One-dimensional geotechnical modelling by seismic methods of Lisbon alluvial basins

Abstract

An experimental seismic microzonation was executed in Lisbon, in 1991, In this paper the results obtained in alluvial basins are compared, by spectral analysis, with those from one-dimensional (1D) nonlinear models. Geotechnical parameters are estimated for some sites in each basin, such as layer thickness, soil type (clay, sand or rock), mass density and shear wave velocity. SHAKE program, with 1969/2/28 Lisbon's earthquake accelerogram, was used to optimize theoretic models. Average relationships between dynamic shear modutus and damping ratios of soils, as functions of shear strain, were considered. With this analysis it was possible to verify the existence of great soil amplifications at low frequencies depending on alluvium thickness at each site.