Dynamic Images of Stress Field during Genesis and Occurrence of the 2006 Wen'an Earthquake

Through digital seismic waveform data,the focal-mechanism solutions of the ML≥2.0 earthquakes in Hebei region are inversed.The analysis of the solutions shows that the dominant orientation of stress axial is completely consistent with that of the tectonic stress field of North China.This phenomenon indicates that the focal-mechanism solutions are restricted by the dynamic factors in a large-scale area.The consistent parameters of the focal mechanism solutions are calculated and spatially interpolated and their characteristics of spatial dynamic variation before the 2006,MS5.1,Wen'an Earthquake are got.The result showed that a larger area with the low value of the consistent-parameters appeared around the focal region before the Wen'an Earthquake,and it expanded gradually along with time.This phenomenon might be a dynamic precursor of the medium-strong earthquake.