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Free keywords:
Fourier analysis; Earthquake ground motions; Seismic attenuation; Site effects
Abstract:
We process a large number ofseismic recordings in Europe (i.e. about halfa million recordings from about 19 500 earthquakes) with the aim of decomposing the Fourier amplitude spectra into source, propagation and site effects. To account for first-order, large-scale regional differences in propagation effects, the spectral decomposition simultaneously solves six different models describing the spectral attenuation within different subregions. Since the decomposition approach is affected by trade-offs that make the solution non-unique, we assume a station installed on rock in Switzerland as reference station and we invert for relative site amplifications. To propagate the reference site condition to the entire data set, we develop a procedure based on a sequence ofdecompositions considering increasing and overlapping data sets. The applied procedure allows for a consistent evaluation of relative site effects for about 3200 station channels using a single reference station for the whole data set. Comparisons with site amplifications obtained in previous studies at common stations in Italy and Switzerland confirm the site amplification results. The target ofthis work is to show that the spectral models obtained for attenuation and site effects can be used to generate empirical shaking scenarios in the Fourier domain. Therefore, we conclude our feasibility study by presenting shaking maps generated at different frequencies for hypothetical magnitude 6.5 earthquakes with a Brune-type stress drop of 10 MPa located at different positions across Europe.
