ATTENUATION RELATIONS OF HORIZONTAL AND VERTICAL GROUND MOTIONS FOR INTRASLAB AND INTERPLATE EARTHQUAKES IN JAPAN

Abstract

Vertical motions have been required as input motions to important structures, such as nuclear power plants and base-isolation structures. However, empirical attenuation relations of vertical motions for big intraslab and interplate earthquakes in Japan had not been proposed yet. Therefore in this study we develop attenuation relations for estimating horizontal and vertical ground motions caused by these earthquakes. The relations are provided for peak ground acceleration (PGA), peak ground velocity, and 5% damped acceleration response spectrum (SA) for radial, transverse, and vertical components. In order to use the relations as input motions we obtain site coefficients at bedrock with different S-wave velocities. The attenuations of horizontal motions in this study obtained from records observed at the fore-arc are smaller than those in the previous ones. The ground motions for big intraslab and interplate earthquakes occurring at the Pacific plate are larger than those at the Philippine Sea plate at most cases. We find that the PGA and the SA in a short period range for intraslab earthquake are larger than those for interplate earthquakes at the same focal depth D and are roughly proportional to D2/3.