GNGTS 2013 - Atti del 32° Convegno Nazionale

The tomographic method and inversion strategy. The method performs a simultaneous inversion of P- and S-arrival times to estimate the event location coordinates, origin times and P and S velocities at the nodes of a 3D discretized volume. The forward problem, e.g. the travel- time calculation, is solved by preliminary using the finite-difference solution of the eikonal equation and a re-calculation by integration of slowness along the ray path. This procedure makes the travel-time estimation less sensitive to the grid discretization. The inversion strategy is based on a multiscale approach (Chiao and Kuo, 2001) according to which a series of inversion runs are performed by progressively decreasing the velocity model grid spacing. At each step, the starting model is fixed at the one obtained in the previous step but using a larger grid size. This allowed to first estimate the large wavelength components of the velocity model and then to progressively introduce the smaller-scale components for the model reconstruction. Fig. 2 – Map view of the P-wave tomographic model at each parametrization. 8 GNGTS 2013 S essione 1.1