In this paper, numerical computations are carried out to investigate the seismo-electromagnetic signals arising from the motional induction effect due to an earthquake source embedded in 3-D multi-layered media. First, our numerical computation approach that combines discrete wavenumber method, peak-trough averaging method, and point source stacking method is introduced in detail. The peak-trough averaging method helps overcome the slow convergence problem, which occurs when the source–receiver depth difference is small, allowing us to consider any focus depth. The point source stacking method is used to deal with a finite fault. Later, an excellent agreement between our method and the curvilinear grid finite-difference method for the seismic wave solutions is found, which to a certain degree verifies the validity of our method. Thereafter, numerical computation results of an air–solid two-layer model show that both a receiver below and another one above the ground surface will record electromagnetic (EM) signals showing up at the same time as seismic waves, that is, the so-called coseismic EM signals. These results suggest that the in-air coseismic magnetic signals reported previously, which were recorded by induction coils hung on trees, can be explained by the motional induction effect or maybe other seismo-electromagnetic coupling mechanisms. Further investigations of wave-field snapshots and theoretical analysis suggest that the seismic-to-EM conversion caused by the motional induction effect will give birth to evanescent EM waves when seismic waves arrive at an interface with an incident angle greater than the critical angle θ_c = arcsin(V_sei/V_em), where V_sei and V_em are seismic wave velocity and EM wave velocity, respectively. The computed EM signals in air are found to have an excellent agreement with the theoretically predicted amplitude decay characteristic for a single frequency and single wavenumber. The evanescent EM waves originating from a subsurface interface of conductivity contrast will contribute to the coseismic EM signals. Thus, the conductivity at depth will affect the coseismic EM signals recorded nearby the ground surface. Finally, a fault rupture spreading to the ground surface, an unexamined case in previous numerical computations of seismo-electromagnetic signals, is considered. The computation results once again indicate the motional induction effect can contribute to the coseismic EM signals.

在本文中，通过数值计算来研究由嵌入在 3-D 多层介质中的地震源引起的运动感应效应产生的地震电磁信号。首先，详细介绍了我们结合离散波数法、峰谷平均法和点源叠加法的数值计算方法。峰谷平均法有助于克服缓慢收敛问题，当源接收器深度差异很小时会出现这种问题，允许我们考虑任何聚焦深度。点源叠加法用于处理有限断层。后来，发现我们的方法与曲线网格有限差分法在地震波解中具有很好的一致性，这在一定程度上验证了我们方法的有效性。此后，气固两层模型的数值计算结果表明，地表下方的接收器和地表上方的接收器都会记录到与地震波同时出现的电磁（EM）信号，即所谓的同震。电磁信号。这些结果表明，先前报道的由悬挂在树上的感应线圈记录的空中同震磁信号可以用运动感应效应或其他地震-电磁耦合机制来解释。对波场快照的进一步研究和理论分析表明，当地震波以大于临界角的入射角到达界面时，由运动感应效应引起的地震到电磁波的转换将产生倏逝电磁波。θ _c  = arcsin( V _sei / V _em )，其中V _sei和V _em分别是地震波速度和电磁波速度。发现计算出的空气中的 EM 信号与理论上预测的单一频率和单一波数的幅度衰减特性具有极好的一致性。源自电导率对比的地下界面的倏逝 EM 波将有助于同震 EM 信号。因此，深度处的电导率将影响地表附近记录的同震电磁信号。最后，考虑了传播到地表的断层破裂，这是先前地震电磁信号数值计算中未经检验的情况。计算结果再次表明运动感应效应对同震电磁信号有贡献。