Probing the Ionospheric Effects of the 2020 Aegean Sea Earthquake: Leveraging GNSS Observations for Tsunami Early Warning in the Mediterranean

Abstract On 30 October 2020, a Mw 7.0 earthquake occurred in the eastern Aegean Sea area north of Samos island (Greece), causing tsunami waves up to 3 m. In this work, we analyze Global Navigation Satellite System (GNSS) observations to investigate the induced ionospheric perturbation in total electron content (TEC) estimates. We observe TEC variations (up to 0.3 TECU), linked to the propagation of the internal gravity waves (IGWs) caused by the small tsunami. Comparison between IGWs arrival times in the ionosphere and the tsunami wave arrival at tide gauges reveals that the optimal observation geometries of ionospheric TEC detected the tsunami's arrival before it reached Kos and Hraklreio coastlines. We show that TEC variations, though slight, can be used to complement existing tsunami early warning systems, particularly in the Mediterranean region where such phenomena are not deeply investigated. Integrating TEC data alongside traditional seismic sensors and sea level measurements can assure a more robust early warning system capable of detecting and mitigating the effects of also small but impactful tsunamis.