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Study on the ULF Magnetic Field Generated by Earth Currents Relating to Large EQs
Radio Science ( IF 1.6 ) Pub Date : 2021-04-13 , DOI: 10.1029/2019rs006992
H. Zhou 1, 2 , F. Yan 1 , J. Wang 1, 2 , Q. Luo 1, 2 , T. Jin 1, 2
Affiliation  

ULF magnetic anomalies (f < 1 Hz) have been observed prior to multiple large earthquakes (EQs) during the last three decades. A polarization analysis method was produced and applied in many EQ cases in order to discriminate the weak ULF crustal signals from other signals. Although many publications considered the parameter of polarization ratio (amplitude or power ratio of vertical magnetic field component to horizontal components), a key parameter in the polarization analysis method, useful to detect the possible magnetic signals associated with EQs, there were also many doubts on its reliability. The aim of this work is to evaluate the possibilities of the polarization ratio increases prior to large EQs based on the prevail assumption of Earth currents as the source of ULF emissions during the early stage of EQ preparation independent of the mechanism involved in producing the currents, and the parallel 3‐D finite‐difference time‐domain technique is applied to calculate the electromagnetic responses in the whole inhomogeneous Earth‐ionosphere waveguide. The contributions of the lightning discharges on ULF power are also evaluated based on the gridded flash counts included in the Lightning Imaging Sensor climatology data. The results reveal that the surface vertical magnetic field and polarization ratio are possible to increase locally around the epicenters as long as the intensity of the surface seismic magnetic fields are large enough compared with those produced by other sources. Unfortunately, the actual increases are usually difficult to be distinguished obviously mostly due to the weak seismic increases.

中文翻译:

与大EQ有关的地电流产生的ULF磁场的研究

ULF磁异常(f 在过去的三十年中,在多次大地震(EQ)之前已观察到<1 Hz)。产生了一种极化分析方法,并将其应用于许多EQ情况,以便将弱ULF地壳信号与其他信号区分开。尽管许多出版物都考虑了极化比参数(垂直磁场分量与水平分量的振幅或功率比)的参数,这是极化分析方法中的关键参数,可用于检测与均衡器相关的可能的磁信号,但也存在许多疑问。其可靠性。这项工作的目的是基于在EQ准备的早期阶段,将地球电流作为ULF排放源的普遍假设,独立于产生电流的机制,来评估大EQ之前极化比率增加的可能性,并采用并行3D时域有限差分技术来计算整个非均匀地球电离层波导中的电磁响应。雷电放电对ULF功率的贡献也基于闪电成像传感器气候数据中包含的栅格化闪光计数进行评估。结果表明,只要与其他震源相比,地表地震磁场的强度足够大,地表垂直磁场和极化率就有可能在震中附近局部增大。不幸的是,通常由于地震增加较弱,通常很难区分出实际的增加。
更新日期:2021-04-22
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