Characterization of subsurface artificial fracture by the TFC/3DTFC method

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(a)Field Studies: Crosshole seismic measurement at Tohoku University Higashi-Hachimantai Field was carried out. Downhole airgun was used as a seismic source and signals transmitted through artificially pressurized fracture was recorded. The state of pressurization, location of source and detector were changed.(b)Analysis by the TFC/3DTFC method: The recorded signals in the field experiment were analyzed by the time-frequency coherency (TFC) and by the 3D-TFC methods. Some coherent components including direct arrivals, reflected phase and unknown coherent waves were discriminated.(c)Interpretation: Possible physics to generate coherent waves from pressurised fracture was investigated using theory of elastic wave. It has been concluded that leaky guided waves propagating along fracture is the most possible origin of detected coherent waves with lower velocity and highly correlated to pressurization.