Finite Element Simulation Of Seismoelectromagnetic Coupling Wave Field

Earthquake-induced electromagnetic phenomenon is a frontier issue of great concern in the field of geoscience at home and abroad.Many data shown that when an earthquake occurs,it will trigger seismic wave,and induce electromagnetic wave signal where the seismic wave passes by,which is also known as the seismoelectric coupling phenomenon.The essence of seismoelectric coupling is the coupling between mechanical energy and electromagnetic energy.This phenomenon has attracted much attention.Its internal mechanism and trigger mechanism are still unclear.The electric double layer electrokinetic effect is one of the most likely mechanisms to explain the seismoelectric coupling at present.In this paper,based on the galvanic effect of the electric double layer,the excitation and propagation characteristics of the seismic wave field in the horizontal and undulating surface and irregular interface are studied,as well as the pre-earthquake electromagnetic anomaly response induced by the seepage of underground fluid.The predecessors' understanding of the coupling of seismic waves and electromagnetic fields is mainly based on a regular model.In order to study the excitation and propagation characteristics of seismic wave fields in strata with undulating surface and underground interfaces,this paper uses the finite element software COMSOL Multiphysics to simulate point source excitation Electromagnetic field.The two-dimensional SHTE and PSVTM mode seismoelectric coupling equations in the frequency domain are given respectively,then the calculation model is established using COMSOL software,and the frequency domain response of the seismic wave field excited by the point force source is solved.Finally,the seismic wave field and electromagnetic field are obtained by FFT transform Time domain waveform.The simulation results show that there are three types of electromagnetic signals in the seismic wave field.The first type is the electromagnetic wave directly excited by the source;the second type is the electromagnetic wave excited by the seismic wave at the interface(including the free surface and the interface between different underground media);The third type is the coseismic signal accompanied by the seismic wave.The first two electromagnetic waves arrive at the distant observation station earlier than the seismic wave,which is of great significance for earthquake early warning.In addition,the study also found that when the seismic wave propagates to the surface and along the surface,an electromagnetic disturbance signal accompanying the seismic wave propagation is also recorded in the air layer near the surface.Under the condition of the same horizontal source distance,the signal is received by the underground observation point.The electromagnetic signal is the same,which is consistent with some previous observations.The results of this paper provide theoretical evidence for the interpretation of seismic electromagnetic signals in the future.Electromagnetic anomaly signals before earthquakes are often regarded as a possible precursor signal,and the fluid in the pores of underground rocks plays an important role in the process of earthquake inoculation and occurrence.In this paper,the same finite element software is used to carry out numerical simulation work.First,a 2D finite element model is established.The equation used is the coupling of the fluid diffusion equation and the Maxwell equations.Then,the transient solver is used to solve it.Finally,the induced fluid infiltration process is obtained.Electromagnetic signals.The results show that the electromagnetic wave signal can be excited at the boundary of different pressure areas by fluid seepage.The characteristics of the signal are that the electromagnetic signal observed at the receiving point reaches the peak value in a very short time,then gradually weakens with the seepage process signal,finally decays to 0,and responds in both electric and magnetic fields.