Coseismic piezoelectric effects due to a dislocation: 1. An analytic far and early-time field solution in a homogeneous whole space

Abstract Piezoelectricity is a property that arises from the crystal anisotropy of substances. Piezoelectric substances generate electromagnetic (EM) field variations related to the temporal variations of the stress field. Since piezoelectric substances are abundant in the earth’s crust, the presence of a coseismic piezoelectric EM phenomenon in the real earth is a reasonable expectation. This paper examines the fundamental characteristics and detectability of coseismic EM signals relating to the piezoelectricity of crustal substances. Combining the fundamental equations of EM fields and the motion of an elastic medium, we derived analytical expressions of EM fields related to the variation of the stress field caused by slip of a point dislocation in a uniform whole space filled with an elastic, conductive, and piezoelectric substance. Numerical calculations, with physical parameters permissible for crustal rocks and a unit step function substituted as the source time function, show that the initial phase of EM signals, amounting to 1 nT and 10 2  mV/km, are observable at a 10 km distance from the slip about 0.01 s after slip occurs, when the seismic moment magnitude is around 7–8. This result suggests difficulty in detecting such piezoelectric EM signals related to earthquakes. However, it is shown that if the observations are succeeded due to a dense observation network installed around the epicenter, information on piezoelectric property relating to the direction of the symmetry axis in the deep seismogeneic zone can be obtained.