2008年汶川8．0级地震前川青块体及邻区地震活动性分析

本文简要分析了2008年5月12日汶川8．0级地震前川青块体及邻区的地震活动性特征。结果表明，汶川地震发生的龙门山断裂本身历史地震活动水平不高，其周边的鲜水河断裂、岷江断裂、虎牙断裂等历史上强震多发；汶川8．0级地震前龙门山断裂带3级以上中小地震活动增强或平静异常现象不明显，地震活动参数值均在正常变化区间内；4级以上地震异常平静，形成了地震空区；2007年底到2008年初位于龙门山断裂带及其附近台站的0．1级以上小震月频度增强明显。

Seismicity analysis on the Qinghai-Sichuan Blocks and proximity before the 2008 Wenchuan M8.0 Earthquake

The seismicity characters of the Qinghai-Sichuan Blocks and proximity before the 2008 Wenchuan M8.0 Earthquake are summarized.Analyzing results show that the active level of historical earthquakes along the Longmenshan faults is not high and a lot of strong earthquakes occurred along following faults:Xianshuihe,Mingjiang and Huya.The seismicity level of small and moderate magnitude more than M3.0 along Longmenshan Faults increased and these anomalous items were not clear before the 2008 Wenchuan M8.0 Earthquake.The seismicity parameters were in the normal level and the seismicity of magnitude M4.0 earthquakes is quiet.A gap of magnitude M4.0 earthquakes was formed.The active rate of events per month with magnitude more than 0.1 earthquakes increased from 2007 to 2008 before the 2008 Wenchuan M8.0 Earthquake.