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Abstract:
The paper investigates the seismic response of highly populated, or economically important areas for a wide range of magnitudes. Intermediate-depth earthquakes occurring in Vrancea, Romania, are the most hazardous seismic source at national scale, affecting large parts of the country territory.
The sites are representatively chosen for their different local soil conditions given by the specific rocks content, layering and impedance contrast in the shear waves velocity. The response at each site is investigated through spectral composition by comparing the processed elastic response spectra of strong earthquakes to those of medium or smaller magnitude. For this reason pairs of collocated (depth, hypocentral distance) stronger-lower magnitude are chosen, in order to minimize the effect of propagation path. The local amplification in correspondence to the site characteristics is highlighted and spectral ratios for each of the pairs of elastic response spectra were performed, in order to correlate the specific site’s behavior to the local effects as influenced by the seismic source strength.
The influence of local conditions is enhanced by the increase in magnitude, as higher magnitudes probably set in motion thicker package layers, and an increase in the soil predominant period values may be encountered. For some other areas the oscillating period corresponding to the peak spectral amplitude is rather stable, hence the local site conditions are primarily controlling this behavior. The stabilization tendency for the spectral content offers the possibility to predict the characteristic values even for the future strong seismic events in these areas.
Work financed by Nucleu PN2336 SOL4RISC
