It is reported that earthquakes are accompanied by electromagnetic (EM) anomalies. These anomalies are thought to be caused by earthquakes but their generation mechanism is still unclear. The piezoelectric effect has been proposed as a possible mechanism, particularly in quartz-rich rocks. However, the EM responses to earthquakes due to such an effect have not been well understood. In this article, we study the EM signals generated by an earthquake source due to the piezoelectric effect. We develop a semi-analytical method to simulate the EM responses to earthquake sources in a 3-D layered model and conduct numerical simulations to investigate the characteristics of the EM fields. The results show that the piezoelectric effect in quartz-rich rocks could be the responsible mechanism for the EM signals recorded during the earthquake. Two kinds of EM signals can be generated by the earthquake, namely, the early EM wave arriving before the seismic waves and the coseismic EM field accompanying the seismic waves. For an M_w 6.1 earthquake, the coseismic electric field is ∼0.1 μV/m and the magnetic field can only reach ∼10⁻⁵ nT. We also study the sensitivity of the coseismic EM fields to the rock conductivity. The results indicate that the coseismic EM fields are mainly affected by the conductivity of the shallow layer where the receiver is located, and if the top layer is thin, they are also affected by the conductivity of the deeper layer due to the contribution of the evanescent EM wave created at the interface.

中文翻译：

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由于“∞m”对称性压电效应对地震源电磁响应的数值模拟

据悉，地震伴随着电磁（EM）异常。这些异常被认为是由地震引起的，但其产生机制仍不清楚。压电效应被认为是一种可能的机制，特别是在富含石英的岩石中。然而，由于这种效应而导致的电磁对地震的响应尚未得到很好的理解。在本文中，我们研究了地震源由于压电效应而产生的电磁信号。我们开发了一种半解析方法来模拟 3D 分层模型中地震源的电磁响应，并进行数值模拟以研究电磁场的特征。结果表明，富含石英的岩石中的压电效应可能是地震期间记录的电磁信号的机制。地震可产生两种电磁信号，即先于地震波到达的早期电磁波和伴随地震波的同震电磁场。对于M _w 6.1地震，同震电场为∼0.1 μV/m，磁场只能达到∼10 ^-5  nT。我们还研究了同震电磁场对岩石电导率的敏感性。结果表明，同震电磁场主要受接收器所在浅层电导率的影响，如果顶层较薄，由于倏逝波的贡献，同震电磁场也会受到较深层电导率的影响。在界面处创建电磁波。