Analysis of Seismo-ionospheric Anomaly Disturbance Associ-ated with the Mw7.6 Mexico Earthquake on 19 September 2022

Based on GNSS ionospheric data, this paper detected and investigated the pre-earthquake ionospheric anomalies of the 7.6 magnitude earthquake that occurred in Mexico on September 19, 2022. 10.7 cm solar radio flux (F10.7), sunspot number (SSN), global geomagnetic activity Index (KP) and geomagnetic activity index in equatorial region (DST) are employed to reflect solar and geomagnetic activities, respectively. The result of the sliding quartile range method indicates that the TEC anomaly over the epicenter on 15th day before the earthquake was the most significant, but the geomagnetic activity was abnormal on that day. To further distinguish whether the ionospheric disturbance on 15th day was caused by geomagnetic activity or earthquake, this paper adopts the coherent wavelet to analyze the time-varying relationship between total electron content (TEC) and geomagnetic activity in the time-frequency space. The results show that the correlation between TEC, Kp and Dst is slightly weakened in the low-frequency range due to the enhancement of geomagnetic activity on 15th day, but the phase relationship remained stable. While the strong correlation between TEC, Kp and Dst suddenly disappeared and phase relationship sharply changed after 10th day. This was due to the influence of seismic-ionospheric coupling effect, where the abnormal disturbances in TEC disrupted the pre-existing stable relationship between TEC, Kp, and Dst. Therefore, we conclude that the TEC anomaly on 10th day before the earthquake was the precursor to the Mw7.6 Mexico.