GNGTS 2014 - Atti del 33° Convegno Nazionale

frequency (f0). The acquisition, with variable length between 30 and 45 minutes, was performed with a short period sensor (Lennartz LE-3D/5s (www.lennartz-electronic.de) coupled with a Reftek-130 datalogger (www.reftek.com) . The continuous signal has been subdivided into 60 s windows and the Fourier spectrum of each window has been calculated considering 1640 frequencies equally spaced in logarithmic scale between 0.01 and 20 Hz. The spectrum has been smoothed using the algorithm proposed by Konno and Ohmachi (2006), fixing the b parameter to 40. The vector composition of the Fourier spectra of the two horizontal components has been subdivided by the Fourier spectrum of the vertical component as proposed by Nakamura (1989, 2000) and the mean and the standard deviation of the ratios have been calculated. In order to compare the noise data with the geological setting the obtained F0 values have been interpolated to reconstruct lines with same value of f0 (Fig. 2). A progressive decrease of the resonant frequency (from 2 Hz to 0.37 Hz) is observed from S to N, which indicates an increasing depth of the sediments from Sulmona to the north (Pratola Peligna). In parallel, the resonant frequencies are progressively increasing from the basin centre to the basin edges (see HVSR data in Fig 1). The peaks observed in correspondence of the resonant frequency are well identifiable in the central part of the basin, indicating a strong impedance contrast between sediment and bedrock. At the base of the Mt. Morrone slope, the H/V curve has very low amplitudes (about 2.7) and the peak corresponding to the resonant frequency is hardly identifiable. Results of first level microzoning. The map of the homogeneous microzones in seismic perspective (MOPS) summarized the main results of the first level MS of Sulmona. This map, in fact, derives from the comparison of the geological, geothecnical and geophysical data and their integration with the values of the resonance frequencies obtained from the noise measurements. Considering that the urbanized areas and urban development lying almost completely above thick sequences of continental deposits (fluvial-lacustrine succession of the Fig. 2 – Thickness of the Plio-Quaternary continental deposits from gravimetric data (Di Filippo and Miccadei, 1997) and interpolated pattern of the resonant frequency f0, in Hz, obtained by noise measurements (this study). See text for explanation. 264 GNGTS 2014 S essione 2.2