Behavior of Horizontal and Vertical SV at JMA Sites, Japan

Abstract

Characteristics of response spectra of free-field horizontal and vertical ground motion recorded by JMA-87 type accelerometers are examined. The database includes 2,166 response spectra of motions from 387 events recorded at 76 JMA sites (70% on hard soil or rock and 30% on medium to soft soil). Most of the ground motions are far-source records. Relative spectral velocities at 0, 2, and 5% critical damping for 22 periods in the range of engineering interest have been subjected to nonlinear regression procedures in terms of magnitude and hypocentral distance. The attenuation relations consider the effect of depth and the local site amplification. A numerical technique called iterative partial regression is used to apply Joyner and Boore's two-stage regression methodology while considering the effect of the recording site. Dependence of horizontal and vertical response spectra, and their ratio, on magnitude, site-to-source distance, and depth are investigated through the development of attenuation relationships for horizontal and vertical spectral ordinates. The horizontal-to-vertical (H/V) response spectral ratio is found to be strongly dependent on period. At short periods, the value of the H/V spectral ratio is 1.5, but with an increase in period from an intermediate to a longer range, the spectral ratio attains a value of 3. These characteristics of H/V spectral ratio are likely to be universal for far-source recordings. The frequency-dependent relative amplification of the sites are found to be distinctive from site to site, and it is found that stations with the same soil type classification show an apparent pattern. Because the local site characteristics are explicitly derived, the resulting predictive equations can be considered as site-specific response spectra for the 76 JMA stations examined here.