2017年四川九寨沟Ms7.0地震前区域重力场变化

摘要

利用南北地震带2014-2017年期间的流动重力观测资料,系统分析了区域重力场变化及其与2017年8月8日四川九寨沟7.0级地震发生的关系.结果表明:①区域重力场异常变化与北西西向塔藏断裂和南北向岷江断裂带在空间上关系密切,反映了沿控震断裂在2013-2017年期间发生了引起地表重力变化效应的地壳变形和构造活动.②九寨沟地震前,测区内出现了大空间范围的区域性重力异常,而震源区附近产生了局部重力异常,沿塔藏断裂带形成了重力变化高梯度带,其中,甘肃玛曲、迭部、青海河南蒙古族自治县、四川若尔盖、九寨沟一带重力差异变化达100×10-8m·s-2以上;这些可能反映九寨沟地震前,区域及震源区附近均产生与该地震孕育、发生有关的构造运动或应力增强作用.③九寨沟地震震中位于重力差异运动剧烈的鞍部等值线附近,与断裂走向基本一致的重力变化高梯度带零值线上,这一观测事实进一步佐证了重力场动态变化图像对强震地点预测具有重要的指示意义.%Using the relative gravity data from 2014 to 2017 in the North-South seismic belt,we have systematically analyzed the variation of the regional gravity field and their relation to the occurrence of the Jiuzhaigou Ms7.0 earthquake in 2017.The results show that:① The regional gravity change is closely related to the NWW Tazang fault and NS Minjiang fault in space.It reflects the crustal deformation and tectonic activity that occurred along the fault during 2013 to 2017.② Before Jiuzhaigou Ms7.0 earthquake,regional gravity anomalies in large space range appeared in the survey area,while local gravity anomalies occurred near the seismogenic area,forming a high gradient zone of gravity change along the Tazang fault zone.The difference of gravity is up to 100×10-8m · s-2 in Maqu and Diebu of Gansu,Henan of Qinghai,Zoige and Jiuzhaigou of Sichuan.These may reflect the tectonic movement or stress enhancement related to the occurrence of the earthquake before the Jiuzhaigou earthquake.③ The epicenter of the Jiuzhaigou earthquakes located near the isoline of violent change of gravity,which is the same as the fracture strike.This observation further supports the fact that the dynamic change of gravity field is great significance to the prediction of strong earthquake location.