Fracture detection in crystalline rock using ultrasonic shear waves
An ultrasonic shear wave reflection profiling system for use in the detection of water-filled cracks occurring within a crystalline rock mass is being tested in a laboratory environment. Experiments were performed on an irregular tensile crack induced approximately 0.5 m below one circular face of a 1.0-m-dia, 1.8-m-long granite cylinder. Good reflection data were obtained from this irregular crack with the crack either air filled or water filled. Data were collected that suggest a frequency-dependent S/sub H/ wave reflection coefficient for a granite-water interface. Waves that propagate along the free surface of a rock mass (surface waves) can severely hinder the detection of reflected events. Two methods of reducing this surface wave noise were investigated. The first technique uses physical obstructions (such as a slit trench) to scatter the surface waves. The second technique uses a linear array of receivers located on the free surface to cancel waves that are propagating parallel to the array (e.g., surface waves), thus enhancing waves with propagation vectors orthogonal to the linear array (e.g., reflected events). Deconvolution processing was found to be another method useful in surface wave cancellation.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 6082110
- Report Number(s):
- LBL-7051; SAC-19; TRN: 79-019152
- Country of Publication:
- United States
- Language:
- English
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58 GEOSCIENCES
GEOLOGIC FISSURES
DETECTION
ROCKS
SEISMIC SURVEYS
CRACKS
GEOLOGIC DEPOSITS
RADIOACTIVE WASTE DISPOSAL
REFLECTION
SHEAR
ULTRASONIC WAVES
WATER
WAVE PROPAGATION
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
HYDROGEN COMPOUNDS
MANAGEMENT
OXYGEN COMPOUNDS
SOUND WAVES
WASTE DISPOSAL
WASTE MANAGEMENT
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