【摘要】 自1975年以来,海城附近发生具有一定规模和强度的震群(ML≥4.0;震次≥100次)有:1975年2月4日海城7.3级、1999年11月29日岫岩5.4级、2008年11月14日海城ML4.8和2012年2月2日盖州ML4.8震群,这4个震群发生前地震活动背景怎样,是否存在着某种共同的特点?对这4个震群进行对比研究发现:震前1年该区出现小震群活动,ML≥3.0地震条带、地震活动水平明显增强,连续发生多次ML≥4.0地震,ML≥4.0地震震源机制高度一致,且震中最近台站记录P波初动符号出现明显的一致性等变化,可视为地震异常。及时捕捉中强地震前异常,对于地震活动趋势判断起到至关重要的作用。更多还原

【Abstract】 There are 4 earthquake swarms which are ML≥4.0 and shock times ≥100 happened near Haicheng since 1975:Haicheng 7.3 magnitude earthquake in February 4,1975,Xiuyan 5.4 magnitude earthquake in November 29,1999,Haicheng ML4.8 earthquake in November 14,2008 and Gaizhou ML4.8 earthquake in February 2,2012.We conduct a comparative study on the seismic activity background of these 4 earthquake swarms.We found that small earthquake swarms occurred 1 year before the main shock,ML≥3.0 earthquake strip and seismicity level enhanced significantly,multiple ML≥4.0 earthquakes with unanimous focal mechanism occurred consecutively,P wave first motion symbol of nearest station in epicenter showed apparent consistency.We consider all these phenomena as seismic anomalies.Catching the seismic anomalies in time before strong earthquakes can do great contribution to the judgment of seismic activity trend.更多还原