Numerical simulation of site effects versus the Nakamura's technique: the case of Almeria city

Abstract

The estimation of seismic motion, during an earthquake, is an important goal to mitigate the seismic damage. This estimation is sometimes difficult to perform when there are also soft surface soils which can produce great amplifications in the amplitudes of the motion, non-linear effects, and large durations in the signals. When there are not enough records of earthquakes in a given place it is possible to compute the characteristics of site effects using numeri cal methods; using this kind of techniques it is possible to understand the seismic response of soft basins in both, time and frequency domains. In this work we use the data (velocities, densities, depths, etc.) obtained from bore hole experiments and seismic refraction surveys to compute the seismic response of Ciudad Jardin (Almeria), with the Thompson-Haskell method. This zone, classified as soft soil, has been studied as part of a comprehensive research project on seismic vulnerability assessment in Almeria city, in which the Nakamura' s technique was applied to obtain the predominant period of the soil. We compare the numerical results, using a 1D model, in the frequency domain with those obtained with the Nakamura's technique at this part of Almeria city; in this work we show the parts of the spectra that are in agreement and those that are no coherent on this type of soil.