Analysis on statistic characteristics of seismic gap in Chinese mainland

By searching seismicity gap patterns in 5 study regions with the same procedure, we obtained appearance of gap before 194 earthquakes from a relatively complete catalogue of 367 Mge;5.0 earthquakes in Chinese mainland. The ratios of the earthquakes with gap over total studied earthquakes in different regions are 14:36 for northern China, 21:24 for southeastern China, 68:124 for Sichuan and Yunnan region, 36:82 for the northern Qingzang Plateau, and 55:101 for Xinjiang region, respectively. The region with lowest gap ratio before studied earthquakes is the northern China, and that with highest ratio is the southeastern China, the ratios of Xinjiang region and Sichuan province are nearly equal. Based on the above, we discussed statistic relation between the mainshock occurrence after the gap formation and the lasting time of the gap, gap scale, and the earthquake magnitude forming gaps. The result shows that there exists certain correlation between the gap lasting time, gap scale and mainshock magnitude, but the error is large. The gap threshold magnitude for M5 mainshock is ML2.5 or so, the threshold magnitude for M6 mainshock is ML3.5 or so, and the threshold for M 7 earthquake is aboutML4.0, and the mainshocks are usually located on gap verge or outside. The gap ratio before ML5,M6 and M7 earthquakes are 46%、73% and 100%, respectively.