Analysis of Seismo-Ionospheric Anomaly Disturbance Associated with the Mw7.6 Mexico Earthquake on 19 September 2022

GNSS ionospheric records are valuable measurements of earthquake-related ionospheric anomalies. The deep exploration of GNSS ionospheric data can help to better understand the seismic–ionospheric coupling effect. Thus, we used GNSS ionospheric data to detect and investigate the pre-earthquake ionospheric anomalies of the 7.6 magnitude earthquake, which occurred in Mexico on 19 September 2022. A 10.7 cm solar radio flux (F10.7), sunspot number (SSN), and geomagnetic activity indices (Dst and Hp30) are employed to reflect solar and geomagnetic activities, respectively. The result of the sliding quartile range method indicates that there was a ionospheric disturbance over the epicenter on the 10th day prior to the earthquake, and that there were no anomalies observed in solar activity and geomagnetic activity on that day. Meanwhile, the ionospheric 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 the 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 and phase relationship between TEC, Dst, and Hp30 remained relatively stable on the 15th day before the earthquake, while the strong correlation between TEC, Dst, and Hp30 suddenly disappeared and the phase relationship sharply changed after the 10th day. This may be due to the influence of the seismic–ionospheric coupling effect, where the abnormal disturbances of TEC may disrupt the pre-existing stable relationship between TEC, Dst, and Hp30. Therefore, we conclude that the TEC anomaly on 10th day before the earthquake might be the precursor to the Mw7.6 Mexico earthquake.