2019年丰南4.5级地震前后岩石圈磁场水平矢量动态演化特征

Dynamic Evolution of Horizontal Vector of Lithospheric Magnetic Field Before and After the 2019 Fengnan MS4.5 Earthquake

摘要:

基于唐山及周边地区2018年4月—2020年9月连续6期的流动地磁观测资料,经过数据处理获得5期岩石圈磁场半年尺度的时空变化数据,再结合2019年12月5日丰南4.5级地震对震中附近岩石圈水平矢量时空演化特征进行分析。结果表明: ①在岩石圈磁场水平矢量动态演化过程中,丰南地震震中附近岩石圈磁场水平矢量异常出现在震前一年时期,且随着时间推移,岩石圈磁场水平矢量弱变区在空间上具有由东向西发展的演变过程。②丰南地震震中区域水平矢量模值在地震前后出现先减小后增大的反向变化,震前半年水平矢量模值最小,丰南地震发生于水平矢量模值反向增大的过程中。③根据亚失稳理论与岩石圈磁场水平矢量变化关系,在多期岩石圈磁场水平矢量存在方向变化和弱变的区域寻找潜在的异常区,再结合异常区水平矢量模值的动态演化,或许可以作为一种识别震前震磁前兆异常信息的方法。

Abstract:

Based on six consecutive periods of mobile geomagnetic observation data in Tangshan and its surrounding areas from April 2018 to September 2020,the spatial and temporal variation data of the lithospheric magnetic field on a half-year scale were obtained through data processing. In conjunction with the Fengnan M_S4.5 earthquake on December 5,2019,the spatial and temporal evolution characteristics of the lithospheric horizontal vector near the epicenter were systematically analyzed. The results indicate that: ①In the dynamic evolution process of the lithospheric magnetic field's horizontal vector,an anomaly in the horizontal vector appeared in the epicenter area of the Fengnan earthquake one year before the event. Over time,the weak variation area of the vertical magnetic field exhibited an east-to-west spatial evolution. ②The magnitude of the horizontal vector in the epicenter area of the Fengnan earthquake decreased initially and then increased before and after the earthquake. The horizontal vector magnitude was smallest six months before the earthquake,with the Fengnan earthquake occurring during the reverse increase of the horizontal vector modulus. ③According to the relationship between the sub-instability theory and the horizontal vector variation of the lithospheric magnetic field,identifying seismomagnetic precursory anomalies may involve searching for potential anomaly areas where the horizontal vector of the lithospheric magnetic field shows directional and weak variations over multiple periods. This should be combined with the dynamic variation of the average value of the horizontal vector modulus in the anomaly area. These findings suggest a method for identifying seismomagnetic precursor information before an earthquake by monitoring specific variations in the horizontal vector of the lithospheric magnetic field.