水平分层孔隙介质中点源激发的震电波场数值模拟及分析

为认识地震波诱导的电磁场的特性，本文研究地震波在孔隙介质中由于动电效应引起的电磁场.基于Pride弹性-电磁耦合方程组推导了双力偶震源对应的位移-应力-电磁场间断向量的表达式，模拟了双力偶源激发的震电波场.作为比较，还模拟了爆炸点源激发的震电波场.结果表明：存在伴随纵波的电场，其各分量的波形与固相位移对应分量的波形相似，但相位相反；存在伴随横波的磁场，其波形与固相位移波形相似；双力偶震源还激发出了独立传播的辐射电磁场，其速度比纵波至少高一个数量级，几乎是“瞬间同时”到达了每个接收器，但是其强度比伴随电磁场小得多，且随着源距增大而迅速减小.本文研究还表明：伴随纵波的电场强度不仅与地震纵波幅度和动电耦合系数有关，还与由介质孔隙结构决定的流-固两相动力协调性有关，存在一种动力协调介质，纵波在这种介质中不引起电场.

Numerical simulation and analysis of seismoelectromagnetic wave fields excited by a point source in layered porous media

To understand the characteristics of the electromagnetic (EM) fields during an earthquake, we studied the EM fields induced by the seismic waves in a porous medium due to the electrokinetic effect. Using the Pride′s equations for the coupled poroelastic and electromagnetic fields, we derived the displacement-stress-EM-discontinuity vector for a double couple source, and then calculated the full waveforms generated by such a double couple source. As a comparison, waveforms generated by an explosion source are also simulated. The result shows that a P-wave can induce an accompanying electric field, of which each component has a similar but opposite-phased waveform with the corresponding component of the solid displacement; an S-wave can induce accompanying a magnetic field, which has similar waveform with the solid displacement. The double couple source also generates a kind of radiating EM wave, which propagates independently. Such EM wave is at least one order of magnitude faster than the p-wave, thus arrives at all receivers almost at the same time. However, its amplitude is much weaker than that of the accompanying electric and magnetic fields, and decreases rapidly when offset increases. It is also shown that the amplitude of the accompanying electric field induced by the P-wave not only depends on the amplitude of the P-wave and the electrokinetic coupling coefficient, but also depends on the fluid-solid dynamic compatibility, which is determined by the pore structure. There exists a special kind of porous medium, in which the P-wave cannot induce any accompanying electric field.