Evaluation of Earthquake Response Spectra Considering Depth of Seismic Bedrock

Abstract eng:
The design earthquake motions are often defined by the response spectra. For example, in the seismic design standard for the Japanese Railway facilities (1999) there are two types of design spectra for the Level-1 earthquake and the Level-2 earthquake. The Level-1 earthquake is the earthquake, which has an occurrence probability of a few times during the service life of the structures. The Level-2 earthquake motions have high intensity, which are defined by taking into account earthquake activities in the inter-plate regions (Spectrum-I) and defined by considering the near source earthquake motions characteristics caused by intra-plate earthquakes (Spectrum-II). The Spectrum-II for the Level-2 earthquake has been evaluated by chiefly using the records observed in the 1995 Hyogo-ken Nambu earthquake. These records have been observed at the site where the strong motions were largely amplified due to the influence of the deep seismic bedrock. However, the ground motions were not so much amplified at the site with the shallow bedrock. Therefore, we propose the response spectra for the Level-2 earthquake considering the depth of the seismic bedrock. In the area with shallow bedrock, we can make the designed spectra approximately 30 percent less than those in the deep area at the longer period. Using these proposed spectra, the seismic design become more rational for the structures built in mountain areas with shallow bedrock.

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