Magma intrusion mechanisms and redistribution of seismogenic stress at Mt. Etna volcano (1997-1998)

Several volcanoes worldwide have shown changes in their stress state as a consequence of the deformation produced by the pressurization of a magmatic body. This study investigated seismic swarms occurring on the western flank of Mt. Etna in January 1997-January 1998. Integrating seismic observations and geodetic data, we constrained the seismogenic fault system, and on the basis of stress tensor inversion and SH(MAX) analyses, we inferred an inflating pressure source located at 5.5 km b.s.l. beneath the west portion of summit area. Evaluation of Coulomb failure stress related to the proposed model showed how a large part of the seismogenic fault underwent a significant Coulomb failure stress increase (500 kPa). We inferred the presence of a sub-vertical faulted region, potentially weak, N50 degrees E-oriented beneath the western sector of Mt. Etna. This structure could be brought closer to failure, thereby generating seismic swarms as the effect of elastic stress transfer induced by movement and/or overpressure of magmatic masses within the upper crust under the volcano.