Three‐dimensional distribution of ionospheric anomalies prior to three large earthquakes in Chile

Abstract

Using regional Global Positioning System (GPS) networks, we studied three‐dimensional spatial structure of ionospheric total electron content (TEC) anomalies preceding three recent large earthquakes in Chile, South America, i.e., the 2010 Maule (Mw 8.8), the 2014 Iquique (Mw 8.2), and the 2015 Illapel (Mw 8.3) earthquakes. Both positive and negative TEC anomalies, with areal extent dependent on the earthquake magnitudes, appeared simultaneously 20–40 min before the earthquakes. For the two midlatitude earthquakes (2010 Maule and 2015 Illapel), positive anomalies occurred to the north of the epicenters at altitudes 150–250 km. The negative anomalies occurred farther to the north at higher altitudes 200–500 km. This lets the epicenter, the positive and negative anomalies align parallel with the local geomagnetic field, which is a typical structure of ionospheric anomalies occurring in response to positive surface electric charges.

Ionospheric anomalies immediately before Mw7.0–8.0 earthquakes

“…Obviously, the postseismic hole cannot explain simultaneous starts of artificial preseismic anomalies of both polarities. He and Heki [2016] also pointed out that the three-dimensional structure of the positive and the negative anomalies along the geomagnetic field is consistent with the ionospheric response to positive electric charges on the ground .…”

“…In this paper, we take the height of the layer at the maximum ionization height (~300 km) when we convert STEC to VTEC by multiplying with the cosine of the incident angle of LOS with this thin layer. However, we assume the height at 200 km to draw SIP tracks on the map considering the approximate heights of positive anomalies inferred by He and Heki []. We estimate the accuracy of VTEC derived in the present study as ~0.02 TECU [ Coster et al , ].…”

“…This causes downward E x B drift of ionospheric electrons and redistribution of ionospheric electrons. He and Heki [2016] reported that the three-dimensional structure of positive and negative electron density anomalies before the 2015 Illapel earthquake is consistent with Kuo et al [2014]. Recently, Prokhorov and Zolotov [2017] pointed out a problem in their numerical treatments of the atmospheric electric currents, and Kuo and Lee [2017], in their reply, showed that the problem does not emerge.…”

“…Second, Heki and Enomoto [2015] found that earthquakes with larger M w tend to have longer precursor times (i.e., tend to start earlier). Third, He and Heki [2016] showed that the anomalies of larger earthquakes have larger spatial dimensions. Heki and Enomoto [2015] studied earthquakes with M w ≥ 8.0 (precursors emerged only before earthquakes with M w ≥ 8.2).…”

South Atlantic Anomaly, Ionospheric Signals from Seismic Events

“…These large events have puzzled scientists with pre-seismic signs, which are supposed to forecast the events before they happen. Although some scholars have found electromagnetic signs created from rocks [6][7][8], claiming that they will be detected at the ionosphere [9][10][11], it is still not clear about the propagation mechanism between the Earth's ground and the ionosphere [12,13].…”