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Comparative geometry of the San Andreas fault, California, and laboratory fault zones
GEOMECHANICS ABSTRACTS
921004 Analysis of bedrock structural fabric on the Wasatch Front, Utah Ala, S Proc 1990 Annual Symposium on Geology and Geotectmical Engineering, Instrumentation and Computer Applications, Pocatello, 4-6 April 1990 P22.1-22.17. Publ Pocatello: Idaho State University, 1990
Geology Tectonic processes and structural geology See also. 921056, 921061 921001 Comparative geometry of the San Andreas fault, California, and laboratory fault zones Moore, D E; Byerlee, J D Bull Geol Soc Am VI03, N6, June 1991, P762-774 The general correlation between fracture patterns of natural fault zones and those developed in laboratory shear and friction tests is well established. It is possible to distinguish stably sliding and stick slip samples in the laboratory on the basis of differences in orientations of secondary shear sets. To see if this feature can be extended to a much large scale, surface rupture patterns along the San Andreas fault zone have been studied, with emphasis on comparison of creeping and locked parts. Initial results are presented. They may be applicable to earthquake studies.
In the western flank of the Wasatch Range, the bedrock is Precambrian crystalline with negligible primary porosity. Groundwater flow is thus controlled by fractures. Remote and direct means have been used to map bedrock structure. Length, spacing, and orientation of fractures have been analysed with respect to lithology, faults, and topography. Data indicate that the shallow bedrock behaves like an isotropic porous medium,whilst on the larger scale, structural lineations are anisotropic. Deeper structural features may exert a more anisotropic and heterogeneous control over groundwater flow directions.
921002 Fractal patterns of fractures in granites Velde, B; Dubois, J; Moore, D; Touchard, G Earth Planet Sci Lett VI04, NI, May 1991, P25-35
921005 Modelling incipient tectonic faulting in the brittle crust of the earth Mandl, G Proc International Conference on Mechanics of Jointed and Faulted Rock, Vienna, 18-20 April 1990 P29-40. Publ Rotterdam: A A Balkema, 1990
Fractal measurements by the Cantor's dust method in a linear 1D analysis mode were made on fracture patterns on 2D planar surfaces of four granites. For the Sierra Nevada batholith, the value of D was essentially the same over 5 orders of magnitude of scale of measurement. The Boulder batholith, Montana, showed similar fractal values at different depth over a 700m depth interval. Investigations at a batholith in central France and in experimental deformations indicate that fracture planes of different origin can be characterised by different fractal values.
Tectonic faults are narrow zones of concentrated shearing, formed by a gradual process of shear concentration and localisation within a wider zone of predominantly inelastically deformed and damaged rock (process zone). The early stages of shear concentration determine location, shape, and spacing of faults. A numerical model to simulate faulting is developed. It is based on elastic/frictional plastic behaviour. It is illustrated using schematic geological examples and comparison is made with application of LEFM or Mohr-Coulomb slip concept approaches.
921003 Spatially heterogeneous strength in thrust fault zones Erickson, S G; Wiltschko, D V J Geophys Res V96, NB5, May 1991, P8427-8439
9210O6 Healed microcracks in granitic rocks and their use in paleostress analysis Kowallis, B J; Best, M G; Wang, H F; Jang, B A; Ren, X Proc International Conference on Mechanics of Jointed and Faulted Rock, Vienna, 18-20 April 1990 P137-140. Publ Rotterdam: A A Balkema, 1990
Deformation of the hanging wall of the Lewis thrust fault at Marias Pass, Montana, is heterogeneous, characterised by kilometer scale regions dominated by large scale contractual or extensional deformation. The density of fractures is highest under the extensional regime, density of solution features greatest under the contractual regime. An explanation of this deformation is proposed, based on spatially heterogeneous strength of the underlying fault zone. This is substantiated by analytical studies which simulate state of stress, fracture locations and orientations, and displacements in a thrust sheet overlying a fault with spatially variable shear resistance.
Examination of microcracks has been used to help in understanding the paleostress history of Precambrian granites in the Midcontinent and Basin and Range regions of the USA. Thin sections from granite samples were used in analysis and study of the healed cracks, fluid inclusion planes, and their orientations, from which in situ stress orientations can be established. Details of the study are presented.
© 1992 Pergamon Press plc. Reproduction not permitted IA
921004 Analysis of bedrock structural fabric on the Wasatch Front, Utah Ala, S Proc 1990 Annual Symposium on Geology and Geotectmical Engineering, Instrumentation and Computer Applications, Pocatello, 4-6 April 1990 P22.1-22.17. Publ Pocatello: Idaho State University, 1990
Geology Tectonic processes and structural geology See also. 921056, 921061 921001 Comparative geometry of the San Andreas fault, California, and laboratory fault zones Moore, D E; Byerlee, J D Bull Geol Soc Am VI03, N6, June 1991, P762-774 The general correlation between fracture patterns of natural fault zones and those developed in laboratory shear and friction tests is well established. It is possible to distinguish stably sliding and stick slip samples in the laboratory on the basis of differences in orientations of secondary shear sets. To see if this feature can be extended to a much large scale, surface rupture patterns along the San Andreas fault zone have been studied, with emphasis on comparison of creeping and locked parts. Initial results are presented. They may be applicable to earthquake studies.
In the western flank of the Wasatch Range, the bedrock is Precambrian crystalline with negligible primary porosity. Groundwater flow is thus controlled by fractures. Remote and direct means have been used to map bedrock structure. Length, spacing, and orientation of fractures have been analysed with respect to lithology, faults, and topography. Data indicate that the shallow bedrock behaves like an isotropic porous medium,whilst on the larger scale, structural lineations are anisotropic. Deeper structural features may exert a more anisotropic and heterogeneous control over groundwater flow directions.
921002 Fractal patterns of fractures in granites Velde, B; Dubois, J; Moore, D; Touchard, G Earth Planet Sci Lett VI04, NI, May 1991, P25-35
921005 Modelling incipient tectonic faulting in the brittle crust of the earth Mandl, G Proc International Conference on Mechanics of Jointed and Faulted Rock, Vienna, 18-20 April 1990 P29-40. Publ Rotterdam: A A Balkema, 1990
Fractal measurements by the Cantor's dust method in a linear 1D analysis mode were made on fracture patterns on 2D planar surfaces of four granites. For the Sierra Nevada batholith, the value of D was essentially the same over 5 orders of magnitude of scale of measurement. The Boulder batholith, Montana, showed similar fractal values at different depth over a 700m depth interval. Investigations at a batholith in central France and in experimental deformations indicate that fracture planes of different origin can be characterised by different fractal values.
Tectonic faults are narrow zones of concentrated shearing, formed by a gradual process of shear concentration and localisation within a wider zone of predominantly inelastically deformed and damaged rock (process zone). The early stages of shear concentration determine location, shape, and spacing of faults. A numerical model to simulate faulting is developed. It is based on elastic/frictional plastic behaviour. It is illustrated using schematic geological examples and comparison is made with application of LEFM or Mohr-Coulomb slip concept approaches.
921003 Spatially heterogeneous strength in thrust fault zones Erickson, S G; Wiltschko, D V J Geophys Res V96, NB5, May 1991, P8427-8439
9210O6 Healed microcracks in granitic rocks and their use in paleostress analysis Kowallis, B J; Best, M G; Wang, H F; Jang, B A; Ren, X Proc International Conference on Mechanics of Jointed and Faulted Rock, Vienna, 18-20 April 1990 P137-140. Publ Rotterdam: A A Balkema, 1990
Deformation of the hanging wall of the Lewis thrust fault at Marias Pass, Montana, is heterogeneous, characterised by kilometer scale regions dominated by large scale contractual or extensional deformation. The density of fractures is highest under the extensional regime, density of solution features greatest under the contractual regime. An explanation of this deformation is proposed, based on spatially heterogeneous strength of the underlying fault zone. This is substantiated by analytical studies which simulate state of stress, fracture locations and orientations, and displacements in a thrust sheet overlying a fault with spatially variable shear resistance.
Examination of microcracks has been used to help in understanding the paleostress history of Precambrian granites in the Midcontinent and Basin and Range regions of the USA. Thin sections from granite samples were used in analysis and study of the healed cracks, fluid inclusion planes, and their orientations, from which in situ stress orientations can be established. Details of the study are presented.
© 1992 Pergamon Press plc. Reproduction not permitted IA