Empirical ground motion prediction equations for northern italy using weak and strong motion amplitudes, frequency content and duration parameters

The aims of this work are to review the Northern-Italy ground motion prediction equations (hereinafter GMPEs) for amplitude parameters and to propose new GMPEs for frequency content and duration parameters. Approximately 10.000 weak and strong waveforms have been collected merging information from different neighbouring regional seismic networks operating in the last 30 years throughout Northern Italy. New ground motion models, calibrated for epicentral distances ≤ 100 km and for both local (Ml) and moment magnitude (Mw), have been developed starting from a high quality dataset (624 waveforms) which consists of 82 selected earthquakes with Ml and Mw up to 6.3 and 6.5 respectively. The vertical component and the maximum of the two horizontal components of motion have been considered, for both acceleration (PGHA and PGVA) and velocity (PGHV and PGVV) data. In order to make comparisons with the most commonly used prediction equations for the Italian territory (Sabetta and Pugliese, 1996 and Ambraseys et al. 2005a,b hereinafter named SP96 and AM05) the coefficients for acceleration response spectra (SHA and SVA) and for pseudo velocity response spectra (PSHV and PSVV) have been calculated for 12 periods ranging between 0.04 s and 2 s and for 14 periods ranging between 0.04 s and 4 s respectively. Finally, empirical relations for Arias and Housner Intensities (IA, IH) and strong motion duration (DV) have also been calibrated. The site classification based on Eurocode (hereinafter EC8) classes has been used (ENV, 1998). The coefficients of the models have been determined using functional forms with an independent magnitude decay rate and applying the random effects model (Abrahamson and Youngs, 1992; Joyner and Boore, 1993) that allow the determination of the inter-event, inter-station and record-to-record components of variance. The goodness of fit between observed and predicted values has been evaluated using the maximum likelihood approach as in Spudich et al. (1999). Comparing the proposed GMPEs both with SP96 and AM05 it is possible to observe a faster decay of predicted ground motion, in particular for distances greater than 25 km and magnitudes higher than 5.0. The result is a fit improvement of about one order of size for magnitudes spanning from 3.5 to 4.5.In press4.1. Metodologie sismologiche per l'ingegneria sismicaJCR Journalope