Abstract
Many studies have reported that there is a coupling mechanism between ionosphere and earthquake (EQ). Ionospheric anomalies in the form of abnormal increases and decreases of ionospheric Total Electron Content (TEC) are even regarded as precursors to EQs. In this paper, TEC anomalies associated with three major EQs were investigated by Global Ionospheric Maps (GIMs) and GPS-TEC, including Kumamoto-shi, Japan—EQ occurred on 15 April 2016 with Mw = 7.0; Jinghe, China—EQ occurred on 8 August 2017 with Mw = 6.3; and Lagunas, Peru—EQ occurred on 26 May 2019 with Mw = 8.0. It was found that the negative ionospheric anomalies linger above or near the epicenter for 4–10 h on the day of the EQ. For each EQ, the 10-min sampling interval of TEC was extracted from three permanent GPS stations around the epicenter within 10 days before and after the EQ. Variations of TEC manifest that the negative ionospheric anomalies first appear 10 days before the EQ. From 5 days before to 2 days after the main shock, the negative ionospheric anomalies were more prominent than the other days, with the amplitude of negative ionospheric anomaly reaching −3 TECu and the relative ionospheric anomaly exceeding 20%. In case of Kumamoto-shi EQ, the solar-geomagnetic conditions were not quiet (Dst < −30 nT, Kp > 4, and F10.7 > 100 SFU) on the suspected EQ days. We discussed the differences between ionospheric anomalies caused by active solar-geomagnetic conditions and EQ. Combining the analysis results of Jinghe EQ and Lagunas EQ, under quiet solar-geomagnetic conditions (Dst > −30 nT, Kp < 4, and F10.7 < 100 SFU), it can be found that TEC responds to various solar-geomagnetic conditions and EQ differently. The negative ionospheric anomalies could be considered as significant signals of upcoming EQs. These anomalies under different solar-geomagnetic conditions may be effective to link the lithosphere and ionosphere in severe seismic zones to detect EQ precursors before future EQs.
Highlights
Many studies have reported that there is a coupling mechanism between ionosphere and earthquake (EQ)
The ionospheric anomalies associated with three Mw > 6.0 EQs were detected by Global Ionospheric Maps (GIMs) and Global Positioning System (GPS)-Total Electron Content (TEC)
When establishing the ionospheric anomaly detection method, it is important to confirm whether the method produces incorrect detection under normal conditions and if the method fails to produce a correct detection under abnormal conditions
Summary
Many studies have reported that there is a coupling mechanism between ionosphere and earthquake (EQ). The negative ionospheric anomalies could be considered as significant signals of upcoming EQs. The negative ionospheric anomalies could be considered as significant signals of upcoming EQs These anomalies under different solar-geomagnetic conditions may be effective to link the lithosphere and ionosphere in severe seismic zones to detect EQ precursors before future EQs. Since the study of Leonard and Barnes [1] discovered that there is a potential coupling mechanism between earthquake (EQ) and abnormal ionospheric disturbance from the Alaska EQ in 1964, several researches have been devoted to detect short- and long-term seismo-ionospheric anomalies from ionospheric remote sensing measures. During the 27-day period before the EQ, negative and positive anomalies appeared in the ionosphere, which were not related to active solar-geomagnetic conditions [9]. Thomas et al [16]
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