Shallow shear-wave velocity structure of Solfatara volcano (Campi Flegrei, Italy),from inversion of Rayleigh-wave dispersion curves

摘要

In this work, we infer the 1D shear-wave velocity model at Solfatara volcano using thedispersion properties of Rayleigh waves generated by artificial explosions. The groupvelocitydispersion curves are retrieved by applying the Multiple Filter Technique tosingle-station recordings of air-gun sea shots. Seismic signals are filtered in differentfrequency bands and the dispersion curves are obtained by evaluating the arrival timesof the envelope maxima of the filtered signals. Fundamental and higher modes arecarefully recognized and separated by using a Phase Matched Filter. The dispersioncurves obtained indicate Rayleigh-wave fundamental-mode group velocities rangingfrom about 0.8 to 0.6 km/s over the 2-12 Hz frequency band. These group velocitydispersion curves are then inverted to infer a shallow shear-wave velocity model downto a depth of about 250 m. The shear-wave velocities thus obtained are compatiblewith those derived both from cross- and down-hole measurements in neighbouringwells and from laboratory experiments. These data are eventually interpreted in thelight of the geological setting of the area. Using the velocity model obtained, wecalculate the theoretical ground response to a vertically-incident S-wave getting two,main amplification peaks centered at frequencies of 2.2 and 5.4 Hz. The transferfunction was compared to those obtained experimentally from the application ofNakamura’s technique to microtremor data, artificial explosions and localearthquakes. Agreement among the experimental and theoretical transfer functions isobserved for the amplification peak of frequency 5.4 Hz.