GNGTS 2015 - Atti del 34° Convegno Nazionale

2013 and the full seismicity of the year 2011. In overall, we identified 1960 phases (1350 P and 610 S) manually picked to avoid false detection that can be generate by the automatic STA/LTA trigger algorithm. All the data were recorded by Antelope ® , a software which represents an integrated set of programs that are able to acquire, store and process seismic devices. Method. We applied the Local Earthquake Tomography (LET) technique that represents an important tool for the Earth’s investigation. In this study, we used earthquake location method and travel time tomography combined in an iterative procedure. For event location, we adopted the Non-Linear Location NLLOC (Lomax et al. , 2009) that is a technique used to locate the events using the 3-D velocity model resulting from the tomographic inversion. This technique is formed by a set of programs for the creation of the grid location, the computation of travel times and the probabilistic, non-linear location of structures for 3-D data volume. As travel time tomography we adopted the software Cat3D, Computer Aided Tomography for 3-D models, developed by OGS (CAT 3D, User Manual, 2014) which computes the tomographic inversion of seismic waves travel times on 3-D models. In previous works, this software was mainly used for investigations in the field of exploration geophysics (Böhm et al. , 2006, 2009), while in other recent investigation (Tiberi, 2014), it is applied on seismological data. The main difference between active seismic and seismological applications is represented by the positions of sources, which in the first case are well defined, while for seismological purposes, they represents the unknowns parameters with high uncertainty. As inversion algorithm for the velocity estimation, in this work we adopted the SIRT (Simultaneous Inversion Reconstruction Technique) technique; this method is part of series expansion methods, on which the investigated area can be divided on elements with constant velocity, called pixel in 2-D or voxel in 3-D. The ray which links the source (earthquake location) Fig. 1 – a: In the black rectangle the zone of our investigation is represented. The red triangles indicate the stations of the CE3RN, the blue lines the sections extrapolated from our model. b: Zoom of the study area: rays’s coverage used for the tomographic inversion: with the red triangles are represented the stations included in our study area, while with the black dots are shown the event located using Non-Linear Location technique. 68 GNGTS 2015 S essione 1.2