The similar evolution of seismicity patterns of strong-moderate earthquakes before about M_s8 earthquakes of Qinghai-Tibet block

An M_s8.0 super-strong earthquake occurred in Wenchuan of Sichuan on May 12, 2008. Before the earthquake there appeared large-scale strong-moderate seismicity patterns in Qinghai-Tibet block similar with that before the M_s8.1 earthquake of Kunlun Mountain in November of 2001.According to the analysis and study of distribution and evolution of strong-moderate earthquakes before about M_s8 earthquakes in Chinese Mainland since 1900, we considered: ① There is always a two-stage evolution of seismicity pattern of strong-moderate earthquakes before the M_s8 earthquakes in Qinghai-Tibet block.In the first stage strong-moderate earthquakes occurred along the contact zone of Indian Plate and Qinghai-Tibet block while were calm in the Qinghai-Tibet block.In the second stage, the strong-moderate earthquakes extended into the Qinghai-Tibet block and formed large-scale strong-moderate earthquake belts. Subsequent main shock always occurred in the intersection of main or multi-group belts of strong-moderate earthquakes.②The evolution maybe reflects the dynamic-change process of large-area crustal movement and tectonic stress field caused by the action of Indian Plate on Qinghai-Tibet block, which have important significance in M_s≥8 super-strong earthquakes prediction of Qinghai-Tiber block and reference value for prediction of M_s≥8 earthquakes in Xinjiang block, but not valid for earthquakes in the east of Chinese mainland.③ We may find the precursory information before strong earthquakes by studying large-scale evolution of seismicity patterns of strong-moderate earthquakes, which is meaningful and feasible to analyze and forecast future M_s8 earthquakes.In addition, we discussed preliminarily the seismogenic process of Wenchuan earthquake and formation mechanism of large-scale strong-moderate seismicity belts in this paper.