宁夏地区GPS监测网建设、近期地壳运动特征及应力场与地震活动关系初探

Establishment of the GPS Monitoring Network in the Middle Part of Ningxia and Preliminary Study of Relationship between the Crustal Deformation and the Stress Field and Seismicity

在阿拉善块体、鄂尔多斯块体和青藏块体交汇处的宁夏中部布设了GPS观测网 ,利用 1996年以来的 5期复测资料 ,分析了宁夏中部地区现今地壳运动状态 ,其结果为 :①宁夏中部地区在 1996年 12月至 1999年 5月间 ,有围绕鄂尔多斯西缘 (P2测点 )左旋运动的现象 ,银川盆地东侧的灵武断裂呈左旋逆走滑运动方式。该区主应力场方向为北北东 -南南西 (方位角为2 9 8°)方向 ,P2测站以南的中部地区向东位移 ,垂直形变量级明显大于水平形变量级 ,银川盆地及青藏块体呈上升状态 ,鄂尔多斯腹地的P1测站呈逐年下降趋势 ,在P3与P4测点间可能有一隐伏断裂存在。②在GPS测区附近中强地震前约 1年 ,可观测到该区GPS测站的形变异常及主应力方向发生转变异常 ;测区附近中强地震前及周边地区强震前 ,该区GPS形变模拟矢量场能够预示未来地震的大体方位。这些结果可作为地震预测的特征值加以考虑。

The GPS observation network has been established by the Seismological Bureau of Ningxia Hui Autonomous Region which is located at the junction zone of Alashan block,Ordos block and Qinghai\|Xizang(Tibet)block in the middle part of Ningxia. Based on the 5 times' observation data of GPS after 1996,the crustal movement has been analyzed in this region. The results are obtained as follows: ① the middle area of Ningxia has showed the case of left circumgyrating around the west edge of Erdos(P2) from December 1996 to March 1997. The Lingwu fault of eastern edge of Yinchuan basin has showed as being thrust fault with left strike slip. The direction of principle stress is NNE-SSW (azimuth 29.8°). The vertical deformation is larger than horizontal deformation with an obvious eastward displacement by the affect of stress in this area. There is an insidious fault between the P3 and P4 station perhaps. The P1 station in the center of Ordos has a sinking trend by year; ②The deformation abnormity for GPS stations and the change of maximal principle stress direction are observed by GPS survey before the moderately strong earthquake occurred near this area around one year. The vector map of GPS deformation can show the direction of earthquake in the future. The eigenvalue can be tried in earthquake prediction in this area.