Coda Q(c) attenuation and source parameter analysis in Friuli (NE Italy) and its vicinity

The digital data acquired by 16 short-period seismic stations of the Friuli -Venezia-Giulia seismic network for 56 earthquakes of magnitude 2.3-4.7 whi ch occurred in and near NE Italy have been used to estimate the coda attenu ation Q(c) and seismic source parameters. The entire area under study has b een divided into five smaller regions, following a criterion of homogeneity in the geological characteristics and the constrains imposed by the distri bution of available events. Standard IASPEI routines for coda Q(c) determin ation have been used for the analysis of attenuation in the different regio ns showing a marked anomaly in the values measured across the NE border bet ween Friuli and Austria for Q(0) value. A large variation exists in the cod a attenuation Q(c) for different regions, indicating the presence of great heterogeneities in the crust and upper mantle of the region. The mean value of Q(c)(f) increases from 154-203 at 1.5 Hz to 1947-2907 at 48 Hz frequenc y band with large standard deviation estimates. Using the same earthquake data, the seismic-moment, M-0, source radius, r a nd stress-drop, Delta sigma for 54 earthquakes have been estimated from P- and S-wave spectra using the Brune's seismic source model. The earthquakes with higher strcss-drop (greater than I Kbar) occur at depths ranging from 8 to 14 km.