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| | Abstract | | The purpose of this study is to develop the new data acquisition system to explore accurately the fracture, water pass way, in hard rocks. We made the rock model of 0.5m scales including one or two fractures. The aperture is 0.2 to 2 mm by stacking two blocks of granite and the interval of two fractures are set ranged from 5 to 10 cm. The acoustic tomography was conducted using the rock model. The frequency of the transmitter ranges from 31 to 150 kHz. P-wave velocity section and attenuation section were analyzed by 3D inversion techniques. As the result, the fractures with 0.2 mm aperture and the 10cm interval were explored clearly in the attenuation section. Next, the acoustic tomography using five boreholes was conducted at the Grimsel Test Site in Switzerland. The frequency of the transmitter ranges from 10 to 30 kHz. We corrected the influence of velocity anisotropic based on a forward modeling for the measurement data and analyzed attenuation sections by 3D inversion techniques. As a result, a few high attenuation zones were detected, which correspond to high permeable fracture zones realized by the results of permeability tests and the BTV observations. It is indicated that the acoustic tomography is applicable to explore the fracture zone in hard rocks. |
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