The earthquake activity and strong earthquake risk analysis of Wuzhong-Lingwu region

Based on the existing seismic activity data, past moderate-strong earthquake cases and the foregoing researches in Wuzhong-Lingwu area, this paper summarizes the moderate-strong earthquake sequence, the seismic activity before the mainshock and temporal and spatial features of major earthquakes in mainland China. Characteristics of small and moderate earthquake activity are analyzed based on minimum magnitude of completeness during 1970—2019. The generalized foreshock of moderate-strong earthquake and the small-moderate earthquake activity have many marked features. It reveals that 1 to 2 years before moderate-strong earthquakes, the regional earthquake concentration with M_L≥2.0 was formed in the Wuzhong-Lingwu area and its vicinity. The signal earthquake with M_L≥3.0 mostly appeared in the AzuoqiYaoba area which is in the northwest of Wuzhong-Lingwu area. The generalized foreshock was actually abundant before mainshock occurred, existing some degree of earthquakes intensify. Statistical analysis of the earthquake sequence shows that the multiple mainshock type, double-shock type and swarm type take a greater proportion and the multiple conjugate tectonics is probably the main reason. Besides, from large seismic situation perspective, the leading factor of most previous moderate-strong earthquake with M≥5 is probably caused by strong earthquakes active period of the North China block, and the high earthquake risk of the area has close connection not only with local special tectonic and regional foreshock activity, but also with the effect of major earthquakes activity from North China block to Northeast Asia block. In comparison, the major earthquakes activity of Tibetan plateau, Longmenshan fault zone, Qilianshan structure belt and other areas have no obvious effect on triggering moderate-strong earthquake in Wuzhong-Lingwu area, and there may be tectonic response between moderate-strong earthquake in Wuzhong-Lingwu area and major earthquakes activity from North China block to Northeast Asia block.