Delineation of Detailed Structure in Holocene Unconsolidated Sediments using S-wave Type Land Streamer

High-resolution shallow seismic reflection surveying using SH-wave type Land Streamer was conducted in the Tokyo Metropolitan area, where more than 25 million inhabitants concentrate in small but highly developed region of 3,500 square km. While seismic reflection surveys have been frequently conducted in the area to delineate relatively deep geologic structure as concealed active fault surveys, shallow reflection surveys have been exceptional due to the difficulty in surveying at such a high land-use area disturbed by high amplitude traffic and industrial noises. In contrast, the Land Streamer makes it easy to set a survey line and acquire high quality data even in urban area owing to its short array length along with appropriate coupling with paved surface through a metallic baseplate. We adopted it for the field surveys conducted in the Tokyo Metropolitan area to clarify the detailed structure in a buried valley filled with Holocene unconsolidated soft sediments, and to characterize them based on the S-wave velocity and other physical properties. A set of survey lines were allotted to transect across the buried valley, and the survey successfully delineated the near-surface sedimentary structure in the buried valley.