Investigating Ionospheric Disturbances from the 2020 Samos Earthquake and Tsunami: Advancing GNSS-Based Tsunami Early Warning in the Mediterranean

The study of signatures in the ionospheric total electron content (TEC) related to seismic events such as earthquakes and tsunamis, has predominantly focused on significant, high-impact occurences, such as the 2004 Sumatra earthquake and tsunami (Mw 9.2) [2] or the 2011 Tohoku-Oki event (Mw 9.0) [3]. These generate clear signatures in TEC time series, that can offer valuable insights in enhancing early warning systems for tsunamis. However, despite the knowledge gained from these significant events, there remains a crucial gap in the literature concerning smaller-scale seismic events presenting Mw7 and few meters high tsunami waves. Indeed, while earthquakes with Mw around 7 are not considered small in a general sense, they are relatively minor in terms of their ability to generate pronounced ionospheric perturbations. Nevertheless, their study is equally important due to their potential for significant impact on humans and the environment. This has been demonstrated in seismic regions like the Mediterranean Sea, where the tsunami waves are amplified by narrow straits and coastal configurations, making even smaller events highly destructive. This underscores the critical need for studies focused on smaller yet impactful events to improve real-time tsunami early warning systems. 

Motivated by the seismic nature of the Mediterranean region, marked by small-scale earthquakes and tsunamis from a ionospheric point of view,we carried out the study related to the detection of the small signatures generated in the ionosphere by the Samos earthquake and tsunami that occurred on 30 October2020 (Mw 7.0), causing tsunami waves up to 3 m. This study examines Global Navigation Satellite System (GNSS) data to analyze the resulting ionospheric disturbances in total electron content (TEC) measurements. We detected TEC variations of up to 0.3 TECU, associated with the propagation of internal gravity waves (IGWs) triggered by the small tsunami. By comparing the IGWs' arrival times in the ionosphere with tsunami wave arrivals at tide gauges, we found that optimal ionospheric TEC observation geometries detected the tsunami's presence before it reached the Kos and Heraklion coastlines. Our findings demonstrate that even small TEC variations can complement existing tsunami early warning systems. This is particularly valuable in the Mediterranean region, where such phenomena remain underexplored. Integrating TEC data with traditional seismic sensors and sea level measurements can enhance early warning systems, improving their capacity to detect and mitigate the effects of small but significant tsunamis.

The results are published in Fuso & Ravanelli (2024) [1].

[1] Fuso, F., & Ravanelli, M. (2024). Probing the ionospheric effects of the 2020 Aegean Sea earthquake: Leveraging GNSS observations for tsunami early warning in the Mediterranean. Journal of Geophysical Research: Space Physics, 129(12), e2024JA032946.

[2] Occhipinti, G., Lognonné, P., Kherani, E. A., & Hébert, H. (2006). Three‐dimensional waveform modeling of ionospheric signature induced by the 2004 Sumatra tsunami. Geophysical research letters, 33(20).

[3] Occhipinti, G., Rolland, L., Lognonné, P., & Watada, S. (2013). From Sumatra 2004 to Tohoku‐Oki 2011: The systematic GPS detection of the ionospheric signature induced by tsunamigenic earthquakes. Journal of Geophysical Research: Space Physics, 118(6), 3626-3636.