eastern part, the western part is under a stronger horizontal extension effect. This lateral perturbation of stress field is consistent with the pattern of crustal deformation rate from GPS observation, as well as the topography map at the structure boundary between Tarim basin and Tienshan. We infer that both the sharp deformation in the deep crust and the large‐scale NNW trending Puchang and Selibuya fault structures may play a crucial role in resulting in the local stress perturbation pattern.