Middle-small Earthquake Relocation and Tectonic Characteristics of Tangshan and Its Adjacent Area

In this study, we relocated 4 115 earthquakes occurred during January 2009 to October 2015 in Tanshan and its adjunct area using the double-difference methods, analyzed the relationship between the distribution of earthquakes and the active faults. The results show that the earthquakes mainly concentrate in the northern of the North China plain and most intensively focused on Tangshan seismic region. Earthquakes epicenters concentrated along faults and presented the characteristics of banding distribution. Most of the depth of earthquake source distributed between 5 and 15 kilometers with the variant depth distribution feature to different seismic belt. The earthquake seismogenic layer is middle-upper crust in Zhangjiakou-bohai seismic belt, while it is upper crust in Bohai sea seismic belt. The earthquake source depth of Zhangjiakou-Bohai seismic belt showed the trend of gradually becomes shallow from west to east, and there is a small earthquake activity belt in north east direction and steep dip angle on the east side of Tangshan fault belt.