Temporal variations in magnetic signals generated by the piezomagnetic effect for dislocation sources in a uniform medium
Temporal variations in magnetic signals generated by the piezomagnetic effect for dislocation sources in a uniform medium
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DOI：
10.1093/gji/ggw125
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发表时间：
2016-03
影响因子：
2.8
通讯作者：
K. Yamazaki
中科院分区：
文献类型：
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作者：
K. Yamazaki
地壳中的断层破裂产生弹性波和电磁波。如果能够观测到相应的电磁信号，那么就可以在第一波地震波到达之前检测到地震。在这项研究中，我认为压磁效应作为一种机制，将弹性波转换为EM能量，我推导出转换过程的解析公式。在这项研究中考虑的情况是一个全空间模型，其中弹性和电磁性能是均匀的和各向同性的。在这种情况下，弹性场和电磁场的控制方程，结合压磁本构律，可以在时域中解析求解，忽略位移电流项。利用导出的公式，数值例子进行了研究，并解决了相应的预期的磁信号的特性。我表明，磁场的时间变化强烈依赖于介质的电导率，这意味着精确检测压磁效应产生的信号通常是困难的。对于矩震级≥ 7.0的地震，在震源距离为25 km时，压磁信号的预期振幅估计不大于0.3 nT;然而，这一结论可能不会扩展到真实的地震的检测，因为压磁应力敏感性目前受到的约束很差。
Fault ruptures in the Earth’s crust generate both elastic and electromagnetic (EM) waves. If the corresponding EM signals can be observed, then earthquakes could be detected before the first seismic waves arrive. In this study, I consider the piezomagnetic effect as a mechanism that converts elastic waves to EM energy, and I derive analytical formulas for the conversion process. The situation considered in this study is a whole-space model, in which elastic and EM properties are uniform and isotropic. In this situation, the governing equations of the elastic and EM fields, combined with the piezomagnetic constitutive law, can be solved analytically in the time domain by ignoring the displacement current term. Using the derived formulas, numerical examples are investigated, and the corresponding characteristics of the expected magnetic signals are resolved. I show that temporal variations in the magnetic field depend strongly on the electrical conductivity of the medium, meaning that precise detection of signals generated by the piezomagnetic effect is generally difficult. Expected amplitudes of piezomagnetic signals are estimated to be no larger than 0.3 nT for earthquakes with a moment magnitude of ≥ 7.0 at a source distance of 25 km; however, this conclusion may not extend to the detection of real earthquakes, because piezomagnetic stress sensitivity is currently poorly constrained.