Q and site amplification factors of hard-rock region in the Kitakami Massif, northeastern Japan

We observed three explosions along a 60km profile in the central part of the Kitakami massif, northeastern Honshu, Japan. Explosion sites and most of the observation sites were located on hard-rock outcrops. Using 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 increased proportional to fⁿ(n=0.9). The difference in amplification factors among hard-rock sites was as much as a factor of five for frequencies lower than 12 Hz and became large at 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, but the difference was not significant. S-wave site amplification factors were more variable than those of P-wave among the stations.