Three-Dimensional Crustal Structure in Southeastern Sicily (Italy) by Applying the Adaptive Mesh Seismic Tomography Method

Absolute and differential P- and S- wave data were used to invert Vp, Vp/Vs on a 3D grid of nodes and event locations in southeastern Sicily (Italy). The events selected have magnitude ranging between 1.0 and 4.2 and were recorded between 1994 and 2003 by a local network, consisting of nine digital 3-component stations. The adaptive mesh seismic tomography method (Zhang and Thurber, 2005) was applied by combining 3,474 absolute travel times and ~11,250 catalog-derived differential times of about 360 earthquakes. Unlike the most common tomography methods which use regular three-dimensional grid approaches, the adaptive mesh method is able to adapt the mesh nodes according to the changes of event locations and velocity structure. This capability is particularly useful when poor starting event locations and velocity model are available, since in these cases the ray distribution may change greatly during the inversion. The quality of the 3D model resulting from the tomographic inversion was evaluated on the basis of some synthetic tests. Moreover, comparison of the tomographic results with the tectonic map of the region has allowed satisfactory correlation of velocity anomalies with main tectonic faults. In particular, low velocity zones are found in the Ionian coast (inland and offshore), where several structures with NW-SE and NNE-SSW direction are present.