Seismoelectric waves generated by a point source in horizontally stratified vertical transversely isotropic porous media

摘要

We study seismoelectric waves due to the electrokinetic ef-fect in vertical transversely isotropic (VTI) media. An analyti-cal method is presented for solving 3D seismoelectric waves generated by a point source and numerical simulations are con-ducted to investigate the characteristics of the seismoelectric waves. The results indicate that three types of seismoelectric signals can be observed, namely, a direct electromagnetic (EM) wave radiated by a seismic source, coseismic electric/ magnetic fields accompanying seismic waves (including qP, qSV, and SH waves), and an EM wave converted at an interface from a seismic wave (i.e., the interface seismoelectric re-sponse). The seismoelectric signals in a VTI medium have some specific properties different from those in an isotropic medium. For example, a qP wave has a coseismic magnetic response, whereas in an isotropic medium a P wave cannot generate any coseismic magnetic field. All the qP, qSV, and SH waves have a direction dependent or anisotropic ability to generate coseismic electric and magnetic fields. The qP wave has the strongest ability to generate the electric field, 1-3 orders stronger than the qSV and SH waves. The qSV and SH waves have a comparable ability to generate the mag-netic field, one order stronger than the qP wave. The results also indicate that the anisotropy in velocity, permeability, and conductivity has great impacts on the interface response. Simulations of an earthquake source demonstrate that the coseismic electric fields are dominated by the qP, qSV, and Rayleigh waves, whereas the coseismic magnetic fields are dominated by the SH and Love waves.