Volcanological inferences from seismic-strain tensor computations at Mt. Etna Volcano, Sicily

Abstract

Kostrov's (1974) algorithm for seismic-strain tensor computations, in the version implemented by Wyss et al. (1992a) for error estimates, has been applied to shear-type earthquakes occurring beneath the Etna volcano during 1990±1996. Space±time variations of strain orientations and amplitudes have been examined jointly with ground-deformation and gravimetric data collected in the same period and reported in the literature. Taking also into account the information available from volcanological observations and structural geology, we propose a model assuming that hydraulic pressure by magma emplaced in nearly north±south vertical structures produces the E±W orientation of the maximum compressive strain found in the upper 10 km beneath the crater area. In contrast, regional tectonics deriving from the slow, north± south convergence between the African and European plates appear to play a dominant role in the generation of stress and strain fields at crustal depths deeper than 10 km below the volcano. According to our interpretation, the progressive ascent of magma through the upper crust prior to eruption produces the observed gravity changes, cone inflation and unusual seismic strain rate in the upper 10 km associated with a more sharply defined seismic deformation regime (i.e. very small confidence limits of the e 1 orientation).In agreement with this model, deflation revealed by ground-deformation data during the course of the major 1991±1993 eruption was accompanied by a practically nil level of shallow seismicity.

Influence of substrate tectonic heritage on the evolution of composite volcanoes: Predicting sites of flank eruption, lateral collapse, and erosion

“…and one of the most active, has arisen rapidly from a succession of overlapping central vents and associated flank eruptions in approximately the last 200 ka (Romano, 1982;Calvari et al, 1994;Coltelli et al, 1994;Corsaro et al, 2002;Branca et al, 2004). According to Lanzafame et al (1997a), Barberi et al (2000) and Patanè and Privitera (2001) the stress and strain field at Mt. Etna are homogeneous in the western sector at depths greater than 10 km; in particular, the main compressive stress and strain axes are almost horizontal and trending about N-S.…”

Regimes of magma recharge and their control on the eruptive behaviour during the period 2001–2005 at Mt. Etna volcano

“…If the magma is not connected with the open and steadily degassing conduit, the retained gas raises the overpressure within the melt, which can attain a compressible state (Huppert and Woods 2002). Data on the seismic strain indicate that above 10 km of depth, strain could be driven by magma overpressure acting on the seismogenic structures (Cocina et al 1998;Barberi et al 2000Barberi et al , 2004. Under such conditions, even relatively small perturbations (e.g., low magnitude earthquakes) can generate a massive gas exsolution, potentially triggering highly explosive eruptions.…”

Evidence of multiple strain fields beneath the eastern flank of Mt. Etna volcano (Sicily, Italy) deduced from seismic and geodetic data during 2003–2004

“…More details about stress fields in the Etnean region are reported in Cocina et al (1998), Barberi et al (2000) and Barberi et al (2004). In order to define discrepancies between the stress tensor and focal plane solutions, a misfit (F) variable is introduced.…”