GNGTS 2015 - Atti del 34° Convegno Nazionale

Local earthquake tomography in the junction between south-eastern Alps and External Dinarides using the seismic data of the CE3RN Network L. Colavitti 1 , L. Tiberi 1 , G. Böhm 2 , G. Costa 1 , A. Gallo 1 1 University of Trieste, Department of Mathematics and Geosciences, Seismological Research and Monitoring Group, Trieste, Italy 2 National Institute of Oceanography and Experimental Geophysics, Section of Geophysics, Trieste, Italy Introduction. The main force responsible of tectonic activity in south-eastern Alps is given by the collision between Adriatic microplate and Eurasian plate. This motion has a fundamental role in geodynamic evolution due to the convergence rate between Adria and Eurasian plate estimated greater than 2 mm/yr (Platt et al. , 1989). The largest historical earthquakes occurred in the region between Italy and Slovenia are reported in Burrato et al. (2008) and Galadini et al. (2005). Several large earthquakes hit the studied region in historical times, most of them were distributed in the Friuli Venezia Giulia region, as two events recorded in Tramonti in 1776 and 1794, but the most important earthquake that spread its effects in wide region was the 1511 Idrija event that represents the most destructive event that occurred so far in the region of the junction between south-eastern Alps and the External Dinarides, as reported in the catologues (Ribarič, 1982). In general, the area of Friuli Venezia Giulia region is characterized by a moderate seismicity, in fact the most important instrumental seismic event recorded in the area was the destructive 1976 Friuli earthquake with M s 6.5 (Aoudia et al. , 2000), that was widely studied thanks to the large amount of collected seismometric data. In Veneto region, seismicity normally decreases and the only destructive earthquake instrumentally recorded was the Cansiglio event with Mw 5.9 (Sirovich and Pettenati, 2004). Evidences that the collision is still active nowadays and the main seismogenic structures are located in the proximity of the political boundaries between Italy and Slovenia is also shown by the main shock of Bovec in April 1998 with M s 5.7 (Bajc et al. , 2001) and, later, in July 2004, with the event of Kobarid (M s 4.9), which generated a sequence that lasted until the end of November 2004 (Bressan et al. , 2009). It is evident that, in an area with complex seismogenic structures, the use of 1-D velocity model might not be sufficient, so defining a 3-D velocity model represents a better solution to understand the inner structure of the Earth. For this reason, we used the travel-time tomography technique to obtain an accurate 3-D velocity model: in this work, we used a Cat 3-D software to perform the travel time tomography and a non-linear location tool to define the position of the events. Data set. For the input parameters of our tomographic analysis it is fundamental to have a complete data set of available and accurate events in the area where potentially destructive events are located in the closeness of the political boundary between Italy and Slovenia. For this reason, seismic data were recorded by the Transfrontier network (Costa et al. , 2010), which is called Central Eastern European Earthquake and Research Network (CE3RN). This network was born thanks to a prolific cooperation of the governmental institutions of Italy, Austria, Slovenia and recently, Croatia, which decide to share in real time their seismological data for scientific purposes and for Civil Defense. The main importance of the CE3RN is to ensure a very good recording of the seismic events that occur very close to the political borders and that otherwise would be recorded in non-homogeneous way only by national networks; in this sense, the example of recent strong earthquakes demonstrated that this integration of services is essential for a rapid and efficient intervention (Bragato et al. , 2010). In Fig. 1a, the black rectangle shows the area of our investigation (longitude east between 12.5 and 14.5 ; latitude north between 46 and 46.5 ) while, red triangles represent the seismic stations which belong to the CE3RN network. For this study, we used 52 seismic stations and analyzed 180 earthquakes, including the events with magnitude more than 3 between 2004 and GNGTS 2015 S essione 1.2 67