Geometric pattern and active tectonics in Southeastern Gansu province: Discussion on seismogenic mechanism of the Minxian-Zhangxian MS6. 6 earthquake on July 22, 2013

Southeast Gansu province along the central-northern portion of the South-North Seismic Belt, the tectonic activities and deformation pattern are closely related to the northeastward growth of the Tibetan Plateau. Complicated structural geometries were controlled by both Eastern Kunlun and West-Qinling Northern Faults, and outward growth of the NE Tibet continuously contributes to the regional active deformation. In recent years, intermediate-strong earthquakes occurred frequently, calling for a detailed analysis. By integrating both structural and historical seismicity studies, and combining geophysical, seismological and field investigations, we conclude that northward indenting and eastward movement along the Eastern Kunlun Fault is the main tectonic stress source, and also it provides the basic setting and mechanism to generate strong earthquakes. Left-lateral slip and its bi-flanking thrusting 'flower structure' of the West-Qinling Northern Fault contributed to the frequent occurrence of intermediate-strong earthquakes along the Lintan-Tanchang fault to the south. Minxian-Zhangxian M(S)6. 6 earthquake on July 22, 2013 along the central-eastern Lintan-Dangchang fault is a consequence of differential activity due to heterogeneous segments.