基于断层虚位错模式分析2015年内蒙古阿左旗MS5.8地震前地电阻率变化

doi:10.12196/j.issn.1000-3274.2022.02.007

摘要/Abstract

摘要： 2015年4月15日内蒙古阿拉善左旗发生M_S5.8地震, 震中300 km范围内存在4个地电阻率观测台。其中, 距离震中约67 km的宁夏石嘴山台地电阻率NW45°(NW)向自地震发生前1年开始出现年变幅减小的低值破年变现象, 且该测向与地震最大主压应力轴方位近于垂直。本文通过褶积拟合分析, 发现该变化与降雨和气温的变化无关; 计算地电阻率归一化月速率显示, 自2014年1月开始, 归一化月速率出现快速下降, 7-12月超过了异常阈值-2.4, 到震前又快速恢复, 这与众多震例研究结果一致; 基于断层虚位错模型, 模拟了震前震中附近面应变和主应变的变化, 发现石嘴山台处在压缩区, 且受到NE向挤压。而其他无变化的台站均位于面应变影响范围以外, 与岩石物理实验中应力挤压引起地电阻率呈现下降变化的结果一致。因此, 石嘴山台地电阻率的异常变化很可能是阿左旗地震前区域应力变化的反映。

关键词: 石嘴山地震台, 地电阻率, 虚位错模式, 各向异性, 2015年阿左旗M_S5.8地震

Abstract: There were 4 apparent resistivity stations operating within 300 km of the epicenter of the 15 April 2015 AlxaZuoqi M_S5.8 earthquake. A phenomenon that the annual variation decreased with low values was found in the Northwest direction of Shizuishan station berfore the earthquake, and the direction of resistivity is nearly perpendicular to Axis azimuth of seismic maximum principal compressive stress. In this paper, by convolution fitting, it was found that the change was independent with the rainfall and temperature. The result calculated by normalized monthly variation rate methods showed that the rapid descent change have started from January in 2014 and beyond the anomalies limit of -2.4 from July to December, this result was consistent with many earthquake case studies. In order to calculate the stress-strain distribution before the AlxaZuoqi earthquake, a fault virtual dislocation model was adopted in this paper. The calculated result showed that Shizuishan station was located in the extrusion zone, which is consistent with the results of apparent resistivity decreased caused by stress extrusion in rock physics experiments. Therefore, the change of apparent resistivity in Shizuishan station was probably a reflection of the regional stress variation before the 2015 Azuoqi M_S5.8 earthquake.

Key words: Shizuishan statio, Apparent resistivity, Fault virtual dislocation model, Anisotropy, the 2015 AlxaZuoqi M_S5.8 earthquake

中图分类号:

P315

李新艳, 曾宪伟, 卢军, 马禾青, 崔瑾, 卫定军. 基于断层虚位错模式分析2015年内蒙古阿左旗M_S5.8地震前地电阻率变化[J]. 地震, 2022, 42(2): 89-99.

LI Xin-yan, ZENG Xian-wei, LU Jun, MA He-qing, CUI Jin, WEI Ding-jun. Anomalies of Apparent Resistivity Before the 2015 AlxaZuoqi M_S5.8 Earthquake in Inner Mongolia of China Based on Fault Virtual Dislocation Model[J]. EARTHQUAKE, 2022, 42(2): 89-99.

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