Attenuation of short-period seismic waves atMt 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 Q{1 C , the inverse of the quality factor for coda waves, for short lapse times (12 s), and Q{1 P and Q{1 S , the inverse of the direct body wave quality factors for P and S waves following shallow ray paths. We used the single scattering assumption to ¢t the amplitude envelopes of the coda at di¡erent frequency bands, obtaining aQ{1 C slowly varying with frequency, similar to values measured for other volcanoes at the same lapse time. Sitecorrected Q{1 P and Q {1 S 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 Q{1 P is 0:028 in both frequency bands, and Q{1 S is 0:015 and 0:017 at low and high frequencies respectively, almost independent of the frequency, and that the value of Q{1 P is about twice that of Q{1 S , as measured worldwide. A check was made by measuring the broadening of the ¢rst P-wave pulse with station^source distance, ¢nding Q{1 P ~0:024. Using the independent estimates of Q{1 C and Q {1 S , 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 con¢rms the hypothesis of the predominant role of the scattering phenomena with respect to the intrinsic dissipation in the seismogram formation for volcanic earthquakes.