Comparison of asynchronous signals generated from surface or bedrock natural accelerograms.

The non-synchronism of the seismic action is particularly important in the case of structures with considerable longitudinal extension. The propagation of motion in the soil is influenced by factors such as different types of foundation soils and heterogeneity of stratigraphic profiles, which determine a variation of the amplitudes and frequencies of the signals at different points in space. The objective of this work is the generation of a sample of asynchronous signals at different points in space, starting from natural accelerograms related to a given seismic event. These signals are inputs for successive linear and nonlinear seismic analyses. In this study we have implemented the computer code GAS (Nuti and Vanzi, 2005). The original GAS code generated earthquake samples of a random field matching given response spectra. Now the code starts from real accelerograms. The code has been applied and calibrated using for the same sites different generation procedure: a) propagation at the free field, b) propagation at the bedrock and subsequent local amplification. The procedure has been applied to real cases for which records in different points of the free field are known. The code EERA (J.P. Bardet, et al., 2000) has been used for soil amplification and deconvolution