Site amplification factors are evaluated for strong-motion sites in Japan by using spectral inversion technique. A new criteria is introduced to deterrmine the reference site, where site amplification factor is assumed to be unity. The analysis is conducted for six regions in Japan, namely, Kyushu, Chu-goku-Shikoku, Kinki, Chubu, Kanto and Tohoku-Hokkaido regions.
　Site amplification factors are evaluated for strong-motion sites all over Japan including K-NET sites, KiK-net sites and sites at major ports. The seimic moment calculated from the source spectra, which is obtained through the analysis, agrees well with that of the CMT solution of the F-net, indicat-ing the validity of the criteria to determine the reference site. For several sites, where large site amplifi-cation facrors are obtained, strong motion simulations are conducted to validate the amplification fac-tors.
　The amplification factors thus obtained can be used to evaluate strong' ground motions from future large earthquakes in conjunction with the stochastic Green's function method. The source spectra and the site amplification factors obtained in this study are available on the attached CD.