Quantifying the Statistical Relationships Between Flank Eruptions and Major Earthquakes at Mt. Etna Volcano (Italy).

Bevilacqua, Andrea; Azzaro, Raffaele; Branca, Stefano; D'Amico, Salvatore; Flandoli, Franco; Neri, Augusto

At Mt. Etna volcano, flank eruptions are often accompanied by seismic swarms with damaging earthquakes; the most recent case‐history is the 2018 flank eruption, associated with a destructive earthquake (Mw 5.0). In this paper, we analyze the earthquake and eruptive catalogs from 1800 to 2018, to produce quantitative estimates of the earthquake rate under the influence of flank eruptions. We quantify that 30% of the flank eruption onsets precede a major (i.e., damaging, Ix ≥ V–VI EMS) earthquake by 30 days or less; 18% of the major earthquakes follow a flank eruption onset in 30 days or less. Thus, we show that the probability of major earthquakes increases 5–10 times after the onset of flank eruptions and this effect lasts for 30–45 days. This is also observed after the end of the eruptions. Results indicate different relationships depending on the location of the volcano‐tectonic systems considered individually (eruptive fissures, seismogenic faults). For instance, we describe a 10–20 times increased probability of earthquakes for 65–70 days after eruptions on the northeastern flank, and of new flank eruptions for 45–70 days after earthquakes of the Pernicana fault. Plain Language Summary: Historically, the flank eruptions of Mt. Etna have often been accompanied by destructive seismic events, although strong earthquakes have occurred during periods of volcanic quiescence too. As a result, the impact of both phenomena on local communities and territory is given by an alternation of two different hazards but still linked to each other. In this paper, by considering the up‐to‐date historical catalogs of earthquakes and eruptions at Mt. Etna, we quantify how probable it is, if compared to the average pattern, to have an earthquake temporally related to a flank eruption. That is, 30% of the flank eruption onsets precede a damaging earthquake by 30 days or less; the probability of strong earthquakes increases 5–10 times after the onset of flank eruptions and this effect lasts for 30–45 days. Thus, we show that the probability of damaging earthquakes drastically increases after the onset of flank eruptions and this effect lasts for several weeks. This is also observed after the end of the eruptions. Results provide the quantitative basis for a multihazard assessment that may enable better operative decisions to face future eruptive crises at Mt. Etna. Key Points: Flank eruptions at Mt. Etna are statistically compatible with Poisson processes with "slowly varying" rateThe major earthquakes and flank eruptions at Mt. Etna are not independentThe probability of major earthquakes increases by 5–10 times for 30–45 days after the onset and the end of a flank eruption

ETNA, Mount (Italy); VOLCANIC eruptions; EARTHQUAKE damage; EARTHQUAKES; POISSON processes; VOLCANOES; COMMUNITIES

Journal of Geophysical Research. Solid Earth, 2022, Vol 127, Issue 8, p1

2169-9313

Academic Journal

10.1029/2022JB024145