2020年唐山古冶5.1级地震前后岩石圈磁场异常变化分析

Variation of lithospheric magnetic field anomalies before and after the Guye, Tangshan MS5.1 earthquake in 2020

摘要:

基于唐山及周边地区2019年9月—2021年4月连续4期流动地磁观测资料,获得唐山地区岩石圈磁场异常变化模型,以此分析2020年7月12日唐山古冶5.1级地震前后半年期岩石圈磁场的时空变化特征。结果表明:(1)岩石圈磁场变化的水平矢量在地震前出现明显的方向转向和幅值弱化的现象,地震前后经历了“由震中向周边分散由周边向震中汇聚发震方向反转”的时空演化过程;(2)震中附近各测点岩石圈磁场总强度值在地震前后具有规律性时序变化,均呈现“震前缓慢减小同震时期急剧增大震后急剧减小”的特征;(3)基于压磁效应和断层亚失稳模型分析,地震前后岩石圈磁场异常的时空变化特征或许是由震中附近主要断裂地应力的积累和释放所致。

Abstract:

Based on the mobile geomagnetic data of Tangshan and its adjacent areas obtained from September 2019 to April 2021, we construct the variation model of the lithospheric magnetic field anomaly in the Tangshan area and analyze the spatiotemporal variation characteristics of the lithospheric magnetic field before and after the Guye M_S5.1 earthquake on July 12, 2020. The results show the following: (1) There is a shift in the direction of the horizontal lithospheric magnetic field variation and an obvious decrease in its amplitude before the earthquake; before and after the earthquake, the lithospheric magnetic field experiences a spatiotemporal evolution process of “dispersing from the epicenter to the peripherygathering from the periphery to the epicenterreversing its direction.” (2) The total intensity of the lithospheric magnetic field at measurement points near the epicenter varies regularly in time and sequence, exhibiting the characteristic of “slowly decreasing before the earthquakesharply increasing during the coseismic periodsharply decreasing after the earthquake.” (3) Based on the piezomagnetic effect analysis and the meta-instability model of the fault, we consider that the spatiotemporal variation of the lithospheric magnetic field anomalies before and after the earthquake is caused by the accumulation and release of the in-situ stress of the main faults near the epicenter.