Earthquake design response spectra for nuclear installations in Switzerland

A statistical evaluation of strong motion records typical for the seismotectonic conditions existing in Switzerland was made to develop guidelines for establishing and reviewing earthquake design spectra for nuclear installations in Switzerland. Selection criteria, such as focal parameters of the earthquake, distance from epicenter to recording station, local conditions at recording station, and quality of the strong motion data were determined to select a final data set of 19 records on rock and 22 records on stiff alluvium out of more than 200 records predominantly from Southern Europe. A statistical analysis of these data was made to determine the 84 percentile piecewise linear design response spectra. The comparison with the horizontal US NRC spectra showed a considerable reduction in response for frequencies lower than 3.5 Hz for rock sites and 2.5 Hz for soil sites. The vertical design spectra could be established as 2/3 of the corresponding horizontal spectra over the entire frequency range. (orig.)