Qc, Qb, Qi and Qs attenuation parameters in the Umbria–Marche (Italy) region

Abstract

The attenuation of coda and S waves has been inferred for the Umbria–Marche region (central Italy) using seismic waveforms collected during the 1997 seismic crisis. The selected dataset is composed of 343 small magnitude (1.4 < ML < 4.2) earthquakes recorded at a temporary array composed of 23 seismic stations. The Sato (1977) method, based on the assumption of single isotropic scattering has been used to infer Qc, considering three different lapse times (20, 30 and 40 s). The coda normalization method (Aki, 1980) has been used to infer Qb. Both Qc and Qb show a clear frequency dependence with a different frequency dependent parameter. The frequency dependence of Qc is comparable with that previously found in the same area and around it. Using the method of Wennerberg (1993), intrinsic and scattering attenuation have been separated. Intrinsic attenuation is found to be close to coda attenuation and dominates over scattering dissipation. Coda Q increases with increasing lapse time but at a rate smaller than that observed in other areas of the Earth. Coda and intrinsic attenuation in the Umbria–Marche region are very high compared to other seismic active regions of the Earth. The retrieved high values of intrinsic attenuation may be explained in terms of the previously hypothesized fluid-pressurized regime of the crust in the central Apennines (Miller et al., 2004).