Nevertheless, it is rather difficult to think that a so large energetic phenomenon such as a strong earthquake cannot provide any sign of its preparation (e.g., Sobolev et al., 2002 Bulut 2015). We know how much difficult the study of what happens before a large earthquake is and how controversial the concept of preparation phase of an earthquake is within the scientific community. Recent works on the Ridgecrest seismic sequence revealed much of the complexity of the seismic source of the major ruptures and relative mechanisms (e.g., Barnhart et al., 2019 Ross et al., 2019 Chen et al., 2020), but nothing was investigated about the preparation phase of the seismic sequence and its possible coupling with the above geolayers, such as the atmosphere and ionosphere. After 21 days, they were followed by more than 111,000 aftershocks (M > 0.5, Ross et al., 2019), mainly within the area of the Naval Air Weapons Station China Lake (California). These major shocks occurred north and northeast of the town of Ridgecrest, California (about 200 km north-northeast of Los Angeles). This earthquake was the most powerful event occurring in California in the last 20 years (after the M7.1 1999 Hector Mine earthquake, e.g., Rymer et al., 2002). The sequence of foreshocks continued with numerous events with magnitude from intermediate to large (e.g., an M5.4 about 16 h, and an M5.0 almost 3 min before the mainshock) culminating with the M7.1, which struck on 6 July at 03:19 UTC. The 2019 Ridgecrest seismic sequence started on July 4, 2019: many small magnitude events (Ml ∼ 0) preceded by 2 h the major earthquake with a 6.4 magnitude ( Ross et al., 2019), occurred at 17:33 UTC on 4 July and now considered as the largest foreshock. The results are encouraging showing a chain of processes that connect the different geolayers before the earthquake, with the cumulative number of foreshocks and of all other (atmospheric and ionospheric) anomalies both accelerating in the same way as the mainshock is approaching. We analyzed the data in order to identify possible anomalies that cannot be explained by the typical physics of each domain of study and can be likely attributed to the lithosphere-atmosphere-ionosphere coupling (LAIC), due to the preparation phase of the Ridgecrest earthquake.
In a multiparametric fashion, we collected data from the lithosphere (seismicity), atmosphere (temperature, water vapor, aerosol, and methane), and ionosphere (ionospheric parameters from ionosonde, electron density, and magnetic field data from satellites). The 2019 M7.1 Ridgecrest earthquake was the strongest one in the last 20 years in California (United States). 2School of Remote Sensing and Geomatics Engineering, Nanjing University of Information Science and Technology, Nanjing, China.1Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy.Angelo De Santis 1*, Gianfranco Cianchini 1, Dedalo Marchetti 1,2, Alessandro Piscini 1, Dario Sabbagh 1, Loredana Perrone 1, Saioa Arquero Campuzano 1 † and Sedat Inan 1 †
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