华北地区GPS地壳应变能密度变化率场及其构造运动分析

A STUDY ON ANNUAL ACCUMULATION OF STRAIN ENERGY DENSITY SIGNIFICANCE BY USING GPS MEASUREMENTS IN NORTH CHINA

利用GAMIT软件将华北地区GPS地壳形变监测网 1 995、1 996及 1 999年 3期观测数据同全球IGS跟踪站资料进行了统一处理 ,并采用基线向量单天解及其全协方差矩阵和武汉大学PowerAdjVer3 .0软件在ITRF97框架下进行了GPS网整体平差 ,得出了相对于欧亚板块的水平运动速度场 ;进一步利用GPS速度场计算华北地区GPS地壳应变率场及应变能密度变化率场 .GPS结果表明 :华北地区现以 (3— 1 2mm/a)± 3 .4mm/a速度相对于稳定的欧亚板块向东或东南方向运动 ;唐山—河间—磁县是一个压缩活动边界 ,大同—太原则是一拉张活动边界 ,呈略带右旋的拉张运动 ;北京—天津—渤海湾地区 ,以及邢台地区是高剪应变率地区 ;张家口—北京—天津—渤海湾地区 ,以及济南地区是高应变能密度变化率地区 ,地壳积累能量高 ,且渤海湾地区处于面膨胀变化率正、负值过渡带 ,那里可能存在与地震危险性有关的应变能积累背景 .

Global Positioning System (GPS) data in three measurement campaigns from 1995 to 1999 are used to study tectonic activity and earthquake hazards in North China. These GPS data were firstly processed together with the data from 13 Global IGS stations using the GAMIT software to get the baseline solutions. Then GPS velocity field in north China with respect to Eurasia was obtained in ITRF97 frame based on these baseline solutions and their variance covariance matrix using the GPS network adjustment software Power ADJ developed by Wuhan University. Using the GPS velocity field, we estimate the annual accumulations of strain rate field and strain energy density field. These fields show that (1) Most stations move eastward or southeastward at a rate of (3-12mm/a)± 3.4 mm/a with respect to Eurasia. (2) Tangshan-Hejian-Xingtai is an active seismotectonic compression border. Datong-Taiyuan is an active extension border with slight dextral rotationl; (3) Beijing-Tianjing-Bohai and Xingtai regions are higher shear strain rate region. Zhangjiakou-Beijing-Tianjin-Bohai and Jinan regions exhibite higher annual accumulation of strain energy density than other regions in North China, showing more amount of the energy storage. The Bohai region is also located in exchanging zone for positive to negative surface strain rate, it maybe the earthquake risk region in the future.