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- Title
Numerical Simulation of Electromagnetic Responses to an Earthquake Source Due To the Piezoelectric Effect of '∞m' Symmetry.
- Authors
Zhao, Jie; Gao, Yongxin; Cheng, Qianli; Zhou, Guanqun; Chen, Chieh‐Hung; Zhang, Xuemin; Sun, Yang‐yi
- Abstract
It is reported that earthquakes are accompanied by electromagnetic (EM) anomalies. These anomalies are thought to be caused by earthquakes but their generation mechanism is still unclear. The piezoelectric effect has been proposed as a possible mechanism, particularly in quartz‐rich rocks. However, the EM responses to earthquakes due to such an effect have not been well understood. In this article, we study the EM signals generated by an earthquake source due to the piezoelectric effect. We develop a semi‐analytical method to simulate the EM responses to earthquake sources in a 3‐D layered model and conduct numerical simulations to investigate the characteristics of the EM fields. The results show that the piezoelectric effect in quartz‐rich rocks could be the responsible mechanism for the EM signals recorded during the earthquake. Two kinds of EM signals can be generated by the earthquake, namely, the early EM wave arriving before the seismic waves and the coseismic EM field accompanying the seismic waves. For an Mw 6.1 earthquake, the coseismic electric field is ∼0.1 μV/m and the magnetic field can only reach ∼10−5 nT. We also study the sensitivity of the coseismic EM fields to the rock conductivity. The results indicate that the coseismic EM fields are mainly affected by the conductivity of the shallow layer where the receiver is located, and if the top layer is thin, they are also affected by the conductivity of the deeper layer due to the contribution of the evanescent EM wave created at the interface. Plain Language Summary: When a quartz‐rich rock is under stress, the positive and negative charge centers of quartz crystals are shifted, resulting in a polarization, which manifests macroscopically as the EM radiation. Such a phenomenon is known as the piezoelectric effect. It is a plausible mechanism for the generation of the earthquake‐associated electromagnetic (EM) anomaly. In this paper, we propose a simple method to simulate the EM disturbances generated by an earthquake source arising from the piezoelectric effect. We also conduct numerical simulations to study the properties of the EM fields. The results show that earthquakes can produce two kinds of EM signals. One signal propagates with the speed of the EM wave in the rocks and it arrives earlier than the seismic waves. The other is the coseismic EM field that appears simultaneously with the seismic waves. Such a coseismic signal is restricted to inside of the area disturbed by the seismic wave. Based on the sensitivity analysis, we find that the coseismic EM signal is sensitive not only to the conductivity of shallow rocks, but also to that of the deep rocks. The results also indicate that the electric signals produced by the piezoelectric effect during an earthquake are observable. Key Points: A method is presented to simulate the seismo‐electromagnetic fields due to the piezoelectric effect in quartz‐rich strataAn earthquake source can generate an early electromagnetic (EM) wave and coseismic EM fields due to the piezoelectric effectNumerical results show that the piezoelectric effect is an effective mechanism to produce observable electric signals
- Subjects
PIEZOELECTRICITY; EARTHQUAKES; COMPUTER simulation; EARTHQUAKE zones; QUARTZ crystals; SEISMIC waves; SPACE charge
- Publication
Journal of Geophysical Research. Solid Earth, 2024, Vol 129, Issue 5, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2023JB027756