Attenuation of short-period seismic waves at Mt Vesuvius, Italy

We analysed short-period seismograms from about 250 very local events recorded by a network of high dynamic range short-period seismic stations deployed on Mt Vesuvius to estimate the site-corrected short-period seismic attenuation. We calculated QC− 1, the inverse of the quality factor for coda waves, for short lapse times (12 s), and QP− 1 and QS− 1, the inverse of the direct body wave quality factors for P and S waves follow- ing shallow ray paths. We used the single scattering assumption to fit the amplitude envelopes of the coda at different frequency bands, obtaining a QC− 1 slowly varying with frequency, similar to values measured for other volcanoes at the same lapse time. Site-corrected QP− 1 and QS− 1 were estimated using the frequency decay method for both P and S waves in two frequency bands, 1–6 Hz and 15–24 Hz. Results show that QP− 1 is 0.028 in both frequency bands, and QS− 1 is 0.015 and 0.017 at low and high frequencies respectively, almost independent of the frequency, and that the value of QP− 1 is about twice that of QS− 1, as measured worldwide. A check was made by measuring the broadening of the first P-wave pulse with station–source distance, finding QP− 1=0.024. Using the independent estimates of QC− 1 and QS− 1, we separated the intrinsic from the scattering quality factor at Mt Vesuvius, obtaining a high scattering and a low intrinsi c Q− 1, as already observed for other volcanoes. This result confirms the hypothesis of the predominant role of the scattering phenomena with respect to the intrinsic dissipation in the seismogram formation for volcanic earthquakes.