Numerical simulations to explain the coseismic electromagnetic signals: a case study for a M5.4 aftershock of the 2016 Kumamoto earthquake

Abstract

Coseismic electromagnetic (EM) signals that appear from the P arrival were observed in a volcanic area during the 2016 Kumamoto earthquake. In this study, we conduct numerical simulations to explain the coseismic EM signals observed for a M5.4 aftershock of the earthquake. Initially, we adopt a water-saturated half-space model, and its simulation result for a receiver with a depth of 0.1 m suggests that the magnetic signals do not show up at the arrivals of P, refracted SV-P and Rayleigh waves because the evanescent EM waves just counterbalance the localized magnetic signals that accompany P, refracted SV-P and Rayleigh waves. Then, we conduct numerical simulations on a sevenlayer half-space model in which the second layer corresponds to an aquifer analogy and the six other layers refer to air-saturated porous media. When only the electrokinetic effect is considered, the simulated coseismic magnetic signals still appear from the S arrival. The combination of electrokinetic effect and surface-charge assumption is also tested. We find that signals before the S arrival are missing on the transverse seismic, transverse electric, radial magnetic and vertical magnetic components, although the situation on horizontal magnetic components is improved to an extent. Then, we introduce an artificial scattering effect into our numerical simulations given that the scattering effect should exist in the volcanic area. New numerical result shows good agreement with the observation result on the signal appearance time. Hence, the combination of electrokinetic and scattering effects is a plausible explanation of coseismic EM signals. Further investigations indicate that coseismic electric and/or magnetic signals are more sensitive to the scattering effect and the aquifer thickness than seismic signals.

Electromagnetic Field Generated by an Earthquake Source Due to Motional Induction in 3D Stratified Media, and Application to 2008 Mw 6.1 Qingchuan Earthquake

“…Both theoretical and experimental studies have confirmed that the EK effect couples the seismic and EM fields (e.g., Garambois & Dietrich, 2002;Haartsen & Pride, 1997;Zhu et al, 1999). EK modeling techniques predict that an earthquake source can generate two kinds of EM signals, namely, the early and coseismic EM signals, and when applied to real earthquake events they can explain much of the observed data (Gao et al, 2016(Gao et al, , 2020Ren et al, 2014;Sun et al, 2019). For example, Gao et al (2016) simulated the coseismic EM data observed during the 2004 Parkfield M6 earthquake using a finite-fault model by the method of Hu and Gao (2011) and found that the simulated coseismic electric field matched the observed data in both amplitude and waveforms, showing the EK effect may explain the coseismic EM phenomenon.…”

“…The EM signals measured during passage of seismic waves (hereafter referred to as coseismic EM signals) tend to be very similar to the corresponding seismic signals in waveform and frequency content (Gao et al., 2016; Matsushima et al., 2002; Sun et al., 2019; Tang et al., 2010). They may carry useful information about the subsurface material properties (Gao et al., 2016; Huang et al., 2015; Ren et al., 2016).…”

“…Both theoretical and experimental studies have confirmed that the EK effect couples the seismic and EM fields (e.g., Garambois & Dietrich, 2002; Haartsen & Pride, 1997; Zhu et al., 1999). EK modeling techniques predict that an earthquake source can generate two kinds of EM signals, namely, the early and coseismic EM signals, and when applied to real earthquake events they can explain much of the observed data (Gao et al., 2016, 2020; Ren et al., 2014; Sun et al., 2019). For example, Gao et al.…”

“…It has been widely reported that electromagnetic (EM) disturbances are detected before and during the arrival of seismic waves from earthquakes, especially large earthquakes (Abdul‐Azeez et al., 2009; Chen et al., 2019; Gao et al., 2016, 2019; Gershenzon et al., 1993; Honkura et al., 2000; Iyemori et al., 1996; Johnston & Mueller, 1987; Karakelian et al., 2002; Okubo et al., 2011; Rikitake, 1968; Sun et al., 2019; Tang et al., 2010; etc.). This is an interesting and important phenomenon because of its potential application to earthquake early warning and disaster mitigation.…”

Refining Higher Modes of Rayleigh Waves Using Seismoelectric Signals Excited by a Weight‐Drop Source: Study From Numerical Simulation Aspect

“…Based on numerical simulations, Ren et al (2016b) put forward the idea that evanescent seismoelectric waves could be the main contribution to coseismic EM signals. This idea was recently adopted to investigate actual coseismic EM signals associated with natural earthquakes (Dzieran et al, 2019;Sun et al, 2019).…”