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

Piezoelectricity is a property that arises from the crystal anisotropy of s ubstances. Piezoelectric substances generate electromagnetic (EM) field var iations related to the temporal variations of the stress field. Since piezo electric substances are abundant in the earth's crust, the presence of a co seismic piezoelectric EM phenomenon in the real earth is a reasonable expec tation. This paper examines the fundamental characteristics and detectability of co seismic EM signals relating to the piezoelectricity of crustal substances. Combining the fundamental equations of EM fields and the motion of an elast ic medium, we derived analytical expressions of EM fields related to the va riation of the stress field caused by slip of a point dislocation in a unif orm whole space filled with an elastic, conductive, and piezoelectric subst ance. Numerical calculations, with physical parameters permissible for crustal ro cks 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, ar e observable at a 10 km distance from the slip about 0.01 s after slip occu rs, when the seismic moment magnitude is around 7-8. This result suggests d ifficulty in detecting such piezoelectric EM signals related to earthquakes . However, it is shown that if the observations are succeeded due to a dens e observation network installed around the epicenter, information on piezoe lectric property relating to the direction of the symmetry axis in the deep seismogeneic zone can be obtained. (C) 2000 Elsevier Science B.V. All righ ts reserved.