Velocity analysis of CMP gathers acquired by an array GPR system ‘Yakumo’: results from field application to tsunami deposits

This paper examines the capability of a multi-static ground penetrating radar (GPR) system ‘Yakumo’ to estimate a vertical profile of dielectric constants of stratified geological layers. Yakumo is equipped with eight transmitting and eight receiving antennas. By using Yakumo, we propose to obtain an eight-channel common mid-point (CMP) gather from the 64-channel multi-static radar dataset acquired at each point on the survey line. From each CMP gather, a vertical profile of interval velocities can be estimated by velocity spectrum analysis. By a laboratory sandbox experiment, we validate that the thickness of an 83 cm sand layer is estimated with an error of less than 4%. A field survey carried out on tsunami deposits demonstrates that our GPR method can provide the spatial distribution of layer velocities of the sedimentary structure and that the results are comparable with the geological logs at three points and a conventional common-offset GPR profile.