Enhancement of co-seismic piezomagnetic signals near the edges of magnetization anomalies in the Earth’s crust

Abstract

A scheme is proposed for calculating the piezomagnetic fields that accompany the propagation of seismic waves through a non-uniformly magnetized crust. Examples of the calculations are provided. Generally, the calculation of the co-seismic piezomagnetic fields involves laborious three-dimensional volume integrals, even if the magnetization structure is two-dimensional. However, the calculation can be simplified by taking the Fourier transform of spatial distributions of the field into consideration. As an example, we have performed calculations for both the non-uniformly and uniformly magnetized crust with an intensity of 10 A/m. The incident seismic wave is considered to consist of Rayleigh waves with an amplitude of 5 cm. The amplitudes of the piezomagnetic signals arising from uniformly magnetized crust are up to 0.2 nT, whereas those arising from non-uniformly magnetized crust are as large as 0.5 nT. This result indicates that the piezomagnetic field may be a plausible mechanism of generating co-seismic changes in the magnetic field with detectable amplitudes for large earthquakes, provided that the observation site is located near the magnetization boundaries.