| Abstract: | In uniaxial compression tests performed on Aue granite cores (diameter 50 mm, length 100 mm), a steel loading plate was used to induce the formation of a discrete shear fracture. A zone of distributed microcracks surrounds the tip of the propagating fracture. This process zone is imaged by locating acoustic emission events using 12 piezoceramic sensors attached to the samples. Propagation velocity of the process zone is varied by using the rate of acoustic emissions to control the applied axial force. The resulting velocities range from 2 mm/s in displacement-controlled tests to 2 ??m/s in tests controlled by acoustic emission rate. Wave velocities and amplitudes are monitored during fault formation. P waves transmitted through the approaching process zone show a drop in amplitude of 26 dB, and ultrasonic velocities are reduced by 10%. The width of the process zone is ???9 times the grain diameter inferred from acoustic data but is only 2 times the grain size from optical crack inspection. The process zone of fast propagating fractures is wider than for slow ones. The density of microcracks and acoustic emissions increases approaching the main fracture. Shear displacement scales linearly with fracture length. Fault plane solutions from acoustic events show similar orientation of nodal planes on both sides of the shear fracture. The ratio of the process zone width to the fault length in Aue granite ranges from 0.01 to 0.1 inferred from crack data and acoustic emissions, respectively. The fracture surface energy is estimated from microstructure analysis to be ???2 J. A lower bound estimate for the energy dissipated by acoustic events is 0.1 J. Copyright 2000 by the American Geophysical Union. |
| Genre: | Article |
| ProdID: | 70022359 |
| Citation Author: | Zang, A.; Wagner, F. C.; Stanchits, S.; Janssen, C.; Dresen, G. |
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| Citation End Page: | 23661 |
| Citation Issue: | B10 |
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| Citation Language: | English |
| Citation Larger Work Title: | Journal of Geophysical Research B: Solid Earth |
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| Citation Number Of Pages: | 11 |
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| Citation Search Results Text: | Fracture process zone in granite; 2000; Article; Journal; Journal of Geophysical Research B: Solid Earth; Zang, A.; Wagner, F. C.; Stanchits, S.; Janssen, C.; Dresen, G. |
| Citation Start Page: | 23651 |
| Citation Volume: | 105 |
| Citation Year: | 2000 |
| Type: | citation/reference |
| Text: | Fracture process zone in granite; 2000; Article; Journal; Journal of Geophysical Research B: Solid Earth; Zang, A.; Wagner, F. C.; Stanchits, S.; Janssen, C.; Dresen, G. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Sat, 1 Jan 2000 00:00 -0600 |
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