Separation of intrinsic and scattering seismic attenuation in the Southern Apennine zone, Italy

Abstract

Scattered waves observed at the seismographs of the National Italy's seismic network have been used to investigate the intrinsic dissipation and scattering properties of the lithosphere under the Southern Apenninnes, Italy. First, we investigate the coda-Q properties, then we apply the MLTW analysis in the hypothesis of velocity and scattering coefficient constant with depth, and finally we interpret these results with the aid of numerical simulations in a medium with depth dependent velocity and scattering coefficient. Results obtained in the hypothesis of a uniform model show that a low scattering-Q -1 and a relatively higher intrinsic-Q -1 characterize the lithosphere of the Southern Apennines. Numerical simulations of the seismogram energy envelopes were performed hypothesizing a strongly scattering crust and trasparent upper mantle, both with reasonable intrinsic dissipation coefficients. In these symplifying assumptions the theoretical curves calculated for the homogeneous model fit to the synthetic envelopes with scattering attenuation coefficients always greater than the synthetic values. This results lead to the consideration that scattering-Q -1 obtained using MLTW analysis under the assumption of uniform medium are overestimated. The values of the scattering-Q -1 estimated for Apennines at low frequency (1-2 Hz) in the hypothesis of uniform medium are of the same order of those obtained in several areas around the world. The estimates obtained for frequencies ranging from 2 to 12 Hz are very low if compared with those obtained in the same hypothesis for other areas around the world. Coda Q -1 closely resembles intrinsic Q -1.