Abstract
We analyze retrospectively/prospectively the transient variations of six different physical parameters in the atmosphere/ionosphere during the M7.8 and M7.3 earthquakes in Nepal, namely: 1) outgoing longwave radiation (OLR) at the top of the atmosphere (TOA); 2) GPS/TEC; 3) the very-low-frequency (VLF/LF) signals at the receiving stations in Bishkek (Kyrgyzstan) and Varanasi (India); 4) Radon observations; 5) Atmospheric chemical potential from assimilation models; and; 6) Air Temperature from NOAA ground stations. We found that in mid-March 2015, there was a rapid increase in the radiation from the atmosphere observed by satellites. This anomaly was located close to the future M7.8 epicenter and reached a maximum on April 21–22. The GPS/TEC data analysis indicated an increase and variation in electron density, reaching a maximum value during April 22–24. A strong negative TEC anomaly in the crest of EIA (Equatorial Ionospheric Anomaly) occurred on April 21, and a strong positive anomaly was recorded on April 24, 2015. The behavior of VLF-LF waves along NWC-Bishkek and JJY-Varanasi paths has shown abnormal behavior during April 21–23, several days before the first, stronger earthquake. Our continuous satellite OLR analysis revealed this new strong anomaly on May 3, which was why we anticipated another major event in the area. On May 12, 2015, an M7.3 earthquake occurred. Our results show coherence between the appearance of these pre-earthquake transient’s effects in the atmosphere and ionosphere (with a short time-lag, from hours up to a few days) and the occurrence of the 2015 M7.8 and M7.3 events. The spatial characteristics of the pre-earthquake anomalies were associated with a large area but inside the preparation region estimated by Dobrovolsky-Bowman. The pre-earthquake nature of the signals in the atmosphere and ionosphere was revealed by simultaneous analysis of satellite, GPS/TEC, and VLF/LF and suggest that they follow a general temporal-spatial evolution pattern that has been seen in other large earthquakes worldwide.
Highlights
The observational evidence of data from the last 3 decades from different parts of the world provides a significant pattern of transient anomalies preceding earthquakes (Tronin et al, 2002; Liu et al, 2004; Ouzounov et al, 2007; Nĕmec et al, 2008; Parrot, 2009; Kon et al, 2010; Hayakawa et al, 2013; Tramutoli et al, 2013)
The maximum offsets from the mean value reached near +5°C on April 20 and +4°C on May 5 (Figure 2C) with a confidence level of more than +2 sigma for all the observations from 2011 to 2015. This transient rapid increase in the surface air temperature is a little more significant than the remote satellite observations shown in Figure 2A, which agrees with the thermodynamic processes explained by the lithosphere-atmosphereionosphere coupling (LAIC) concept. (Pulinets and Ouzounov, 2011)
The analysis reported in this paper about earthquakes in Nepal in April-May 2015 is based on these data recorded by the Very Low Frequency (VLF)/LF stations in Bishkek (KGZ) and Varanasi (VAR)
Summary
The observational evidence of data from the last 3 decades from different parts of the world provides a significant pattern of transient anomalies preceding earthquakes (Tronin et al, 2002; Liu et al, 2004; Ouzounov et al, 2007; Nĕmec et al, 2008; Parrot, 2009; Kon et al, 2010; Hayakawa et al, 2013; Tramutoli et al, 2013). We focus on the consistent multi-parameter data collection that could help to reveal the connection between atmospheric and ionospheric variations (or anomalies) associated with major earthquakes
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