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| index | Vol. 48 | 1 | 2 | 3/4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | Japanese Index | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Preface of a special issue on experimental studies related to earthquake
Takashi Satoh and Koji Masuda
1997
vol. 48 (8), p. 429.
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New multi-wire type and co-axial type feedthroughs for oil pressure-medium vessel
Osamu Nishizawa
1997
vol. 48 (8), p. 431-438, 9 figs.
Keywords: multi-wire feedthrough, co-axial feedthrough, high-pressure vessel
Abstract: New multi-wire type and co-axial type feedthroughs for an oil pressure-medium vessel were developed. The multi-wire type feedthrough is used for acquiring data from strain gauges, and the co-axial type is used for acquiring elastic waveforms detected by piezoelectric transducers. The multi-wire type feedthrough contains four wires, which are led out through a 2-mm-diameter through-hole drilled in a vessel closure. The co-axial type feedthrough reduces the noise level by insulating the shield wire from the vessel. Both types of feedthroughs are designed on the basis of Bridgman's self-sealing mechanism with unsupported area, which realizes tighter sealing as pressure increases. Because only O-rings are used for gaskets, feedthroughs can endure repeated use up to 200 MPa and also allows easy manipulation for installation or removal, so that we can easily change electrode arrangements.
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A high-speed, multi-channel waveform recording system for AE measurement
Takashi Satoh and Osamu Nishizawa
1997
vol. 48 (8), p. 439-446, 7 figs., 2 tables.
Keywords: acoustic emission (AE), rock fracture experiment, microfracturing, AE measurement system
AbstractFTo investigate detailed features of the space-time distributions of microfractures generated during rock fracture experiments, we have developed a new high-speed, multi-channel acoustic emission (AE) waveform recording system. The system consists of 32 channels of transient-memory controlled by a microcomputer. The transient-memory has a 16MB RAM buffer in each channel. The large amount of RAM buffer enables us to record more than 8000 AE events with very short system dead-time, which is the time interval in which we are unable to detect an AE event due to recording of waveform data. The dead-time is about 200 s before the RAM buffer becomes full, and about 0.4 s afterwards. The newly-introduced controller, which can check the status of the RAM buffer, synchronizes the transient-memory so that all channels can record an AE event at the same time even after the RAM has been filled. Using this system, we clearly found clustering of AE hypocenters around a macroscopic fracture plane during a 10 second interval before final fracture of a granite sample under triaxial compression. This demonstrates that the new system could be a very powerful tool for studying the space-time distribution of AE events, especially when the AE activity is very high.
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An AE data processing program for Windows
Xinglin Lei, Osamu Nishizawa, Takashi Satoh and Kinichiro Kusunose
1997
vol. 48 (8), p. 447-457, 13 figs.
Keywords: acoustic emission, fracture, fractal, hypocenter distribution, mechanism solution, data processing, computer software
Abstract: For dealing with the huge data sets acquired during AE experiments, we have developed a visual and interactive program (WinAE) for data acquisition and processing. This program can create more than 10 types of time-space distribution maps of AE events and can perform statistical analyses. The main utilities of WinAE are: 1) acquisition of AE waveform data through GPIB; 2) automatic picking of P arrival times and hypocenter determination; 3) manual picking of P arrival times and hypocenter re-determination; 4) time distribution maps of AE events; 5) spatial distribution maps of AE hypocenters, such as cross profile, cylindrical and stereo projections; 6) parameter estimations for generalized two point correlation integers and a potential model for AE hypocenter distributions; 7) point process model analysis; 8) automatic or manual focal mechanism solution; and 9) AE time-space distribution analyses with respect to source mechanism. Thus, WinAE is useful for studying the properties of the fracturing process in stressed rock samples.
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A high-pressure, high-temperature rock testing apparatus installed at the Geological Survey of Japan|The axial stess drop process in the post-failue region of Westerly graite|
Akio Cho and Hironori Kawakata
1997
vol. 48 (8), p. 459-468, 11 figs.
Keywords: triaxial test, high-pressure vessel, controlled clearance bearing, granite, fracture, X-ray CT scan
Abstract: A high-pressure, high-temperature rock testing apparatus was installed at the GSJ in 1994. The pressure vessel can achieve a confining pressure of up to 500 MPa and a temperature of up to 300. The vessel has 24 electrical feedthroughs and 2 pore pressure feedthroughs. Specimens 50 mm in diameter and 100 mm in length can be tested.
Using this apparatus, dry Westerly granite specimens were loaded under a confining pressure of 100 MPa, and the fracture process was controlled by maintaining a constant rate of circumferential displacement. The specimens were then unloaded from the post-failure region, and their interiors were observed by an X-ray CT scan.
@The axial stress drop process in the post-failure region was composed of three stages. In the first stage, the stress drop rate was very slow (several MPa/min), and many cracks were observed on the specimen's surface. In the second stage, the stress drop rate became ten times faster than in the previous stage. A shear fracture nucleated near the specimen surface and grew stably toward the specimen interior. In the final stage, the fracture penetrated dynamically through the specimen accompanied by a dramatic acceleration of the stress drop.
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Fracture planes observed with X-ray CT images and AE hypocenter distribution
Koji Masuda, Laurence Jouniaux, Osamu Nishizawa, Xinglin Lei, Liqiang Liu, Wentao Ma, Takashi Satoh and Kinichiro Kusunose
1997
vol. 48 (8), p. 469-473, 5 figs.
Keywords: X-ray CT, AE, fracture plane
Abstract: Images of fracture planes were obtained by acoustic emission (AE) hypocenter distribution and X-ray CT for a granite rock sample that was fractured under tri-axial conditions. The AE hypocenter distribution reveals the fracture plane during the experiment, whereas X-ray CT images are created before and after the experiment. Two fracture planes were observed in the X-ray CT image, whereas only one fracture plane was observed in the AE hypocenter distribution. This suggests that the time of formation was different for the two fractures.
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Effects of water on deformation and fracture process of rocks |Experimental study|
Koji Masuda, Takashi Satoh and Osamu Nishizawa
1997
vol. 48 (8), p. 475-485, 12 figs.
Keywords: water effect, rock deformation, rock fracture, rock mechanics, earthquake, P-wave velocity, P-wave tomography, induced seismicity, acoustic emission, stress corrosion
Abstract: We review the experimental studies on the effects of water on deformation and fracture of rocks. Failure strength of granite and andesite has been measured under various conditions of strain-rate and confining pressure both in dry and wet states. The failure strength decreases linearly as the logarithm of the strain rate decreases. The strain-rate effect on the failure strength of wet samples is more apparent than on the failure strength of dry samples. The triggering of seismicity by fluid flow or water pressure change underground is controlled by the pre-existing in situ differential stress in the crust. During water infiltration into a dry granite in the dilatant state, in which a rock is subjected to differential stress near the failure strength, migration of a water front and a clear relationship between acoustic emission (AE) activity and water flow into microcracks were revealed by means of AE hypocenter location and P-wave velocity tomography. We will investigate the effects of the inhomogeneity of the rock structure on the induced seismicity by the infiltrated water. We need further study on the effects of fluids, such as chemical effects on rock physical properties at high temperature.
