Characteristics of seismic motions on rock sites through highly accurate strong-motion earthquake observation network

Observed accelerograms are analyzed through the regression analysis to elucidate the differences of seismic-wave amplifications by the ground of hard-rock site (Vs=1.4 km/s) and soft-rock site (Vs=0.7 km/s). Vs is shear wave velocity. Obtained results are summarized as follows: 1) Peak accelerations in both horizontal and vertical components at hard-rock site are about 0.5 to 0.6 times smaller than the soft-rock site. 2) Horizontal peak accelerations are about 1.2 to 1.5 times of vertical ones at soft-rock site and about 1.1 to 1.4 times at hard-rock site for earthquakes with magnitude from 4 to 6. 3) Response spectra at the hard-rock site are about 0.4 to 0.6 times of those at the soft-rock site in the period range shorter than 0.2 second. This is approximately consistent with the result of peak accelerations. 4) Amount of long period components of response spectra relatively increases with earthquake magnitude. Hypocentral distance little affects the rate of frequency components of response spectrum, comparing with magnitude in the range of hypocentral distance shorter than 150 km. (orig./HP)