Response Spectra for Design Purpose of Stiff Structures on Rock Sites

摘要

Based on analyses of earthquake ground motion records on rock, we propose an empirical method for evaluatingresponse spectra and time-dependent features of horizontal and vertical earthquake ground motions on free rock surfaces.This method is aimed at aseismic design of nuclear power facilities. A response spectrum of horizontal earthquake groundmotion on seismic bedrock is given by a control point in the matrix formed by four magnitudes M = 6.0, 7.0, 8.0, and 8.5;and four equivalent hypocentral distances X_(eq) defined as very near, near, intermediate, and far. The response spectra for other M and X_(eq) e are determined by interpolation between values in the matrix. The response spectra of the horizontal and vertical ground motions on the free rock surface are determined by multiplying the horizontal motion on the seismicbedrock by the amplifications of horizontal and vertical motions due to surface layers. The amplifications by the surfacelayers are given as a function of S-wave velocities V s from 0.5 to 2.7 km/s for horizontal components and as a function ofP-wave velocities V_p from 1.7 to 5.5 km/s for vertical components on the free rock surface. The time-dependent envelopeand the correction coefficient of the response spectrum due to a damping factor are given as functions of M and X_(eq).Examination of the evaluation equation's applicability using observations from inside and outside Japan show that theevaluation method can adequately explain both the observation records of large earthquakes and of near-source regions.