Separation of depth-dependent intrinsic and scattering seismic attenuation in the northeastern sector of the Italian Peninsula

Abstract

We investigated the intrinsic dissipation and scattering properties of the lithosphere under the Friuli region (northeastern Italy) using two hypotheses: (i) a uniform earth model and (ii) wo 'reasonable' non-uniform, layered crustal models. For case (i) we measured the coda Q, and used the multiple-lapse time window analysis (MLTWA) technique to obtain separate estimates of intrinsic absorption and scattering attenuation. Results for the uniform earth model show that the lithosphere in northeastern Italy is characterized by a low-scattering attenuation (small scattering Q-inverse, Q1s), and by a relatively high intrinsic attenuation (high intrinsic Q-inverse, Q1i). A comparison between the investigated region and other areas around the world shows that both Q1i and Q1s for the Friuli region are among the lowest values ever measured, with the exception of the southern Apennines, which has the lowest measured Q1s. For case (ii), numerical simulation of the energy envelopes was performed using two-layered earth models, where the values of the intrinsic and scattering attenuation coefficients are both within 'reasonable ranges' when compared with the geological information. The theoretical envelopes calculated for the homogeneous model give a good fit to the synthetic envelopes calculated for the layered models; the best fit is obtained for scattering attenuation coefficients of the uniform model always greater than those of the layered model. The main result is consequently that scattering Q1s obtained using the MLTWA under the assumption of a uniform medium is overestimated, on average, by a factor 2. Finally, coda Q1 appears to be closer to the total Q1 than to the intrinsic Q1i, as predicted by the theory.