SEISMIC NOISE AT SOLFATARA VOLCANO (CAMPI FLEGREI, ITALY): ACQUISITION TECHNIQUES AND FIRST RESULTS

In the period 2-6 April 2007 a seismic survey was carried out at Solfatara Volcano, with the aim of inferring the shallow structure and evaluating local site effects. Seismic noise was recorded by five circular seismic arrays deployed in different areas of the crater. The geometry was designed in order to obtain also a sub-configuration consisting of two profiles oriented in the NS and E-W directions. An other seismic station was installed on the eastern rim of the crater, for a hardrock reference. A preliminary spectral analysis was performed on some samples of seismic noise recorded during the experiment. As future development, surface wave dispersion will be obtained by using array techniques, such as the Spatial Autocorrelation method (SPAC) of Aki (1957) and its recent modifications (MSPAC, Bettig et al, 2001; CCA, Cho et al., 2004). The shear-wave velocity models will be inferred for each array from the inversion of the dispersion curves. Moreover experimental site transfer functions will be evaluated for each station, using both Nakamura's technique and the reference-site spectral ratio method. The high density of the deployment and the large number of the sampled sites will allow to obtain a detailed shallow velocity structure and to map resonance frequencies and amplification values in different areas of the crater.