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

[MIS09-11] Ionospheric electromagnetic anomalies before the 2021 Madoi Ms7.4 earthquake and their possible coupling mechanism

*Baiyi Yang¹、KaiGuang Zhu¹、Ting Wang¹、Donghua Zhang¹、Wenqi Chen¹、Mengxuan Fan¹、Yiqun Zhang¹、Pu Wang¹、Yuqi Cheng¹ (1.JiLin University)

キーワード：Seismic ionospheric effect, Seismic electromagnetic anomalies, Random matrix theory, Lithosphere-Atmosphere-Ionosphere Coupling mechanism

Electromagnetic anomalies before earthquakes exhibit significant short-term characteristics. This study analyzes the ionospheric effects of the 2021 M7.4 Madoi earthquake in China. Ionospheric anomalies, including electric field, magnetic field, and electron density variations observed by the China Seismo-Electromagnetic Satellite (CSES) and Swarm Satellites in the earthquake region, were extracted using the Non-negative Matrix Factorization (NMF) method. To remove the ionospheric random anomalies, we propose a random matrix theory (RMT) anomaly distinction approach, which involves comparing the eigenvalue distribution of the signal correlation matrix with that of a random matrix to obtain more reliable ionospheric anomalies. Then, the temporal and spatial characteristics of ionospheric anomalies were analyzed. Temporally, the anomalies exhibited sigmoidal growth from -65 to -25 days and followed power-law growth from -20 days until the earthquake. Spatially, the anomalies exhibited a concentration pattern, migrating from the periphery of the study region toward the epicenter. Furthermore, an analysis of the waveform and spectral correlation characteristics of the ionospheric anomalies revealed that these features correspond to phase variations in subsurface stress. Finally, the ionospheric anomalies were compared with previous studies on multi-layer anomalies before the Madoi earthquake. We found three distinct phases, in the early phase, anomaly propagation through the lithosphere, atmosphere, and ionosphere followed an asynchronous chain process. In contrast, in the middle phase, anomalies appeared synchronously across multi-layer. In the impending earthquake phase, the anomalies were directly coupled from the lithosphere to the ionosphere. Therefore, we hypothesize to be a new mechanism related to the dramatic decrease in earth resistivity. These findings highlight the significance of spatiotemporal, waveform, and spectral correlation characteristics in understanding the coupling mechanisms of electromagnetic anomaly propagation across multiple layers.