GNGTS 2013 - Atti del 32° Convegno Nazionale

the chain and the Ionian offshore, through the integration of seismic and GPS-based geodetic observations, collected in nearly two decades. In particular, we carried out a simultaneous inversion of both the three-dimensional velocity structure and the distribution of seismic foci to define the geometry of seismogenic structures responsible of this seismicity. The computation of fault plane solution for the major and best recorded earthquakes was of great importance for the characterization of seismogenic sources and the orientation of the crustal stress field acting in the area. The comparison of these findings with the GPS-based ground deformation will help to improve the knowledge of the investigated area. Seismic data. About 1020 small-to moderate-magnitude earthquakes (1.0 ≤ M L ≤ 4.6), re- corded between 1994 and 2013 by a local network, were selected from the “Catalogo dei ter- remoti della Sicilia Orientale - Ca- labria Meridionale. INGV, Catania” (Gruppo Analisi Dati Sismici, 2013). In particular, the events have been employed as data source for simultaneous inversion of both a 3-D velocity structure and the hy- pocentre parameters by the code to- moDDPS (Zhang et al. , 2009). With respect to more simple algorithms, this code has the ability to improve the accuracy of event locations and to sharpen the velocity images near the source region because of the combination of absolute and differ- ential arrival times. For the tomography, we filtered the initial dataset according to the quality criteria of location. In par- ticular, we selected only well lo- cated events, i.e. those with at least nine observations (P- and S-phases), root-mean-square (RMS) residuals smaller than 0.35 s and horizontal and vertical location errors lower than 2.5 km and 4.5 km, respectively. Finally, about 880 earthquakes with Fig. 1 – a) Simplified tectonic map of Sicily. b) Relocated seismicity (see text for further details). c) Vertical sections through the VP model. The traces of sections are report- ed in the map (b) with blue lines. Contour lines are at an interval of 0.25 km/s and the relocated earthquakes, within ±10 km from the sections are plotted as grey cir- cles. HMEFS, Hybleo-Maltese Escarpment Fault System; SLG, Scordia-Lentini Gra- ben; AB, Augusta basin; FB, Floridia ba- sin; SRFS, Scicli-Ragusa Fault System; AF, Alfeo seamount. 216 GNGTS 2013 S essione 1.2