Abstract
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.
Highlights
The Campi Flegrei Caldera (Fig. 1) has been the scenario of two high magnitude, caldera-forming eruptions: the Campanian Ignimbrite (IC) and the Neapolitan Yellow Tuff (NYT), occurred 39 ka ago and 15 ka BP, respectively
Nardone et al (2017), using ambient noise records of ARF array jointly inverted with H /V ratio of coda waves of earthquakes recorded at CELG station, obtained a preliminary model composed of three main layers over a half-space with a shear-wave velocity increasing with depth
In this work we provide a more detailed velocity model for the central part of the Campi Flegrei caldera using surface wave dispersion and spectral ratio of seismic noise
Summary
The Campi Flegrei Caldera (Fig. 1) has been the scenario of two high magnitude, caldera-forming eruptions: the Campanian Ignimbrite (IC) and the Neapolitan Yellow Tuff (NYT), occurred 39 ka ago and 15 ka BP, respectively. The outcropping rocks are composed by continental and marine sediments intercalated with pyroclastic deposits mainly emplaced by pyroclastic density currents in the proximal areas, and by pyroclastics fallout in the distal ones (Orsi et al, 2004, and references therein). These deposits are composed by loose pyroclastic material (ash, pumice, scoriae, lithics) or lithified tuffs and minor lavas. These sequences are intercalated, in the lowlands, with marine and coastal sediments (Di Vito et al, 1999). The caldera structure has been object of several scientific studies aimed at the investigation of different and complementary parameters: identification of volcanic tremor of hydrothermal origin
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