Strong ground motion simulation in the urban area of Catania on the basis of a detailed geological survey

Abstract

Catania is one of the cities with major seismic hazard in Italy. In history the city was repeatedly hit by destructive earthquakes, e.g., the events of 1 169, 1542 and 1693, all with estimated magnitudes around or above 7. The purpose of our research is the study of site effects and response of soil in the Catania urban area based on synthetic simulations. We have considered three scenarios with earthquakes whose magnitudes range from 5.5 to 7.0 and whose epicentral distances are supposed to be in the range 12-35 km. The subsurface geology of the urban area of Catania is characterized by a marlyclay substratum overlain by lavas, sands and conglomerates. The lava thickness range from a few to over 60 meters, while the thickness of sand terraces ranges from a few to 30 meters. Our study is based on ca. 100 boreholes from which geotechnical and geophysical data were available. We calculated synthetic accelerograms and response spectra at all borehole sites. The results highlight the importance of the subsurface geological conditions, in particular the presence of low velocity layers which enhance seismic loading. On the other hand thick lava layers act as protecting shields against earthquake shaking. Transactions on the Built Environment vol 38 © 1999 WIT Press, www.witpress.com, ISSN 1743-3509