Characteristics of recent tectonic stress field in Jiashi, Xinjiang and adjacent regions

Introduction The Pamirs region where Jiashi is located is one of the most active regions of continental plate dynamics in China. Frequent earthquakes here, especially several strong earthquakes oc- curred in 1997 and 2003, have provided excellent conditions for studying the tectonic stress field in this region and a large number of results (GAO and WEN, 2000; GAO et al, 2004; XU, 2001; ZHOU et al, 2001) have been obtained. Although different methods and data were used, under- standings …

Characteristics of recent tectonic stress field in Jiashi, Xinjiang and adjacent regions

In this paper, we analyze the general directional features of regional tectonic stress field in Jiashi, Xinjiang and adjacent regions from the data of focal mechanism solutions, borehole breakouts and fault slip. The direction of maximum horizontal principal stress given by these three sorts of stress data differs slightly, which indicates there is a NS-trending horizontal compression in the tectonic stress field in the region of interest. We also invert and analyze the temporal and spatial changes of recent tectonic stress field in the research region by using 137 focal mechanism solutions. The inverted results show that the maximum principal stress σ ₁ in Jiashi and adjacent regions is NNW-SSE with an azimuth of 162°. In the period from 1997 to 2003 before the occurrence of Jiashi-Bachu earthquake, the directions of the maximum principal stress σ ₁ and the minimum principal stress σ ₃ in Jiashi seismic source zone changed clockwise with respect to the tectonic stress field in the regions around. The maximum principal stress σ ₁ adjusted to the direction of NNE-SSW with an azimuth of 25°. Under the control of this tectonic stress field, a series of earthquakes happened, including the Jiashi strong earthquake swarm in 1997. Then, the tectonic stress field in the Jiashi seismic source zone might adjust again. And the tectonic stress field controlling the Jiashi-Bachu earthquake in 2003 was in accordance with the regions around. Contribution No. 2006A002, Institute of Crustal Dynamics, China Earthquake Administration.