Contemporary deformation and earthquake hazard of the Capital Circle of China inferred from GPS Measurements

The Capital Circle (CC) is a region with high risk of great damaging earthquake hazards. In our present study, by using a subset of rigorously GPS data around the North China Plain (NCP), med-small recent earthquakes data and focal mechanism of high earthquakes data covering its surrounding regions, the following major conclusions have been reached: (a) Driven by the deformation force associated with both eastward and westward motion, with respect to the NCP, of the rigid South China and the rigid Amurian block, widespread sinistral shear appear over the NCP, which results in clusters of parallel NNE-trending faults with predominant right-lateral strike-slips via bookshelf faulting within the interior of the NCP. (b) Fault plane solutions of recent earthquakes show that tectonic stress field in the NCP demonstrate overwhelming NE-ENE direction of the maximum horizontal principal stress, and that almost all great historical earthquakes in the NCP occurred along the NWW-trending Zhangjiakou-Bohai seismic belt and the NNE-trending Tangshan-Hejian-Cixian seismic belt. Additionally, We propose a simple conceptual model for inter-seismic deformation associated with the Capital Circle, which might suggest that two seismic gaps are located on the middle part of Tangshan-Hejian-Cixian fault seismic belt (Tianjin-Hejian segment) and the northeast part of Tanlu seismic belt (Anqiu segment), and constitute as, in our opinion, high risk areas prone to great earthquakes.