Applying microtremor, gravity anomalies and numerical modelling methods for the evaluation of soil earthquake response in Barcelona, Spain

Two different techniques have been applied to evaluate the potential seismic site effects in the city of Barcelona. Transfer functions have been computed in different sites, through a unidimensional linear-equivalent model using the available dynamic parameters of soils obtained from drillings for building and infrastructure public works. The depth of the basement and the structural framework have been determined from the inverse solution of the residual gravity anomaly. Microtremor measurements using Nakamura's technique are also available for these sites. The results of these techniques have been compared. We prove that the predominant frequencies obtained by Nakamura's technique agree with the fundamental frequencies in the computed transfer functions, but for complex structures these fundamental frequencies are not the frequencies for which largest amplifications appear. In our case, the fundamental frequency is related with the post-Palaeozoic deposit thickness, which is defined by the results from inversion of a detailed gravity survey, while the maximum amplification depends more on the uppermost soft soils.