GNGTS 2013 - Atti del 32° Convegno Nazionale

coming from 1980 horizontal component seismograms. The functional form used to derive the GMPEs is a simplified version of the model adopted by Boore and Atkinson (2008). In particular, we did not consider the term depending on the style of faulting, since this kind of information is available for few of events. Moreover, Boore and Atkinson (2008) introduced the hinge magnitude ( M h ) at which the shape of magnitude scaling changes from a quadratic form (low magnitude events) to the linear form (high magnitude events). Since the range of magnitudes we investigated includes only low M L values, we omitted it from our equation for predicting ground motion. from our equation for predicting ground motion. Consequently, our magnitude scaling is quadratic. The last difference concerns the site amplification that Boore and Atkinson (2008) puts equal to the sum of a linear and a nonlinear terms. For the identification of the coefficients we applied the Marquardt-Levenberg technique, which allows the estimation of non-linear parameters in the model, in particular the pseudo- depth h. Various configurations were tested, both with respect to distance intervals as well as the role of soil conditions. Given the peculiar conditions of the shallow Mount Etna events, we suggest the use of a law based on records obtained at less than 15 km for estimating ground motion to the epicenter. At the same time the role of soil type remains unclear – at least as long as classification is based on generic information rather than on-site investigations of the geotechnical properties encountered at a seismic station. Given the lack of that information we propose to use the laws obtained for the most commonly met conditions (i. e., soil class “B”). Corrections for sites belonging to other soil classes may be applied following the rules given the seismic codes (e. g., EC8). As a caveat we underscore that estimated peak ground accelerations become highly instable when extrapolating the relations to magnitudes and distances not covered by the observations. References Albarello D., Bosi V., Bramerini F., Lucantoni A., Naso G., Peruzza L., Rebez A., Sabetta F. and Slejko D.; 2000: Carte di pericolosità sismica del territorio nazionale . Quad. di Geofis. 12, ING, Roma, 7 pp., CD-Rom, 4 annexes (in Italian). Azzaro R.; 2004: Seismicity and active tectonics in the Etna region: constraints for a seismotectonic model . In: Bonaccorso A., Calvari S., Coltelli M., Del Negro C. and Falsaperla S. (eds.), Mt. Etna: Volcano Laboratory, AGU Monograph, 143 pp. 205–220. Azzaro R., D’Amico S., Mostaccio A., Scarfì L. and Tuvè T.; 2006: Terremoti con effetti macrosismici in Sicilia orientale nel periodo gennaio 2002-dicembre 2005 . Quad. Geofis., 41 , INGV, Roma (in Italian). Boore, D.M. and Atkinson G.M.; 2008: Ground-motion prediction equation for the average horizontal component of PGA, PGV, and 5%-damped PSA at spectral Periods between 0.01 s and 10.0s . Earthquake Spectra, 24 , 99-138. Fig. 3 – Observed PGA values (diamonds), compared with respect to the GMPEs obtained in this study (continuous lines) for epicentral distances less than 30 km (red line) and 15 km (blue line), respectively, for M L = 3.0 (a) and 4.0 (b). 157 GNGTS 2013 S essione 2.1