Computation of the strong motions during the 1995 Hyogo-ken Nanbu earthquake, combining the k-square spectral source model and the discrete wavenumber technique.

C. Berge-Thierry, P. Lussou, B. Hernandez, F. Cotton and J.C Gariel
Institut de Protection et de Sûreté Nucléaire, Fontenay-aux-Roses, France

Abstract. We compute the strong ground motion at the 6 sites located in the Kobe Basin (KBU, KB1-4, RKI stations), using a stochastic spectral source description (Bernard et al., 1996), and the discrete wavenumber technique (Bouchon & Aki, 1977) in order to calculate complete field Green's functions in a 1D medium. Such a model enables the generation of realistic (in temporal and spectral domains) broad-band strong motions. It is a numerical extended fault model. The rupture complexity is described by a specific seismic slip distribution, which has a k -2 spectral decay (k being the radial wavenumber). A rupture pulse propagates on the fault with a constant velocity, installing the dislocation. This model generates the standard frequencial w 2 radiation for the accelerograms, as observed on the 1995 Kobe records, and allows to account for the directivity properties of the sources. The horizontal strong motion for the stations located in the basin is obtained by the convolution between the accelerogram evaluated at depth using the model described above and the non-linear transfer-function of the surrounding sediments (computed by a non-linear code called CyberQuake). The frequency validity domain of our synthetics is 0.1 to 4 Hz.