Existence of Evanescent Electromagnetic Waves Resulting from Seismoelectric Conversion at A Solid–porous Interface

ren, hengxin ; huang, qinghua ; chen, xiaofei;

Adopting a model with two half-spaces that consist of solid and porous materials, we numerically investigate the seismoelectric conversion at the solid–porous interface. First, the wave fieldsinalow-porositytwo-layermodelarecomparedwiththoseinahomogeneousfull-space model. The consistency of seismic waves is a validation of our program. We are interested in the quasi-coseismic electromagnetic (EM) signals recorded in the solid area near the interface because they seemingly accompany seismic waves. Then, further numerical simulations on an ordinary two-layer model are conducted. On the basis of time slice snapshots and theoretical analysis, we determine that quasi-coseismic EM signals are essentially non-coseismic EM fields, which include radiation and evanescent EM waves. Evanescent EM waves are induced by the seismic waves that arrive at the interface with the incident angle greater than the critical angle. These waves decay faster than radiation EM waves when moving away from the interface. In the porous layer, evanescent EM waves can hardly be recognized unless they are separated from coseismic EM signals. This finding can be the reason why evanescent EM waves have not been identified in previous seismoelectric studies. Awareness of the fact that seismoelectric conversion at an interface can generate evanescent and EM waves is likely to result in a comprehensive understanding and improved interpretation of the seismoelectric coupling phenomenon.