Abstract
Microtremor array measurements have been carried out to estimate the detailed S-wave velocity structures of shallow soil structures in the Tachikawa-fault zone. Array measurements of vertical microtremors were used to retrieve phase velocity of Rayleigh wave. Through the inversion of the phase velocities, we have estimated the S-wave velocity structures. The shallow S-wave velocity structures have significant variation in the vicinity of the northern part of Tachikawa-fault. Depths to the engineering bedrock in the southwest part of the fault are deeper than those of the northeastern part of the fault. The southern part of the fault zone exhibits a complex variety in the S-wave velocity structures, with the variety of amplification in the area. The AVS30 has the significant relationship with amplification such that high AVS30 makes small amplification and short dominant period. The variety of the structure expected from existing information was also found in the S-wave velocity structures estimated in this study. However, AVS30 in this study was relatively higher than that from the geomorphological classification. It generates the amplification smaller in this study and shortens the dominant period than that estimated from geomorphological classification. However, since this characteristic can be held only in Tachikawa-fault zone, it is important to predict the strong motion characteristics based on the precise investigation of the S-wave velocity in the target area.
