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

We analysed short-period seismograms from about 250 very local events recor ded by a network of high dynamic range short-period seismic stations deploy ed on Mt Vesuvius to estimate the site-corrected short-period seismic atten uation. We calculated Q(C)(-1), the inverse of the quality factor for coda waves, for short lapse times (12 s), and Q(P)(-1) and Q(S)(-1), the inverse of the direct body wave quality factors for P and S waves following shallo w rah paths. We used the single scattering assumption to fit the amplitude envelopes of the coda at different frequency bands, obtaining a Q(C)(-1) sl owly varying with frequency, similar to values measured for other volcanoes at the same lapse time. Site-corrected Q(P)(-1) and Q(S)(-1) were estimate d 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 Q(P)(-1) is 0.028 in bot freq uency bands, and Q(S)(-1) is 0.015 and 0.017 at low and high frequencies re spectively, almost independent of the frequency, and that the value of Q(P) (-1) is about twice that of Q(S)(-1), as measured worldwide. A check was ma de by measuring the broadening of the first P-wave pulse with station-sourc e distance, finding Q(P)(-1) = 0.024. Using the independent estimates of Q( C)(-1) and Q(S)(-1), we separated the intrinsic from the scattering quality factor at Mt Vesuvius, obtaining a high scattering and a low intrinsic Q(- 1), as already observed for other volcanoes. This result confirms the hypot hesis of the predominant role of the scattering phenomena with respect to t he intrinsic dissipation in the seismogram formation for volcanic earthquak es.