Abstract
We investigated the relation between the surface deformation and seismicity caused by dike propagation. In a previous study, Bonaccorso et al. (2017) found a simple but effective equation that relates the average thickness and dimension of the dike with the expected released mechanical energy and, therefore, to the seismic moment. In the early morning of 24 December 2018, the shallow portion of Etna volcano was suddenly crossed by a violent dike intrusion that, after few hours, reached the summit area and opened an eruptive fissure feeding a lava flow. The intrusion was accompanied by an intense seismic swarm, with hypocenter located beneath the summit craters and along the eruptive fracture, and by ground deformation inferring a tensile source of the eruptive dike. The seismicity also continued the following day, with a deepening of the hypocenters up to 3 km b.s.l. as a response to the onset of a further deeper intrusion which sought to penetrate the volcano edifice without reaching the surface. This situation generated the fear of potentially critical consequences of feeding a more dangerous eruption in the medium-low flanks. In this study, we analyze the balance between deformation caused by the modeled dikes and the released seismic energy by following the above-mentioned approach. It proved very useful in the specific case of Etna volcano eruptions, resulting an effective tool to monitor the state of the intrusion of the magma, and to evaluate if this intrusion has enough energy to continue propagating or to sto
Highlights
Dike propagation is a main process for magma transport and eruptions
The eruption of Christmas 2018 was a peculiar event for two main aspects: i) in spite of a powerful intrusion, the ensuing effusive activity lasted only about 3 days, stopping on the morning of December 27; ii) it was accompanied by a seismic swarm that did not stop after the start of the eruption but continued until the afternoon of the following day
The continuation of seismicity was associated with the propagation of a second deeper dike, which was unable to reach the surface but stopped 1.5 km below the crater area
Summary
Dike propagation is a main process for magma transport and eruptions. Several studies have investigated this mechanism involving different approaches such as solid mechanics, field mapping and analogue lab experiments. The authors obtained a linear relation between log Mo and log10UT, where Mo is the cumulative recorded seismic moment and UT the total 3D available mechanical elastic strain energy, obtained multiplying the UE of Eq 1 by the length of the dike in the direction perpendicular to the propagation (i.e., the estimated width) The purpose of this result is to obtain a tool for tracking the energy released by the intrusion to evaluate its propagation. After the start of the eruption and until the afternoon of December 25, a second dike penetrated the high southern eastern flank but did not reach the surface (dike II) This dike was very thick (∼5 m opening) and deeper, departing from about 3 km b.s.l. and stopping inside the volcano edifice at 1.5 km a.s.l. The parameters of the dikes modeled by Aloisi et al (2020) are reported in Supplementary Table S2. The cumulative energy released until the afternoon of December 25 reaches the value of 1.16 × 1016 J
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