GRAVITY VARIATION BEFORE AND AFTER THE MS5.4 EARTHQUAKE IN CANGWU IN 2016

doi:10.3969/j.issn.0253-4967.2018.03.003

Abstract

Abstract: Based on the mobile gravity observation data in 2014-2016 in Guangxi and its adjacent areas, this paper systematically analyzed the changes of regional gravity field and its relation to the M_S5.4 Cangwu, Guangxi earthquake on July 31, 2016, and combined with GPS observation data and seismic geological survey results, discussed the temporal and spatial distribution characteristics of the changes of regional gravity field and its mechanism. The results show that:(1) Before and after the M_S5.4 Cangwu earthquake, the gravity anomaly changes near the earthquake area were closely related to the major faults in space, which reflects the crustal deformation and tectonic activities that caused the surface gravity change along the seismogenic fault in the period of 2014-2016; (2) The gravity changes near the epicenter before and after the M_S5.4 Cangwu earthquake showed an evolution process in which the positive gravity anomaly zone changed to the negative gravity anomaly zone, a gravity gradient belt appeared along NNE direction and the earthquake occurred in its reverse change process; (3) The epicenter of the M_S5.4 Cangwu earthquake located both near the gravity gradient belt and in the zero transition zone of the surface strain gradient and the edge of the high maximum shear strain rate area, the observational fact further proved that the dynamic image of gravitational field and deformation field have important instruction significance to the location prediction of strong earthquakes; (4) in recent years, the gravity dynamic change in northwestern Guangxi presented a four-quadrant distribution pattern, and there is the risk of generating earthquake of magnitude about 5 in the center of the quadrants.

Key words: M_S5.4 earthquake in Cangwu, gravity field, deformation field, seismic risk

摘要： 利用广西及邻区2014—2016年流动重力观测资料，系统分析了区域重力场变化及其与2016年7月31日广西苍梧M_S5.4地震的关系，并结合GPS观测数据与地震地质调查成果，探讨了区域重力场变化的时空分布特征及其机理。结果表明：1）苍梧M_S5.4地震前后，震区附近重力异常变化与主干断裂在空间上关系密切，反映了沿控震断裂在2014—2016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）苍梧M_S5.4地震前后震中附近的重力变化，是1个由重力正值异常区向重力负值异常区变化，沿NNE向出现重力变化梯度带，并在变化过程中发震的演化过程；3）苍梧M_S5.4地震震中既位于重力变化梯度带附近，也处于面应变梯度带零值过渡区和最大剪应变率高值区的边缘部位，这一观测事实进一步佐证了重力场和形变场动态变化图像对中强地震地点预测具有重要的指示意义；4）近期桂西北地区重力动态变化图像呈现四象限分布的特征，四象限中心地带存在发生中强地震的危险。

关键词: 苍梧M_S5.4地震, 重力场, 形变场, 地震危险性

CLC Number:

P315.72⁺6

ZHOU Bin, WEN Xiang, YUAN Yong-dong. GRAVITY VARIATION BEFORE AND AFTER THE M_S5.4 EARTHQUAKE IN CANGWU IN 2016[J]. SEISMOLOGY AND GEOLOGY, 2018, 40(3): 539-551.

周斌, 文翔, 原永东. 2016年苍梧M_S5.4地震前后重力变化[J]. 地震地质, 2018, 40(3): 539-551.

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