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Joint Analysis of a Surface-wave Method and Micro-gravity Survey

¹ Tsukuba Technical Research and Development Center, OYO Corporation, 43, Miyukigaoka, Tsukuba, Ibaraki, 305-0841, Japan
² Department of Civil and Earth Resources Engineering, Kyoto University, Yoshida-honmachi, Sakyou-ku, 606-8501, Kyoto, Japan
³ Energy division, OYO Corporation, 2-2-19, Daitakubo, Saitama, Saitama, 336-0015, Japan

We propose a joint analysis of a surface-wave and a micro-gravity survey for estimating both S-wave velocity and density of the subsurface. The surface-wave method and micro-gravity surveys were performed to delineate a buried channel filled with soft alluvium sediments. A CMP cross-correlation analysis of surface-waves was applied to multi-shot and multi-channel surface-wave data and an S-wave velocity model was estimated. A micro-gravity survey was performed on the same survey line and a clear Bouguer anomaly low was detected. The S-wave velocity model was converted into a density model by a transform developed by combining density from laboratory soil tests and the S-wave model. The theoretical gravity anomaly was calculated, and compared well with the observed data, supporting the accuracy of the assumed transform. This density model was used as the initial model in a least squares inversion and a clear low-density area was obtained, which agrees with a low S-wave velocity area obtained from the surface-wave method. The two images are combined to estimate the shear modulus, and the lateral extent of the buried channel is clearly delineated.