Electromagnetic signals related to incidence of a teleseismic body wave into a subsurface piezoelectric body

Abstract

This paper presents a case study of Electromagnetic (EM) signals associated with earthquakes due to the piezoelectricity of crustal rocks. For a simple model of crustal structure with a subsurface piezoelectric body, a mathematical expression was obtained that describes the behavior of piezoelectric EM signals due to incidence of a teleseismic body wave. Using this expression, we evaluated expected EM signals with physical parameters reasonable for crustal rocks. Results of the frequency domain analysis suggested that the intensity of the signal decreases with decreasing frequency due to decreasing stress rate at lower frequencies, and decreases with increasing frequency due to EM attenuation in the conducting medium at higher frequencies. However, the latter (the skin effect) was shown to be negligible at the dominant frequency range of seismic waves so far as a shallower piezoelectric body is concerned. Numerical results also indicated a resonant feature of the piezoelectric EM signals corresponding to geometry of the subsurface piezoelectric body. However, numerical calculations suggested that such signals cannot be detected except for strong motions. If detected, on the other hand, their spatial and frequency characteristics will provide information on the geometry of the subsurface piezoelectric body.