A new/modified technique for the separation of source, path and site effects from strong motion records is proposed. To do this we made two extensions of the method developed in [Iwata and Irikura, 1988>. (1) We allow the Q-value to be variable with depth and subregion in a block model of the medium with constant Q in each block. Path lengths within blocks are calculated using ray approximation. (2) To estimate the absolute site effect at reference station (and source effects respectively) we can use the H/V spectral ratio method for the S-wave group to determine the spectral correction at the reference station. Our new method was applied to a set of KNET data in the Tohoku area of Japan. Preliminary results of Q structure inversion show that Q has minor variations with depth, and slightly decreases in the deepest layer. Source effects clearly show the existence of fmax phenomena (fmax=13 Hz). ¿ 2000 American Geophysical Union