2017年四川九寨沟MS7.0地震震前地壳密度变化特征

基于紧凑约束最小二乘优化反演算法，利用2014~2017年地表重力变化观测成果，反演得到2017年九寨沟MS7.0地震前震中及周边地区的地壳三维密度变化。结果表明：1）在震中及周边地区出现大范围的重力变化，并沿张掖-西宁-九寨沟一带形成最大值达9 μGal的重力变化梯度带；2） 地壳密度变化量随深度增加而增大，其中在45 km附近达到最大，为0.2 g/cm3；3） 震中及邻区范围内形成密度变化的正负四象限分布（2014-04~2017-04），其表现的物质运移方向呈左旋走滑式分布，与震源机制解基本一致。据此推断，在震前产生了与地震孕育相关的深部构造运动，而强震易发生在物质运移汇聚地方。

Density Variation in the Crust before the Jiuzhaigou,Sichuan, MS7.0 Earthquake of 2017

We obtain the density variation in the crust from the Jiuzhaigou MS 7.0 earthquake in 2017, deriving it from the dynamic variation of gravity in 2014~2017, using the compact gravity inversion method: (1) before the Jiuzhaigou MS7.0 earthquake, variation of gravity in the large space range appears in the survey area, while forming a high gradient zone of gravity change along the Zhangye-Xining-Jiuzhaigou; (2) the density variation in the crust increases with depth, and is up to 0.2 g/cm3 at 45 km depth around; (3) during the early period before the MS7.0 Jiuzhaigou earthquake (2014-04~2017-04), regional density variation is distributed in a four-quadrant form. The materials migration is dominated by left-lateral strike motion, which is same as the focal mechanism solutions. The results show the tectonic movement related to the occurrence of this earthquake before the Jiuzhaigou earthquake, and that strong earthquakes occur easily in places where material migration is concentrated.