Empirical ground-motion prediction equations for Northem Italy using weak- and strong-motion amplitudes, frequency content, and duration parameters

The goals of this work are to review the Northern-Italy ground-motionprediction equations (GMPEs) for amplitude parameters and to propose new GMPEsfor frequency content and duration parameters. Approximately 10,000 weak andstrong waveforms have been collected merging information from different neighboringregional seismic networks operating in the last 30 yr throughout Northern Italy.New ground-motion models, calibrated for epicentral distances ≤100 km and for bothlocal (ML) and moment magnitude (Mw), have been developed starting from a highquality dataset (624 waveforms) that consists of 82 selected earthquakes with ML andMw up to 6.3 and 6.5, respectively. The vertical component and the maximum of thetwo horizontal components of motion have been considered, for both acceleration(peak ground horizontal acceleration [PGHA] and peak ground vertical acceleration[PGVA]) and velocity (peak ground horizontal velocity [PGHV] and peak ground verticalvelocity [PGVV]) data. In order to make comparisons with the most commonlyused prediction equations for the Italian territory (Sabetta and Pugliese, 1996 [hereafter,SP96] and Ambraseys et al. 2005a,b [hereafter, AM05]) the coefficients for accelerationresponse spectra (spectral horizontal acceleration [SHA] and spectralvertical acceleration [SVA]) and for pseudovelocity response spectra (pseudospectralhorizontal velocity [PSHV] and pseudospectral vertical velocity [PSVV]) have beencalculated for 12 periods ranging between 0.04 and 2 sec and for 14 periods rangingbetween 0.04 and 4 sec, respectively. Finally, empirical relations for Arias intensities(IA), Housner intensities (IH), and strong motion duration (DV) have also been calibrated.The site classification based on Eurocode (hereafter, EC8) classes has beenused (ENV, 1998, 2002). The coefficients of the models have been determined usingfunctional forms with an independent magnitude decay rate and applying the randomeffects model (Abrahamson and Youngs, 1992; Joyner and Boore, 1993) that allow thedetermination of the interevent, interstation, and record-to-record components of variance.The goodness of fit between observed and predicted values has been evaluatedusing the maximum likelihood approach as in Spudich et al. (1999). Comparingthe proposed GMPEs with SP96 and AM05, it is possible to observe a faster decay ofpredicted ground motion, in particular for distances greater than 25 km and magnitudeshigher than 5.0. The result is an improvement in fit of about one order of size formagnitudes spanning from 3.5 to 4.5.