本文分析了2012年唐山4.8级地震前,震中附近出现的短期原地重现线状集中分布地磁日变化感应电流异常的时空变化特征,及其与地震、中-下地壳和上地幔高导层的关系,进一步证实了短期原地重现线状集中分布感应电流的走向与中-下地壳和上地幔高导层顶面界埋深走向一致,认为其机理可能是深部热流体的上涌导致壳幔高阻体出现带有上拱性质的拆离滑动,深部上涌的热流体和高导层内热流体侵入高导层内电阻相对较高的地区,高导层出现短时间高导电流通道,当地磁日变化感应电流扫描经过高导电流通道时,感应电流会呈线状集中分布于此,并基于趋肤效应分布于其顶面附近。由于重现异常是发生在震源下方中-下地壳和上地幔高导层的地震异常,且该异常不同于震源附近及其震源至地表的地震异常,因此对推进地震孕育与发生机理研究可能有一定作用。此外研究还发现,地震虽然主要位于重叠段的端部,但更有可能位于中-下地壳重叠段的端部,这一发现对日常震情跟踪中应用该异常确定未来地震位置有一定帮助。

This paper analyzes the temporal and spatial variation characteristics of the short-term in-situ linear concentrated distribution of geomagnetic diurnal variation induced current anomaly near the epicenter before the Tangshan M_S4.8 earthquake in 2012,as well as its relationship with the earthquake,the middle and lower crust and the upper mantle. We further confirm that the trend of the short-term in-situ linear concentrated distribution induced current is consistent with the buried depth of the top surface of the middle and lower crust and the upper mantle. We believe that in terms of mechanism,the upwelling of deep thermal fluid leads to the separation and sliding of the crust-mantle high resistivity body,and the deep upwelling thermal fluid and the thermal fluid in the high conductivity layer invade the high resistivity area. There exists a short period of high-conductivity circulation channel in the high-conductivity layer. When the induced current of local magnetic diurnal variation scans through the high-conductivity circulation channel,the induced current will be concentrated in a linear distribution,and will be distributed near its top surface based on the skin effect. Considering the recurrence anomaly is the seismic anomaly occurring in the middle-lower crust and upper mantle high conductive layer below the source,we believe that this anomaly is different from the seismic anomaly near the source and from the source to the surface,which may play an important role in promoting the study of earthquake preparation and occurrence mechanism. It is also found that although the earthquake is mainly located at the end of the overlapping section,it is more likely to be located at the end of the overlapping section of the middle and lower crust. This finding is helpful for the application of this anomaly in daily seismic tracking to determine the future seismic location.

P315

中国地震局地震预测研究所基本科研业务专项(2020IEF0503)资助