Abstract
Due to the complex processes of earthquake preparation, the observations and studies associated with earthquakes have attracted the attention of geophysicists for many years. The CSES was successfully launched on 2 February 2018. This satellite can provide global data of the electromagnetic field, plasma, and energetic particles in the ionosphere to monitor and study the ionospheric perturbations associated with earthquakes. Focusing on the characteristics of CSES, a spatial analysis method was proposed to extract the disturbances of electron density prior to earthquakes. Taking Indonesia Mw6.9 earthquake that occurred on 5 August 2018 as an example, the spatial method was illustrated and verified by another analysis method also using the data of electron density and GPS TEC data with the same analysis method. Based on the electron density of CSES for more than 2 years, this method was applied to carry out the statistical study prior to Mw ≥ 6.0 global earthquakes using the superposed epoch and space approach (SESA) method. It was found that 1) relative to the epicenters, seismo-ionospheric disturbances are more obvious in the equator direction than those in the polar direction; 2) the anomalies within 300 km distance from the epicenter are significant 11, 3, and 2 days prior to Mw ≥ 6.0 earthquakes; 3) the influence region of perturbances associated with earthquakes enlarges with the magnitude increase, and the stronger magnitude is the earlier disturbance appears. These statistical characteristics were not detected for the random earthquakes. Comparing the statistical result with the simulation output, the electric field pathway could be considered as the main channel of lithosphere–atmosphere–ionosphere coupling.
Highlights
The abnormal ionospheric plasma density variations before and/or after earthquakes have attracted much attention from the geophysicists for many years (e.g., Pulinets and Legen’ka, 2003; Pulinets and Boyarchuk, 2004; Le et al, 2015)
Focused on the earthquakes that occurred at Taiwan, Liu et al (2000) found the critical frequency of the F2 layer which fell below the lower threshold 1–6 days prior to Mw ≥ 6.0 earthquakes, and Liu et al (2004a) detected foF2 and total electron content (TEC) both decreased 4 days before M ≥ 5.0 earthquakes
Using the spatial analysis method, relative changes of Ne data observed by China Seismo-Electromagnetic Satellite (CSES) in the daytime and nighttime were analyzed from 21 July to 5 August 2018, which includes 15 days before and the occurrence day of Indonesia Mw6.9 earthquake
Summary
The abnormal ionospheric plasma density variations before and/or after earthquakes have attracted much attention from the geophysicists for many years (e.g., Pulinets and Legen’ka, 2003; Pulinets and Boyarchuk, 2004; Le et al, 2015). Ionospheric measuring techniques are categorized as ground and space observations to obtain the ionospheric parameters (Xiong et al, 1999) The former one includes the ground-based ionosonde, global position system (GPS) or global navigation satellite system (GNSS) receivers, and incoherent scatter radar (Rishbeth and Garriott 1969; Schunk and Nagy 2009). Yan et al (2017) applied the statistics method to analyze the ion density of the DEMETER satellite and found that perturbations occur around 200 km from the epicenters in 5 days before the earthquakes. A statistical study prior to Mw ≥ 6.0 global earthquakes was carried out to investigate the characteristics of seismo-ionospheric anomalies using the CSES Ne data from 1 May 2018 to 30 September 2020. The satellite works in the survey mode with a 3-s sampling rate
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