GNGTS 2014 - Atti del 33° Convegno Nazionale

TOMO-ETNA: an active seismic experiment at Etna volcano J. Ibáñez 1,2,3 , D. Patanè 1,3 , M. Coltelli 1 , F. Carrion 2,3 , P. P. Bruno 4 , O. Cocina 1 , L. Zuccarello 1 , A. Díaz-Moreno 2,3 , J. Prudencio 2,3 , F. Bianco 7 , D. Cavallaro 1,8 , M. Firetto Carlino 1 , C. Carmisciano 4 , L. Cocchi 4 , G. D’Anna 5 , B. Lhur 6 , TOMO-ETNA working group 1 Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania – Osservatorio Etneo, Catania, Italy 2 University of Granada, Granada, Spain 3 Instituto Andaluz de Geofisica, Granada, Spain 4 Istituto Nazionale di Geofisica e Vulcanologia, Roma 2, Roma, Italy 5 Istituto Nazionale di Geofisica e Vulcanologia, CNT, Roma, Italy 6 GFZ German Research Centre for Geosciences, Postdam, Germany 7 Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Napoli – Osservatorio Vesuviano, Napoli, Italy 8 Dipartimento di Scienze Biologiche, Geologiche e Ambientali – Sezione di Scienze della Terra, Università di Catania, Italy Mt. ������ �������� �������� �� ��� ������ �� � ������� ����������� ������� ����� ������ �� Etna’s eruptive dynamics is the result of a complex interaction between magma ascent in the plumbing system and the regional (deep crust) tectonic regime, together with local (shallow crust and volcanic edifice) structures partially controlled by flank instability. Magma ascent driving conditions (e.g., structural setting, tectonic forces) are not yet completely understood. The main limits in the understanding the eruptive dynamics of Etna volcano are largely due to the insufficient knowledge of its intermediate-deep crust, mostly based on passive seismic tomography and old active seismic experiments carried out more than twenty years ago (Colombi et al. , 1979; Sharp et al. , 1980; Hirn et al. , 1997). The old techniques for crustal imaging and their resolutions are unsuitable for the potential of current modelling and the comparison with the high quality of information provided by in-situ data sets of the volcano monitoring. Since 2000’s, recent tomographic inversions have progressively improved our knowledge of Etna’s shallow structure (down to 10 km depth), highlighting a complex pattern of magma reservoirs and conduits with variable dimensions and, consequently, the understanding of the most recent eruptions. However, the geometry of the conduits and the dimensions and shapes of small magmatic bodies still require greater investigation. An accurate imaging of the Etna’s plumbing system and the host crust is crucial to delineate a working model of this volcano in order to understand its behaviour and evolution of the ascent magma batches. At Mt. Etna, seismic tomography studies, based on natural seismicity and performed by using P and S-wave velocities, have shown that dike intrusion before eruptions can be associated with anomalous volumes of Vp/Vs in the shallow volcanic plumbing system (Patanè et al. , 2002, 2006). Low Vp/Vs anomalous regions were observed during both the July 2001 and the October 2002 dike intrusions feeding these two eruptions (Patanè et al. , 2002). Patanè et al. (2006) observed Vp/Vs time dependent anomalies by 4D tomography, between the 2001 and 2002–2003 eruptive period, interpreting it as the trace of fluid intrusion (gas-rich magma ) and gas migration from the shallow magma body in the upper cracked volume that develops during the eruptive period. By studying the attenuation of P-waves (Qp), Martinez-Arevalo et al. (2005) and De Gori et al. (2011), identified the location and extent of magma bodies during the 2001 and 2002–2003 eruptions. More recently Alparone et al. (2012), investigating the mechanisms of the 2008-2009 flank eruption, calculated 3D velocity and attenuation tomography, including a 3D relocation of the used seismic events. The most important result obtained from the joint analysis of Vp, Vp/Vs and P-wave attenuation is an anomalous zone with normal to high Vp and low Vp/Vs, which partially overlaps a low Qp volume located along a NS trending “channel” beneath the summit craters. This can be interpreted as a shallow volume characterized by high temperature where the magma including supercritical fluids is located. At present, the emplacement of shallow dikes that feeding eruptions along the NNW-trending fracture system (S Rift) and along the NE Rift, seems to occur prevalently at the western border of a wide high Vp velocity body (HVB). The HVB is centered in the Valle del Bove with a NNW-SSE to NS orientation, between -1 and -7 km depth (slight rotated at greater depth). This volume is mainly aseismic and seismicity is located around it, mainly to the west and east�. 218 GNGTS 2014 S essione 1.3