Measurement of seismic signal while drilling using small-size downhole three component seismic detector and estimation of subsurface structure

A geophysical prospecting technique using seismic signal while drilling has been applied to a relatively small-scale drilling in a civil engineering such for high level nuclear waste disposal repository. For the purpose of it, a small-size downhole three component seismic detector was developed for measuring drilling signal. Then, the performance of the measurement system was verified by a calibration test using an artificial seismic source. A data acquisition of in-situ drilling signal was conducted during a drilling at a granitic quarry, and subsurface structure were estimated by the triaxial drillbit VSP method. The distribution of underground reflection coefficients was obtained to a depth of about 300 m by drilling signals from only 10 m drilling, and the estimated image agrees well with other borehole observations. (author)