A review of nonparametric attenuation functions computed for different regions of Italy

We used a set of previously published nonparametric attenuation functions to calculate average functions for the Italian region. These nonparametric functions describe the spectral amplitude decay of the S waves as a function of distance for 14 frequencies between 1 and 20 Hz for the regions of Lombardia-Piemonte, Eastern Sicily, Friuli, Marche and the Central Apennines. Since all the attenuation functions were obtained using the same methodology, we were able to make a fair comparison of the attenuation characteristics of the different regions. In general, while the Central Apennines show the strongest amplitude decay for all the frequencies analyzed, the regions of Lombardia and Eastern Sicily show the smallest attenuation. The Marche region also shows a strong amplitude decay, particularly for frequencies f > 3 Hz, and in the frequency band between 1 and 3 Hz the rate of decay of the spectral amplitudes with distance becomes similar to that of the region of Friuli. Since the attenuation functions analyzed represent different geologic and tectonic environments, we used them to calculate an average set of attenuation functions, one per frequency, for the hypocentral distance range between 10 and 120 km. The resulting functions permit a mean attenuation correction to spectral records of S waves in regions of Italy where the specific values of the attenuation parameters are unknown