The Stromboli geophysical experiment: preliminary results on the STRO-06 oceanographic cruise (Multibeam bathymetry and wide-angle refraction seismics)

The Stromboli geophysical experiment, performed to acquire onshore and offshore seismic data through a combined on-land and marine network, was finalized to reconstruct the seismic tomography of the volcano and to investigate the deep structures and the location of the magma chambers (Marsella et al., 2007; Castellano et al., in press.). The STRO-06 oceanographic cruise (December 2006) was carried out in the framework of the "INGV-DPC V2 Monitoring and Research Activity at Stromboli and Panarea - Unit V2-03" and resulted as a joint initiative between CNR (IAMC, Napoli and ISMAR, Bologna), INGV (Roma2, Osservatorio Vesuviano, Catania, Gibilmanna-CNT), University of Firenze and DPC. A detailed Multibeam swath bathymetry around the Stromboli volcano has been acquired by using the Multibeam RESON 8160, in dotation to the R/V Urania (National Research Council of Italy), integrating Multibeam bathymetric datasets previously collected by CNR-ISMAR (Bortoluzzi et al., 1999). Detailed swath bathymetry of the "Sciara del Fuoco" area allowed to image the present-day seafloor setting of the area involved by the submarine slide of 30-12-2002 (Bonaccorso et al.., 2003). During the experiment wide angle refraction seismics was performed all around the Stromboli volcano by a 4 GI-GUN tuned array. The data were recorded by the permanent seismic network of the INGV and 20 temporary stations (positioned for the experiment) and 10 OBS deployed on the SE, SW and NE submerged flanks of the volcano after detailed morpho-bathymetric analysis. A high velocity area living in the SE Tyrrhenian sea has been interpreted by tomographic studies as the Ionian slab subducting toward NW (Cimini, 2004; Lucente et al., 1999). The slab shows an evident lateral continuity with high dipping angles down to 400 km depth and lateral extension of 200 km deeper than 150-200 km and 100 km above (Montuori, 2004). Low velocity zones are present along the whole vertical extension of the high velocity zone, being interpreted as astenospheric fluxes or convective cells generated by the subducting plate. The coincidence between the observed low velocity zone and the morphology of the Aeolian arc indicates that subduction was able to generate regional volcanism. The Stromboli volcanic edifice (Di Fiore et al., 2006) was recently considered to be similar to the Campanian volcanoes with well developed, 10-15 km thick low velocity strata and a thin continental crust superimposed (Panza et al., 2004). The poliphasic eruption activity (Beccaluva et al., 1985) intercalated lava strata (high velocity, 2500-4000 m/sec) to pyroclastic explosive products strata (P wave velocity 300-800 m/sec) causing strong vertical and horizontal velocity gradients. The products continuously erupted by the Stromboli volcano onlap on its submarine flanks and are often subject to submarine gravity instabilities. The eastern flank of the island shows a large chute of detritus, triggered by channelised debris fluxes organized as large-scale sea bottom features perpendicular to the isobaths. The northwestern sector is occupied by the submarine continuation of the "Sciara del Fuoco", extending for several kilometers before joining laterally the Stromboli canyon. Detailed DEM of the S-SE flank of Stromboli edifice (fig. 1) evidences an irregular sea bottom morphology, characterized by outcrops of volcanic acoustic basement, separated by NE-SW trending lineaments, resulting from channelised flows of volcanoclastic deposits towards the slope and the bathyal plain. Detailed DEM of the SW flank, connecting Stromboli to Panarea (fig. 2) shows a more regular morphology. Rounded-shaped morphology are interpreted as volcanic blocks deposited after mass wasting along the slope, while E-W trending lineaments represent a dr