The Katsuyama basin is located along the middle strecth of the Kuzuryu River, where fluvial terraces and fans have developed. We estimated the subsurface structure of the basin based on microtremor observation data. The H/V spectrum ratios were calculated from the single point measurement data. The peak periods and corresponding amplitudes were extracted and their distributions among the segments of the terraces and fans were investigated. In the array observations, the distance between center seismometer and each one was deployed geometric progression like. Thus, the Rayleigh wave phase velocities could be determined efficiently by using the extended SPAC method. By using a genetic algorithm, the phase velocity and the H/V ratio of each observation point were inverted to a vertical S-wave velocity profile. Connecting several inverted profiles, subsurface cross-sections of the Katsuyama Basin were evaluated.