BEHAVIOR OF HORIZONTAL AND VERTICAL SV AT JMA SITES, JAPAN

Characteristics of response spectra of free-field horizontal and verti cal ground motion recorded by JMA-87 type accelerometers are examined. The database includes 2,166 response spectra of motions from 387 even ts recorded at 76 JMA sites (70% on hard soil or rock and 30% on mediu m to soft soil). Most of the ground motions are far-source records. Re lative spectral velocities at 0, 2, and 5% critical damping for 22 per iods in the range of engineering interest have been subjected to nonli near regression procedures in terms of magnitude and hypocentral dista nce. The attenuation relations consider the effect of depth and the lo cal site amplification. A numerical technique called iterative partial regression is used to apply Joyner and Boore's two-stage regression m ethodology while considering the effect of the recording site. Depende nce of horizontal and vertical response spectra, and their ratio, on m agnitude, site-to-source distance, and depth are investigated through the development of attenuation relationships for horizontal and vertic al spectral ordinates. The horizontal-to-vertical (H/V) response spect ral ratio is found to be strongly dependent on period. At short period s, 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 att ains a value of 3. These characteristics of H/V spectral ratio are lik ely 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 cl assification show an apparent pattern. Because the local site characte ristics are explicitly derived, the resulting predictive equations can be considered as site-specific response spectra for the 76 JMA statio ns examined here.