Tomographic images of a low velocity Vp and Vs volume beneath Stromboli Volcano, Italy

Reykjavik

The present study is mainly focused to determine the hypocentral locations and the velocity structure between the northeastern Sicily and southern Calabria, including the Aeolian Archipelago with particular regard to Stromboli volcano. The main goals are: i) to explore the differences between relative and absolute earthquake locations, ii) to identify spatial clusters in the seismicity, in order to investigate on the most active seismogenic zones and structures and iii) to recognize the presence of low velocity regions beneath the Aeolian Archipelago related to the presence of partial melting. We applied the TomoDD algorithm which use both absolute and differential arrival times to simultaneously determine event locations and Vp and Vp/Vs velocity models. 1,304 well located events have been considered during the 1994-2006 period. This code was applied to the catalog phase data, combining 11,261 P-wave and 5,751 S-wave arrival time differences. On the basis of the distribution of the events, a denser grid with respect to previous studies was used. This allowed a higher resolution of the velocity model and to find a better correspondence with the most active seismogenic zones and structures. Moreover, being the velocity structure of Stromboli poorly defined, a particular attention was devoted to this area. Tomographic images beneath this volcano revealed the presence of a low Vp and Vs (average values around 5.4 and 3.1 Km/s, respectively) elongated volume in the crust, suggesting the existence of partial melting. This volume extending until 17 km of depth, overlies a high Vp and Vs (values greater than 7.5 and 4.5 km /s, respectively) region that can be related to the Moho.