We present a set of ground motion prediction equations (GMPEs) derived for the geometrical mean of the horizontal components and the vertical, considering the latest release of the strong motion database for Italy. The regressions are performed over the magnitude range 4 -6.9 and considering distances up to 200 km. The equations are derived for peak ground acceleration (PGA), peak ground velocity (PGV) and 5%-damped spectral acceleration at periods between 0.04 and 2 s. The total standard deviation (sigma) varies between 0.34 and 0.38 log 10 unit, confirming the large variability of ground shaking parameters when regional data sets containing small to moderate magnitude events (M < 6) are used. The between-stations variability provides the largest values for periods shorter than 0.2 s while, for longer periods, the between-events and between-stations distributions of error provide similar contribution to the total variability.

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The selection of specific elastic response spectra according to soil categories is the easiest way to account for site effects in engineering projects and general-purpose hazard maps. Most of the international seismic codes make use of the average shear wave velocity of the upper 30 m (Vs ,30 ) to discriminate soil categories, although some doubts arose about the capability of Vs ,30 to predict actual soil amplification. In this work we propose two soil classifications in which the soil fundamental frequency (f 0 ) becomes either an alternative or a complement to Vs ,30 . The performance of the derived categorizations is achieved through the estimation of the standard deviation associated to ground motion prediction equations of acceleration response spectra, considering recordings extracted from the Italian strong motion data base. The results indicate that there is a significant reduction of the standard deviation when the classification is based on the couple of variables Vs ,30 -f 0 , although a classification based of the single f 0 also leads to satisfactory results, comparable with those obtained assuming a classification scheme based on Vs ,30 .

[1] We apply a nonparametric spectral inversion scheme to calculate source spectra, S wave attenuation, and site transfer functions from strong motion records in the epicentral region of the 1997-1998 Umbria-Marche seismic sequence (central Italy). We use records from moderate size earthquakes (4.6 M l 5.9) to parameterize the spectral amplitude decay in the distance range from 5 to 40 km. We find that the average quality factor Q can be approximated by Q( f ) = 49 f 0.9 , between 0.5 and 8 Hz, and the geometrical spreading by r À0.9 . At high frequencies ( f > 8 Hz) the dependence of Q on frequency weakens, and it takes an approximate constant value of 318. We fit the source spectra to the w-square model and calculate an average stress drop of (2 ± 1) MPa. The average value is consistent with the previous estimates from the weak events (1.4 < M l < 4.5) of the Umbria-Marche seismic sequence. The most remarkable site effects are found in correspondence of large sedimentary basins, filled by alternation of sandy-clayey deposits. The estimated spectral parameters are used to simulate acceleration spectra recorded during several earthquakes of the Umbria-Marche sequence. Both point source and finite fault effects are considered. Furthermore, attenuation relationships for peak ground velocity and ground acceleration are estimated using synthetic data, and compared to existing relationships.