| The Shanxi-Hebei-Inner Mongolia border region locates the junction of Shanxi and Zhangjiakou-Bohai seismic zone. Because of the importance of its geographical position and particularity of its structure, distribution of seismic station continued to be more intensive,the small and medium earthquakes’ information was recorded more completed,which provide reliable and rich data,the research of tectonic stress field in the study area has very important scientific significance for regional dynamics.This dissertation is based on the 490 earthquakes’ travel time and waveform dataform 2010 to 2014 in study area and composed of two parts:Using 5216 P wave arrival times of 490 eathquakes, we calculated the 1-D P wave velocity model and station correction value by the minimum 1-D velocity model method, the travel time residuals was significantly reduced after relocation, the station correction value represents the lateral heterogeneity of surface velocity structure.It shows that the model is stable and reliable, which lay the foundation for the study on stress field.Using the result of new eathquake locations and velocity model after relocation, and recalculating the azimuth and off-source angle of 3413 first motion of Pwave,we obtained the orientation of stress field by the composite focal mechanism method. The main types of the composite focal mechanism are normal and slip, the strike of nodal planes is consistent with the strike of main faults on two sides of the basin, T-axis is generally perpendicular to strike of these faults, P-axis change from NE to NEE,then nearly EW in study from west yo east.Compared with previous research, this research used data richer and newer, based on the thenew eathquake locations and velocity calculated the 0.25° ×0.25°stress field on detail. The stress directions show that the source of the stress field in this area is driven by the India plate and Pacific plateto Eurasian plate extrusion. |
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