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Tadashi Maruyama - One of the best experts on this subject based on the ideXlab platform.
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late quaternary activity and dextral strike slip movement on the karakax fault zone northwest tibet
Tectonophysics, 2008Co-Authors: Aiming Lin, Kenichi Kano, Jianming Guo, Tadashi MaruyamaAbstract:Abstract Field observations and interpretations of satellite images reveal that the westernmost segment of the Altyn Tagh Fault (called Karakax Fault Zone) striking WNW located in the northwestern margin of the Tibetan Plateau has distinctive geomorphic and tectonic features indicative of right-lateral strike-slip fault in the Late Quaternary. South-flowing gullies and N–S-trending ridges are systematically deflected and offset by up to ~ 1250 m, and Late Pleistocene–Holocene alluvial fans and small gullies that incise south-sloping fans record dextral offset up to ~ 150 m along the fault zone. Fault scarps developed on alluvial fans vary in height from 1 to 24 m. Riedel composite fabrics of foliated cataclastic rocks including cataclasite and fault gouge developed in the shear zone indicate a principal right-lateral shear sense with a Thrust Component. Based on offset Late Quaternary alluvial fans, 14 C ages and composite fabrics of cataclastic fault rocks, it is inferred that the average right-lateral strike-slip rate along the Karakax Fault Zone is ~ 9 mm/a in the Late Quaternary, with a vertical Component of ~ 2 mm/a, and that a M 7.5 morphogenic earthquake occurred along this fault in 1902. We suggest that right-lateral slip in the Late Quaternary along the WNW-trending Karakax Fault Zone is caused by escape tectonics that accommodate north–south shortening of the western Tibetan Plateau due to ongoing northward penetration of the Indian plate into the Eurasian plate.
Wayne Thatcher - One of the best experts on this subject based on the ideXlab platform.
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faulting geometry and slip from co seismic elevation changes the 18 october 1989 loma prieta california earthquake
Bulletin of the Seismological Society of America, 1991Co-Authors: Grant Marshall, Ross S Stein, Wayne ThatcherAbstract:Abstract Leveling surveys conducted before and after the Loma Prieta earthquake provide observations of the co-seismic elevation changes. These data are used to determine the faulting geometry and distribution of slip, considering planar, listric, and negatively listric fault shapes. Both the planar and nonplanar models produce elevation changes consistent with the observations. Most of the observed elevation changes can be modeled with a rupture surface that extends from 4- to 15-km depth. If the rupture surface is planar, the observations require 2.4 m of right-lateral strike slip and 1.7 m of reverse slip on a 34-km-long plane that dips 60°SW. The best-fitting model faults lie above and to the southwest of the aftershock zone. A significantly better fit to the observations is obtained when these fault geometries are allowed to have two rake values, with a larger Thrust Component northwest of the epicenter and a larger strike-slip Component southeast of the epicenter. When a low-modulus layer over a half-space is used for consistency with the seismic P -wave velocity structure, the fault deepens, coming within 3 km of the hypocenter, but still locates several kilometers southwest of most aftershocks.
Grant Marshall - One of the best experts on this subject based on the ideXlab platform.
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faulting geometry and slip from co seismic elevation changes the 18 october 1989 loma prieta california earthquake
Bulletin of the Seismological Society of America, 1991Co-Authors: Grant Marshall, Ross S Stein, Wayne ThatcherAbstract:Abstract Leveling surveys conducted before and after the Loma Prieta earthquake provide observations of the co-seismic elevation changes. These data are used to determine the faulting geometry and distribution of slip, considering planar, listric, and negatively listric fault shapes. Both the planar and nonplanar models produce elevation changes consistent with the observations. Most of the observed elevation changes can be modeled with a rupture surface that extends from 4- to 15-km depth. If the rupture surface is planar, the observations require 2.4 m of right-lateral strike slip and 1.7 m of reverse slip on a 34-km-long plane that dips 60°SW. The best-fitting model faults lie above and to the southwest of the aftershock zone. A significantly better fit to the observations is obtained when these fault geometries are allowed to have two rake values, with a larger Thrust Component northwest of the epicenter and a larger strike-slip Component southeast of the epicenter. When a low-modulus layer over a half-space is used for consistency with the seismic P -wave velocity structure, the fault deepens, coming within 3 km of the hypocenter, but still locates several kilometers southwest of most aftershocks.
Aiming Lin - One of the best experts on this subject based on the ideXlab platform.
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late quaternary activity and dextral strike slip movement on the karakax fault zone northwest tibet
Tectonophysics, 2008Co-Authors: Aiming Lin, Kenichi Kano, Jianming Guo, Tadashi MaruyamaAbstract:Abstract Field observations and interpretations of satellite images reveal that the westernmost segment of the Altyn Tagh Fault (called Karakax Fault Zone) striking WNW located in the northwestern margin of the Tibetan Plateau has distinctive geomorphic and tectonic features indicative of right-lateral strike-slip fault in the Late Quaternary. South-flowing gullies and N–S-trending ridges are systematically deflected and offset by up to ~ 1250 m, and Late Pleistocene–Holocene alluvial fans and small gullies that incise south-sloping fans record dextral offset up to ~ 150 m along the fault zone. Fault scarps developed on alluvial fans vary in height from 1 to 24 m. Riedel composite fabrics of foliated cataclastic rocks including cataclasite and fault gouge developed in the shear zone indicate a principal right-lateral shear sense with a Thrust Component. Based on offset Late Quaternary alluvial fans, 14 C ages and composite fabrics of cataclastic fault rocks, it is inferred that the average right-lateral strike-slip rate along the Karakax Fault Zone is ~ 9 mm/a in the Late Quaternary, with a vertical Component of ~ 2 mm/a, and that a M 7.5 morphogenic earthquake occurred along this fault in 1902. We suggest that right-lateral slip in the Late Quaternary along the WNW-trending Karakax Fault Zone is caused by escape tectonics that accommodate north–south shortening of the western Tibetan Plateau due to ongoing northward penetration of the Indian plate into the Eurasian plate.
Arthur G Goldstein - One of the best experts on this subject based on the ideXlab platform.
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a shear zone origin for alleghanian permian multiple deformation in eastern massachusetts
Tectonics, 1994Co-Authors: Arthur G GoldsteinAbstract:The area around Worcester, Massachusetts, has been used to determine which deformational and metamorphic features are due to the Alleghanian (Permian) orogeny and which are pre-Alleghanian. Isolated, fault-bounded inliers of Carboniferous rocks display evidence of a single metamorphism and the formation of two prominent cleavages. The first cleavage formed synchronously with metamorphism. Pre-Carboniferous metasedimentary rocks have been affected by two metamorphisms and contain three prominent cleavages. The initial cleavage formed during the first metamorphism and the second cleavage formed during the second, retrogressive metamorphism. Thus the second two cleavages and the second metamorphism in pre-Carboniferous rocks are interpreted as Alleghanian. Normal displacements on two distinct faults are bracketed by the formation of the first and second Alleghanian cleavages. The initial faulting, along the newly defined Wachusett mylonite zone (WMZ), formed a wide zone of ductile mylonites which dips moderately to the northwest and contains elongation lineations which trend northwest. The second faulting, along the Clinton-Newbury fault (CNF) occurred along a steeply inclined plane which cuts the WMZ mylonites and contains a thin zone of phyllonites and mylonites which have elongation lineations which trend west. Alleghanian cleavages and metamorphism are confined to a mappable zone which is approximately 15 km wide where well defined. This zone is interpreted as a ductile shear zone which moved twice, forming the first and second Alleghanian cleavages. Early-formed, pre-Alleghanian metamorphic minerals are retrograded to hydrous phyllosilicates, and new hydrous minerals formed in the shear zone, indicating that it was a pathway for fluid flow. The initial motion was left-lateral with a Thrust Component. The second cleavage formed during top-to-the-northwest normal displacements. Thus the history of Alleghanian tectonism in this area began with sinistral faulting and then included three displacements along normal faults or shear zones. This suggests that the strain history included two distinct episodes, with the second experiencing slightly different strain orientations at different times, resulting in first WMZ normal motion, then CNF normal motion and finally normal displacements related to the second Alleghanian cleavages. This history agrees well with other work on the nature of the Alleghanian orogeny in the northeast United States.