Ionospheric Anomalies before the 2015 Deep Earthquake Doublet, Mw 7.5 and Mw 7.6, in Peru

Abstract

Two major earthquakes separated by ∼5 minutes occurred in the same fault in Peru at depths of 606.2 and 620.6 km on November 24, 2015. By using Global Ionospheric Maps (GIMs) from the Center for Orbit Determination in Europe (CODE) and a broadly used statistical method, differential Vertical Total Electron Content (VTEC) maps were derived. Two positive ionospheric anomalies were clearly identified in the differential VTEC maps 2 and 1 day prior to the day of the earthquakes. These anomalies were located inside the earthquakes' preparation regions defined by the Dobrovolsky equation. On the other hand, due to the low-latitude nature of the seismic events, the Equatorial Ionization Anomaly (EIA) shape was also analyzed. A third positive disturbance was revealed between November 20 and 21, 2015. For the aforementioned anomaly and the one on November 22 (2 days before the earthquakes), an enhancement of the VTEC was observe through the considerable modification of the EIA shape into a well-defined double-crest with a trough. By looking into the Dst and Kp indices, the geomagnetic conditions starting on November 20 until the 24 were very quiet; thus, it is considered that the three detected anomalies are precursors to the earthquake doublet. Moreover, it is suggested that the mechanism at work that produced the positive disturbances is the air ionization through the release of radon from the Earth's crust.

Co-Seismic Magnetic Field Perturbations Detected by Swarm Three-Satellite Constellation

“…From the catalogue, all recorded events from 25 November 2013 to 12 April 2019 with a magnitude equal to or greater than 5.5 were downloaded and represented with a black star or dot in Figure 1 according to their geographical distribution (Figure 1a) and the magnitude/depth distribution (Figure 1b). Although some authors also included deep earthquakes in ionospheric disturbance investigations [15,16], we prefer to exclude them, as we consider the possibility that deep earthquakes could affect the ionosphere to be lower. To achieve this selection, all Mw5.5+ events up to 20 km depth were selected and for more in-depth events, a selection based on a higher magnitude and depth was applied.…”