[M-IS09] Interdisciplinary studies on pre-earthquake processes

[MIS09-13] Time-varying electromagnetic responses to an earthquake source due to the piezomagnetic Effect

*Yongxin Gao¹ (1.Hefei University of Technology)

キーワード：earthquake, electromagnetic field, piezomagnetic effect, semi-analytical numerical modeling

Stress change in ferromagnetic-minerals-bearing rocks can change the rock magnetization and lead to the variation in magnetic field, known as the piezomagnetic effect and proposed to be a possible mechanism for the earthquake-associated electromagnetic (EM) signals. Previous studies are mostly based on elastostatics to obtain a static piezomagnetic field generated by a dislocation or pressure source, which is not sufficient to explain the observed time-varying EM signals during an earthquake. In this study, we investigate the time-varying EM response generated by an earthquake due to the piezomagnetic effect. We propose an analytically-based method to simulate the seismic and EM fields in a horizontally layered model, in which the coupled elastodynamic and Maxwell’s equations are solved in the frequency-wavenumber domain. The seismic and EM responses in the time-space domain are then obtained through the Hankel transform and inverse Fourier transform. We conduct numerical simulations to investigate properties of the EM responses to earthquakes. The results show that variations in not only magnetic fields but also electric fields can be generated due to the piezomagnetic effect. For an M_w 6.0 earthquake, a receiver located 85 km from the epicenter can receive coseismic electric and magnetic fields of ~0.1 μV/m and ~0.1 nT, which are detectable by current EM equipment, demonstrating that the piezomagnetic field is an effective mechanism for the generation of earthquake-associated EM disturbances. We apply the method to simulating the observed coseismic EM signals in an actual earthquake and find that the predicted magnetic fields explain well the observed data.