2007 Volume 57 Issue 9-10 Pages 309-325
Microtremor array measurements (MAM) have been applied to delineate buried incisedchannels in urban area of Japan. The site is a rectangular of 6 km ×4 km in the Nakagawa Lowland placed at Soka and Misato cities in Saitama prefecture, Japan. One-hundred and four MAM have been carried out to delineate buried incised-channels filled with unconsolidated alluvial deposits (Chusekiso) thicken about 50 m. Triangle arrays were used at wide area, such as parks. L shaped arrays using roads and crossings were also used for the data acquisition at the most of the site. A spatial auto correlation (SPAC) method was applied to the approximately 10 minutes vertical component of microtremor data. Phase-velocity curves were calculated in the frequency range of between 2 and 10Hz. In spite of cultural noise or irregular array shape, fundamental mode of phase-velocity curves are clearly obtained in the all observed points. An one-dimensional inversion using a non-linear least square method has been applied to the phase-velocity curves to obtain one-dimensional S-wave velocity structures. These one-dimensional structures were interpolated into a three-dimensional structure. We succeeded to map the shape and the depths of buried channel that agree with the borehole data very well. The reconstructed shape and the depths of buried incised-channel fit well with those interpreted from borehole data.
