Q-values and velocities for S-waves propagating in sedimentary layers on the basement are evaluated from spectral ratios strong motion records through an optimal analysis. The strong motion records are obtained by 4 borehole array observations with the depths from 100 to 950 m in Southern Tohoku and Kanto districts in Japan, and available frequencies for the analysis range from 0.5 to 20 Hz. The velocity V_s structures obtained in the present study are consistent with the results by the PS-logging at all the stations. The Q-values are increase with frequency f in proportion to f^<0.2-1.0> between 0.5 to 10 Hz.
