A SITE-DEPENDENT SEISMIC HAZARD MAPFOR THE FRIULI - VENEZIA GIULIA REGION (NE ITALY)

摘要

The local site conditions strongly influence the seismic hazard of a region, but, traditionally,regional seismic hazard studies refer to rock or to a reference rigid soil. Nowadays, GISapplications allow the handling of local hazard variations from a regional to a local scale. Wepresent seismic hazard maps for the Friuli - Venezia Giulia Region (NE Italy) that take intoaccount the different soil conditions. The soils have been mapped on a geological-lithologicalbasis. In the Friulian Plain, over 1,000 borehole stratigraphies, and extensive geophysicalsurveys, were used to infer the geometrical and mechanical properties of the Quaternarydeposits, and to find the depth of the pre-Quaternary substratum. Firstly, seismic hazard wascomputed for outcropping hard rock as well as soft soil, taking into account a standardprobabilistic approach and European empirical attenuation relations. Secondly, amonodimensional modelling was performed to simulate the local responses. For this, thewhole Quaternary overburden was modelled by 1-D simplified linear models considering twotypes of bedrock, six intervals of seismic impedance, and five depth intervals. The final mapsclearly indicate the influence of the site effects both within the mountain area and the plain,where the variations of the regional seismic responses are conditioned by some abruptchanges of the depth of the Quaternary overburden. GIS applications allow us to take localamplifications more properly into account even at the regional scale of this study.