Abstract
The 2019 M7.1 Ridgecrest earthquake was the strongest one in the last 20 years in California (United States). 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). 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. 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.
Highlights
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 considered as the largest foreshock
Electron Density and Magnetic Field From Satellite For the electron density (Ne), we considered a background based on median values from ionosonde data of hmF2
It is interesting to highlight that our found precursor times are much longer than those identified by many other papers on earthquake precursors, especially ionospheric precursors, which seem to occur only a few hours to days before large earthquakes (e.g., Heki, 2011; He and Heki, 2017; Yan et al, 2017)
Summary
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 considered as the largest foreshock. The analysis of AOT (Figure 6) shows two possible anomalies but only that one around two months before the mainshock looks more reliable: not persistent, it clearly emerges from the overall background In this case, the historical time series starts in 1980, because no data are available before this year. We show plots of dX/dt, dY/dt, and dZ/dt (i.e., the first differences of X, Y, and Z magnetic field components), the logarithm of the electron density Ne along with a green dashed line that is the Ne background level expected from the ionosonde, and the geographic map of the region, where the central star represents the earthquake epicenter, the yellow oval is the Dobrovolsky region, and the south-north red line indicated the satellite track projection at the Earth’s surface. It is interesting to note that in the last period (around one month) approaching the earthquake, the residuals of the magnetic field intensity present more anomalies (highlighted by large red ovals in the figure)
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