Detecting Seismo-Ionospheric Anomalies Possibly Associated With The 2019 Ridgecrest (California) Earthquakes By Gnss, Cses, And Swarm Observations

The association between earthquakes and ionospheric precursors has been widely reported in previous studies. The Swarm satellite constellation, the China Seismo-Electromagnetic Satellite (CSES), and the ground-based global navigation satellite system (GNSS) observations provide us new opportunities to detect ionospheric precursors to earthquakes for a better understanding of the seismic-ionospheric coupling. In California, two shallow earthquakes with magnitudes of 6.5 and 7.1, the two higher magnitude events of the Ridgecrest earthquakes sequence, occurred on July 4 and July 6, 2019, respectively. This study adopted total electron content (TEC) data from the GNSS, and electron density (N-e), and electron temperature (T-e) data from the CSES and Swarm to study the possible ionospheric perturbations before the Ridgecrest earthquakes. A sliding interquartile range method was used to analyze the TEC data, and a spatial differential method and a revisit trajectory comparison were used to analyze the N-e and T-e data. While excluding the influences of various factors including solar and geomagnetic activities, planetary waves, tropospheric convection, and medium-scale traveling ionospheric disturbances, the cross-validation of the multi-source data found that anomalies detected on June 20, June 22, and June 26-29, 2019 could be regarded as precursors of the Ridgecrest earthquakes. A spatial distribution analysis showed that the pre-earthquake anomalies offset the equatorial direction. TEC anomalies were all positively correlated with the N-e anomalies, with most of them were positive. The N-e and T-e anomalies were both positively and negatively correlated with mostly negative, while showing a strong linear negative correlation at nighttime.