Focal Mechanism and Tectonic Stress Field in Hebei and Its AdjacentArea

Using the CAP method,we calculated the focal mechanism solutions of the M_L≥3.5 earthquakesoccurred from January 2008 to November 2013 in Hebei province and its adjacent area. Most of the focal mechanisms are of strike-slip fault type except for a certain number of normal faults. The maximum principal compressive stress axis of the tectonic stress field is in the NEE direction which is consistent with previous research results, but the tectonic stress field shows a transient normal fault and strike-slip stress state and has the characteristics of inheritance and difference. These characterizes may be related to the aspects that moderate earthquake is easily affected by the regional tectonic activities and the changing of regional tectonic stress field caused by great earthquake.