Source scaling and site effects at Vesuvius volcano

The site-corrected source scaling pattern is estimated for local earthquakes(0:9 ≤MD ≤ 3:6) at Mt. Vesuvius. The dataset comprises 35 low-to-moderatelocal earthquakes recorded by 14 three-component seismic stations during 1993, 1996, and 1999.Site-transfer functions in the frequency range 1 Hz–25 Hz are estimated from thespectra of S waves and coda waves and from the horizontal-to-vertical (H=V) spectralratios. We applied the direct spectral ratios method to S waves, considering as a reference the average spectrum and the inversion method to S waves and coda waves.The site amplification on the coda waves was also compared with that evaluated usingthe wavelet transform. The standard deviation associated with the experimental resultsis computed for all of the used methods.Results indicate a general agreement among the methods, and the site-transferfunctions show interesting features. The highest amplifications are found for frequencies lower than 12 Hz for sites located at lower altitude. The methods based on coda waves show highest amplification with respect to the methods based on S waves for most of the sites located in the summit part of the volcano. This can be a phenomenon of coda localization, which consists in the trapping inside the upper part of the volcano of scattered waves. The H=V spectral ratios do not show total agreement with the othermethods, mostly for the sites located in the summit part of the volcano. The discrepanciesamong the results obtained in this work are also due to the different normalizationapplied in the methods of analysis.Generalized inversion method allowed us to estimate the source scaling of thesite-corrected source seismic spectrum for the investigated area. The source scalingobtained in terms of seismic moment and source radii shows that the seismicity ofMt. Vesuvius is characterized by stress drop as low as a few bars (10 bars) exceptfor the event of MD 3:6 (Δσ 100 bars). The scaling pattern shows an apparentlinear relationship between source size and seismic moment (for MD ≤ 3:3) but thestatistical test shows that the linear trend has low reliability.