Abstract:
focal parameters of the small earthquakes occurred in Guanzhong and Shaannan region from Sep.2001 to Jun. 2002 are determined with digital records, and the source spectra as well as the character of ambient stress distribution are analyzed. The result show that the ambient shear stress is lower in Guanzhong and Shaannan region, between 3.3×10
5~32.2×10
5Pa, but the western part (12×10
5~32×10
5Pa) is higher than the eastern part(8×10
5~17×10
5Pa), the central part is lowest. There are two higher region in west part, one is Baoji, Meixian, Fengxiang and its surrounding region, 20×10
5~32×10
5Pa, another is Liuba, Fengxian and its surrounding region, 20×10
5~37×10
5Pa. The higher region in eastern part is Gaoling, Yaoxian, Sanyuan and its surrounding region, 16×10
5~18×10
5Pa. An
MS4.8 earthquake occurred in Jingyang of the region on Jan 5, 1998.