Flandoli, Franco

Flank eruptions at Mt. Etna volcano are often related to the occurrence of strong earthquakes. Nevertheless, this is not always the case, and the relationship has to be modeled in probabilistic terms using Data Science. The topic has been investigated in a few studies, starting in the 80s and the 90s. This statistical analysis produced a clear result - the objective identification of the correlation of the two phenomena. However, from a quantitative point of view, the results were strongly affected by the limitations in the historical records available at that time, and by the statistical approaches adopted. The research continued afterwards, thanks to the basic research projects funded by the Department of Civil Protection in 2000-2015. This provided more complete and extended knowledge of the eruptive and seismic phenomena, and of their relationships. The implications for a multi-hazard assessment are significant. In particular, the quantitative analyses performed show that the probability of strong (i.e. damaging) earthquakes is influenced by the occurrence of flank eruptions for several weeks, both during the eruptive activity and after the end. The main target of the study is measuring and modeling how much is probable, if compared to the average pattern, to have an earthquake temporally related to a flank eruption, and how long this statistical influence can last for. In particular, we perform a time series analysis of both the seismic and eruptive records in the last 145-170 years, choosing the longest available seismic record which we assume to be complete. We included the estimation of the seismic rate and investigated the evidence for rate changes in time, as well as the effect of choosing different sub-records as a function of the scale parameters (e.g. earthquake magnitude thresholds, strain release). The key step in the study is the statistical analysis of the inter-event times, either between events of the same type or between earthquakes and eruptions. This produces quantitative estimates of the earthquake rate under the influence of flank eruptions, describing the behavior of the coupled volcano-tectonic system with the final purpose of performing a multi-hazard assessment. This research is currently funded by the Dipartimento della Protezione Civile (Italy), as part of the INGV-DPC contract 2019-2021.

Our study focuses on the estimation of the correlation between flank eruptions at Mt. Etna volcano and the pre-eruptive, syn-eruptive, and post-eruptive local seismicity, with the final purpose of improving the quantitative multi-hazard assessments. This research was motivated by the lateral eruption started at Etna on Dec. 24th 2018, that was followed by an intense seismic swarm producing a destructive earthquake (Mw 4.9, Dec. 26th) along the nearby Fiandaca fault. Indeed, earthquakes and eruptions at Etna are well known to be often occurring close in time, and a full probabilistic assessment would be very useful for civil protection purposes. The study relies on a few investigations developed in the 80s and 90s, which tested various statistical methods on the datasets available at that time, and the more recent research projects which provided more complete and extended databases on the eruptive and seismic phenomena. In particular, first we performed a time series analysis of both the seismic and eruptive records in the last 130-150 years, which are not affected by significant underrecording issues. We included the estimation of event rate and rate changes in time, and the description of spatial location and scale parameters (e.g. earthquake magnitude, erupted volume). Then, we accomplished a statistical analysis of the inter-event times, either between events of the same type, or between earthquakes and eruptions. Finally, we implemented a series of statistical tests aimed at the quantitative estimation of the correlation strength and its duration. The analyses were then conditioned on specific magnitude thresholds or spatial constraints (epicenters’ distribution vs eruptive fissure/vent location), with the purpose of further exploring the behavior of the coupled volcano-tectonic system.

Kick-off meeting Progetto B2 - Task 7 Stima quantitativa e modellazione della dipendenza statistica di sismicità ed eruzioni all’Etna, sulla base dei dati storici, con particolare attenzione al possibile legame tra terremoti maggiori ed eruzioni laterali Catania, 11 giugno 2019 – sede Osservatorio Etneo Task 2 – Analisi statistiche 11.45 Terremoti ed eruzioni all’Etna: R. Azzaro 11.55 Risultati del Progetto V4 Flank: S. Branca 12.05 Studi di letteratura e tecniche di analisi: A. Bevilacqua 12.25 Discussione