2019—2021年门源MS6.9地震岩石圈磁场异常回溯分析

Retrospective Analysis of Lithospheric Magnetic Field Anomalies of Menyuan MS6.9 Earthquake from 2019 to 2021

分析了2019—2021年门源MS6.9地震周边岩石圈磁场部分要素的时空演化特征,结果表明:岩石圈磁场要素异常在震前1~2年比较明显,其中震中均位于磁偏角D模量、总强度F模量、垂直分量Z模量的正负交界地带,距离“0”值线10~50 km,震中位于水平分量模量的高梯度带,水平矢量方向和幅值在震中东南100 km范围内转向、回旋和减小,垂直矢量的方向和幅值在震中及东南100 km范围内出现对冲、发散和减小;震前1~2年水平矢量幅值、垂直矢量幅值在发震断层冷龙岭断裂带东段南北两侧呈现出北高南低的态势,依据压磁效应分析可知,冷龙岭断裂带东段北侧岩石圈磁场较大,应力变化主要以释放为主,南侧岩石圈磁场较小,应力变化主要以加载为主,反之该区域应力场的变化导致了岩石圈磁场的异常变化。

This paper analyzes the temporal and spatial evolution characteristics of some elements of the lithospheric magnetic field around the Menyuan MS6.9 earthquake from 2019 to 2021.The results show that the anomalies of the lithospheric magnetic field elements are obvious 1-2 years before the earthquake,and epicenters are located at the positive and negative boundaries of the magnetic declination D modulus,total strength F modulus,and vertical component Z modulus isolines,10-50 km away from the"0"value line.The epicenters are located at the high gradient zone of the horizontal component modulus,and the direction and amplitude of horizontal vector turn,whirl and decrease within 100 km southeast of the epicenter,while the direction and amplitude of vertical vector diverge and decrease within 100 km southeast of the epicenter.The amplitude of horizontal vector and vertical vector 1-2 years before the earthquake show a trend of high in the north and low in the south on the north and south sides of the east section of the Lenglongling fault zone.According to the analysis of piezomagnetic effect,it can be seen that the lithospheric magnetic field on the north side of the east section of the Lenglongling fault zone is large,and the stress change is mainly release,while the lithospheric magnetic field on the south is small,and the stress change is mainly loading.On the contrary,the change of stress field in this area leads to the change of lithospheric magnetic field.