Q AND SITE AMPLIFICATION FACTORS OF HARD-ROCK REGION IN THE KITAKAMI MASSIF, NORTHEASTERN JAPAN

We observed three explosions along a 60 km profile in the central part of the Kitakami massif, northeastern Honshu, Japan. Explosion sites a nd most of the observation sites were located on hard-rock outcrops. U sing P-wave first arrivals, the average Q(P) along ray paths and site amplification factors were determined for the frequency range between 6 and 30 Hz based on the amplitude spectra decay with distance. Q(P) i ncreased proportional to f(n) (n is approximately equal to 0.9). The d ifference in amplification factors among hard-rock sites was as much a s a factor of five for frequencies lower than 12 Hz and became large a t higher frequencies, Q(S) and S-wave site amplification factors were obtained only for 5 and 7.5 Hz. Q(S) was slightly larger than Q(P), bu t the difference was not significant. S-wave site amplification factor s were more variable than those of P-wave among the stations.