Array and spectral ratio techniques applied to seismic noise to investigate the Campi Flegrei (Italy) subsoil structure at different scales
2020
Abstract. The purpose of this work is to study the subsoil
structure of the Campi Flegrei area using both spectral ratios and array
techniques applied to seismic noise. We have estimated the dispersion curves
of Rayleigh waves by applying the Frequency–Wavenumber ( f – k hereinafter)
and Modified Spatial Autocorrelation (MSPAC) techniques to the seismic noise
recorded by the underground short period seismic Array “ARF”, by the
broadband stations of the UNREST experiment and by the broadband stations of
the seismic monitoring network of INGV – Osservatorio Vesuviano. We have
performed the inversion of a dispersion curve (obtained averaging the f – k
and MSPAC dispersion curves of seismic noise and single phase velocity
values of coherent transient signals) jointly with the H∕V spectral ratio of
the broadband station CELG, to obtain a shear wave velocity model up to 2000 m depth. The best-fit model obtained is in a good agreement with the
stratigraphic information available in the area coming from shallow
boreholes and deep wells drilled for geothermal exploration. In active
volcanic areas, such as Campi Flegrei, the definition of the velocity model
is a crucial issue to characterize the physical parameters of the medium.
Generally, a high quality characterization of the medium properties helps to
separate the contributions of the volcanic source, path and site in the
geophysical observables. Therefore, monitoring possible variations in time
of such properties in general can help to recognize anomalies due to the
volcano dynamics, i.e. fluid migration connected to the volcanic activity.
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