新疆精河6.6级地震周边地区密度构造、均衡异常以及岩石圈挠曲机理

Crustal structure,isostatic anomaly and flexure mechanism around the Jinghe MS6.6 earthquake in Xinjiang

依据EIGEN-6C4重力模型和ETOPO1高程模型数据,围绕新疆精河6.6级地震展开岩石圈均衡与挠曲机理研究,得到如下结论:(1)震中附近的布格与自由空气重力异常分别为-221和-92mGal(10^-5 m·s^-2),震中位于重力异常高梯度带上;(2)震中周边地区地壳厚度约为50km,密度结构总体变化平缓,东西方向地壳厚度变化较小,但自南向北地壳厚度逐渐变薄,精河6.6级地震初始破裂发生在上中地壳分界面附近;(3)震中附近岩石圈承载的垂向构造应力为20MPa左右,震中位于岩石圈垂向构造应力极大值附近的高梯度带上;(4)地震周边地区岩石圈有效弹性厚度最优解为26km,加载比最优解为F1=1,F2=F3=0,表明该区域岩石圈相对坚硬,且导致岩石圈变形的初始加载全部来自地表.

Based on the data of EIGEN-6C4 gravity model and ETOPO1 elevation model,this paper studied the gravity anomaly,lithospheric isostatic state as well as the flexure mechanism around the Jinghe MS6.6 earthquake in Xinjiang,and reached the following conclusions.(1)We obtained the Bouguer and free-air gravity anomalies according to the above gravity and elevation data.The Bouguer gravity anomaly near the epicenter is about-221 mGal(10^-5 m·s^-2),and the free-air gravity anomaly is about-92 mGal.The epicenter is located in the high gradient zones of the Bouguer and free-air gravity anomaly fields.(2)We inversed the crustal density structures around the Jinghe M S6.6 earthquake using the Bouguer gravity anomaly data.The crustal thickness around the epicenter is about 50 km,and the density stratification structure changes gently as a whole.There is no obvious change in the crustal thickness in the East-West direction,but the crustal thickness gradually thins from south to north.The initial rupture of the Jinghe M 6.6 earthquake occurred near the surface between the upper and middle crusts.(3)We calculated the vertical tectonic stress of the lithosphere using both the Bouguer gravity anomaly data and the ETOPO1 elevation data.The vertical tectonic stress near the epicenter is about 20 MPa,and the one in the surrounding area is positive as a whole.The epicenter is located in the high gradient belt near the maximum of the vertical tectonic stress(about 40 MPa).(4)According to the above free-air gravity anomaly data,we studied the flexure mechanism around the Jinghe MS6.6 earthquake through the gravity admittance method.The optimal effective elastic thickness of lithosphere around earthquake is 26 km,and the optimal loading ratio is F1=1,F2=F3=0,which indicates that the lithosphere in this area is relatively hard,and the initial loading of lithosphere deformation comes from the Earth surface completely.