Improving the Italian strong ground motion attenuation relationship: preliminary results with an updated accelerometric data set

摘要

Strong ground motion attenuation relationships are fundamental tools for seismic hazardevaluation. In Italy the most widely used attenuation relationship is the Sabetta andPugliese (1987 and 1996, here afters referred to as SP96) for evaluating peak groundacceleration, peak ground velocity, Arias intensity and pseudovelocity response spectra,of the Italian territory. The equation has been derived using 95 records relative to17 earthquakes with magnitude ranging from 4.6 to 6.8. The SP96 relation is basedon the strongest events since the installation of accelerometric instruments in Italy,dated 1972, such as Friuli 1976, Valnerina 1979, Irpinia 1980, and Lazio-Abruzzo1984, which is the most recent event. In the time span 1984 – 2007 other moderateseismic events occurred in Italy, namely the East Sicily 1991, Umbria-Marche 1997-1998, Pollino 1998 and Molise 2002, with moment magnitude > 5, and huge datasets have been obtained due to the installation of many temporary stations and digitalinstruments. The Umbria-Marche and Molise accelerometric data sets allowed the calculationof regional attenuation relationships that show a considerably different trendcompared to the SP96. In this time span a project for an updated Italian accelerometricdata base construction has been started with the aim of collecting all the accelerationtime histories recorded since 1972 and re-evaluating, updating and improving eventparameters, data processing and station geological/geotechnical characteristics.The aim of this research is the implementation of a new weighted regression analysis with the expanded and updated database, including coefficients to model themagnitude-dependent decay rate, the faulting mechanism, the local site effects andthe magnitude-dependent variance. In addition, the fit of the SP96 equation to the newaccelerometric data set spanning from 1972 to 2004 is evaluated with the aid of differentstatistic techniques, in order to verify the need of deriving a new attenuationequation.