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

Abstract

We carried out a study of the seismicity and ground deformation occurring on Mt. Etna volcano after the end of the 2002-2003 eruption and before the onset of the 2004-2005 eruption. Data were recorded by the permanent local seismic network run by Istituto Nazionale di Geofisica e Vulcanologia -Sezione di Catania and by geodetic surveys carried out in July 2003 and July 2004 on the GPS network.Most earthquakes were grouped in two main clusters located in the northeastern and southeastern sectors of the volcano. The areal distribution of seismic energy associated with the recorded earthquakes allowed us to highlight the main seismogenic areas of Mt. Etna. In order to better understand the kinematic processes of the volcano, 3D seismic locations were used to compute fault plane solutions, and a selected dataset was inverted to determine stress and strain tensors. The focal mechanisms in the northeastern sector show clear left-lateral kinematics along an E-W fault plane, consistent with events occurring along the Pernicana Fault system. The fault plane solutions in the southeastern sector show mainly right-lateral kinematics along a NNE and ENE fault plane and left lateralkinematics along NW fault planes that together suggest roughly E-W oriented compression. Surface ground deformation affecting Mt. Etna measured by GPS surveys highlighted a marked inflation during the same period and exceptionally strong seawards motion of its eastern flank.The 2D geodetic strain tensor distribution was calculated and the results show mainly ENE-WSW extension coupled with WNW-ESE contraction, indicating right-lateral shear along a NW-SE oriented fault plane. The different deformation of the eastern sector of the volcano, as measured by seismicity and ground deformation, must be interpreted by considering the different depths of the two signals. Seismic activity in the southeastern sector of volcano is located between 3 and 8 km b.s.l. and can be associated with a very strong additional E-W compression induced by a pressurizing source just westwards and at the same depth, located by inverting GPS data. Ground deformation, in contrast, is mainly affected by the shallower dynamics of the fast moving eastern flank which produces a shallower opposing E-W extension. The entire dataset shows that two different processes affect the eastern flank at the same time but at different depths; the boundary is clearly located at a depth of 3 km b.s.l. and could represent the décollement surface for the mobile flank.

Tilt offset associated with local seismicity: the Mt. Etna January 9, 2001 seismic swarm.

“…[51,52]). , it was more deeper than the detachment surface of the eastern flank [22] and seems to have tectonic features rather than volcanic. An analysis of tilt data help to exclude the presence of magma.…”

“…A local stress, induced by the recharge that preceded the Mt. Etna 2001 eruption [22], is the most reliable source of the dislocation. The variations recorded between 03:00 and 3:30 at the three tilt stations (Fig.…”

“…[20,21]) and the décollement surface is located at a depth of 3 km b.s.l. ( [22] and references therein).…”

“…In particular, seismic activity in the southeastern sector of volcano, located between 3 and 8 km b.s.l., has been associated with an E-W compression induced by a pressurizing source just westwards and at the same depth [22].…”

Why Does a Mature Volcano Need New Vents? The Case of the New Southeast Crater at Etna

“…The ground deformation here analyzed has been previously described in terms of displacements of the measurement stations (Bonforte et al, 2008Bonaccorso et al, 2011Bonaccorso et al, , 2015. Conversely, here we calculate the horizontal strain tensor components by the GridStrain routine developed by Pesci and Teza (2007), already used for investigating the surface deformation of the eastern flank of Etna by Alparone et al (2011). This algorithm allows us to analyse the strain tensor distribution over an area covered by a geodetic network, starting from station displacements.…”