Evaluation of site coefficients for aseismic building design: seismological and geotechnical investigations in two historical centres of the Marche region, Italy.

Abstract:Great research effort has been directed over the last 30 years into quantification of site responses during earthquakes. In Italy, most of this work was motivated by the need to carry out major engineering projects (nuclear plants, towers, bridges, etc.). Recently, after the last seismic events of September- October 1997 that affected one of the most important historical zones of Central Italy, some regional governments promoted extensive systematic ground response and microzonation studies in a few test sites in the Emilia-Romagna, Marche, Umbria and Toscana regions with the objective of providing new updated guidelines for building design in these regions. Although the seismicity in Central Italy is generally moderate and the maximum expected magnitudes are about 6-6.5, many urban settlements and villages experienced very severe damage even during low magnitude earthquakes, that can be attributed to the sharp topography or to the deep thickness of deposits or the dynamic properties of soils. By means of multidisciplinary investigations, including geotechnical dynamic field and laboratory testing, and analytical studies, the exposition of these territories to the expected earthquakes and the coefficients for evaluating seismic actions for building design have been determined. This paper describes how ground responses were evaluated in two test historical centres of the Marche region, and the criteria followed for assigning the site coefficients for seismic building design to the zones exhibiting different seismic responses.