A comprehensive study of geomagnetic and TEC disturbances in relation to M ⩾ 5.0 earthquakes

Previous studies have demonstrated the interaction between multiple layers of the Earth and seismic activity, specifically the lithosphere - atmosphere – ionosphere (LAI) coupling, which is the focus of the present study. Anomalies in LAI parameters, such as variations in geomagnetic field and total electron content (TEC) before seismic activity, have been regarded as earthquake precursors by previous researchers. However, earlier studies used only single parameters and had a limited number of case studies. This study aimed to investigate pre-earthquake anomalies using a dual-parameter approach. Geomagnetic field and TEC variations were used to investigate the relationship between the Earth's layers and earthquakes. Utilising global geomagnetic data and TEC data, a comprehensive analysis was conducted on the variations of geomagnetic and TEC data for the 60 days preceding and five (5) days following the occurrences of the 694 earthquakes with magnitudes greater than and equal to 5.0 (M ⩾ 5.0) in the Japan region in 2011. Following the exclusion of days with geomagnetic storms, referred to as disturbed days, this investigation focused solely on undisturbed days. This study explored and compared geomagnetic and ionospheric disturbances during these undisturbed days preceding the earthquakes. Both geomagnetic and TEC precursors were significantly found in moderate and shallow earthquakes. It was revealed that, preceding the studied earthquake events, anomalous behaviours were evident in both geomagnetic and TEC variations, and these behaviours persisted even on undisturbed days. The study also observed that anomalous TEC parameters occurred within the same time frame as the geomagnetic anomalies, and they were found to be detected a month before the earthquakes. The occurrence rate of the geomagnetic precursors was higher of 65 %, than that of the TEC precursors of 11 %. These observations suggest that the preparation process for earthquakes could impact the ground and upper atmosphere, as described by the LAI coupling mechanism.

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