4:30 PM - 4:45 PM
[SEM16-11] Revision of governing equations describing the seismo-electromagnetic coupling in porous media and some of its consequences
Keywords:seismo-electromagnetic coupling, porous media, geomagnetic field
The electrokinetic effect and the motional induction effect are the dominant mechanisms through which the vibration of the porous media is coupled with temporal variations in the electromagnetic field. Two couplings have described by independent set of equations so far; however, they should be described in a single set of equations in principle. The presenter re-considered the derivation of the conventional set of equations to derive a modified set of equations that simultaneously describe both effects, and analyzed them to assess whether the unknown types of phenomena should exist.
Conventional set of equations that describes coupling between the seismic and electromagnetic wavefields in a porous medium via the electrokinetic effect should be revised in such a way that the effect of ambient magnetic field (i.e. the geomagnetic field) is incorporated. The revision of equation is accomplished by replacing E in transport equations by E+vxB, where E, v, and B are the electric field, the ground velocity and the ambient (geomagnetic) magnetic field. The revised set of equations describes wavefields related to the electrokinetic and motional induction effects in a unified fashion, which has been described in separate sets of equations so far.
For a case of plane waves in a uniform medium, the seismo-EM waves are categized into three modes according to the combination of directions of wave propagation, polarity of seismic wave, and the ambient magnetic field. Only in one mode, a "resonance" due to the coupling of the electrokinetic and the motional induction effects is predicted which has not been predicted by conventional set of equations. However, the required time for the resonance to generate the electromagnetic field large enough to be observed is far larger than the persistent time of the seismic waves. In practice, therefore, there will be no difference between solving the revised set of equations and solving the conventional two set of equations for electrokinetic and motional induction effects separately.
Conventional set of equations that describes coupling between the seismic and electromagnetic wavefields in a porous medium via the electrokinetic effect should be revised in such a way that the effect of ambient magnetic field (i.e. the geomagnetic field) is incorporated. The revision of equation is accomplished by replacing E in transport equations by E+vxB, where E, v, and B are the electric field, the ground velocity and the ambient (geomagnetic) magnetic field. The revised set of equations describes wavefields related to the electrokinetic and motional induction effects in a unified fashion, which has been described in separate sets of equations so far.
For a case of plane waves in a uniform medium, the seismo-EM waves are categized into three modes according to the combination of directions of wave propagation, polarity of seismic wave, and the ambient magnetic field. Only in one mode, a "resonance" due to the coupling of the electrokinetic and the motional induction effects is predicted which has not been predicted by conventional set of equations. However, the required time for the resonance to generate the electromagnetic field large enough to be observed is far larger than the persistent time of the seismic waves. In practice, therefore, there will be no difference between solving the revised set of equations and solving the conventional two set of equations for electrokinetic and motional induction effects separately.