Electromagnetic Fields Generated by an Earthquake Due to the Piezomagnetic Effect

Abstract 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, which is 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 time‐space‐domain seismic and EM responses are obtained through the Hankel transform and inverse Fourier transform. We conduct numerical simulations to investigate the 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 with an epicentral distance of 85 km 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 coseismic EM signals observed in an actual earthquake and find that the piezomagnetic effect possibly contribute to the observed data.