High frequency attenuation k parameter and QS 3D model for south-eastern Alps and north-western Dinarides

We estimated the spectral decay parameter k using waveforms produced by small-tomoderate earthquakes in the time period 1994-2011 in NE Italy and western Slovenia. We reconstructed the 3D distribution of the frequency independent part of the S waves′ quality factor, Q_S, by using k values and S waves velocity V_S values as input. The Q_S model presented marked lateral and depth variations with a zone of low Q_S in the Kobarid area (western Slovenia). Considering these data together with available 3D distribution of V_P, V_P/V_S and shear modulus, we hypothesize that this is a highly fractured area permeated by fluids with variable pore pressure. At depths of 6-9 km, both in the central and in the western part of the area under study, two regions are characterized by significant lateral and in-depth Q_S contrasts. We interpreted these results in terms of amount of crack density and geological units.