Relation of atmospheric and ionospheric anomalies prior to three large earthquakes in Greece

This investigation aims to identify possible pre-earthquake ionospheric and atmospheric anomalies and observe their possible relationship, by employing various methodologies. Three large earthquakes in Greece are selected (6.9Mw, 6.6Mw and 6.3Mw, during 24 May 2014, 20 July and 12 June 2017 respectively). For this purpose, Total Electron Content (TEC) obtained from Global Navigation Satellite System (GNSS) networks and Atmospheric Chemical Potential (ACP) variations retrieved from atmospheric model are examined with the aid of spectral analysis on TEC measurements and of ACP time series. It is shown that ionospheric anomalies which take place from one to few days prior to the three seismic events are most probably related to the forthcoming events and they are synchronous (in the same day) or they are following ACP anomalies (up to 5 days later). This sequence of different type pre-earthquake anomalies reveals the existence of successive pre-earthquake processes of a system which is moving towards a critical point which is the main shock.