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Robert Mccaffrey - One of the best experts on this subject based on the ideXlab platform.
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fault locking block rotation and crustal deformation in the pacific northwest
Geophysical Journal International, 2007Co-Authors: Robert Mccaffrey, Anthony Qamar, R W King, Ray E Wells, Giorgi Khazaradze, C A Williams, C Stevens, Jesse J Vollick, Peter C ZwickAbstract:SUMMARY We interpret Global Positioning System (GPS) measurements in the northwestern United States and adjacent parts of western Canada to describe relative motions of crustal blocks, locking on faults and permanent deformation associated with convergence between the Juan de Fuca and North American plates. To estimate angular velocities of the oceanic Juan de Fuca and Explorer plates and several continental crustal blocks, we invert the GPS velocities together with seafloor spreading rates, earthquake Slip Vector azimuths and fault Slip azimuths and rates. We also determine the degree to which faults are either creeping aseismically or, alternatively, locked on the block-bounding faults. The Cascadia subduction thrust is locked mainly offshore, except in central Oregon, where locking extends inland. Most of Oregon and southwest Washington rotate clockwise relative to North America at rates of 0.4–1.0 ° Myr–1. No shear or extension along the Cascades volcanic arc has occurred at the mm/yr level during the past decade, suggesting that the shear deformation extending northward from the Walker Lane and eastern California shear zone south of Oregon is largely accommodated by block rotation in Oregon. The general agreement of vertical axis rotation rates derived from GPS velocities with those estimated from palaeomagnetic declination anomalies suggests that the rotations have been relatively steady for 10–15 Ma. Additional permanent dextral shear is indicated within the Oregon Coast Range near the coast. Block rotations in the Pacific Northwest do not result in net westward flux of crustal material—the crust is simply spinning and not escaping. On Vancouver Island, where the convergence obliquity is less than in Oregon and Washington, the contractional strain at the coast is more aligned with Juan de Fuca—North America motion. GPS velocities are fit significantly better when Vancouver Island and the southern Coast Mountains move relative to North America in a block-like fashion. The relative motions of the Oregon, western Washington and Vancouver Island crustal blocks indicate that the rate of permanent shortening, the type that causes upper plate earthquakes, across the Puget Sound region is 4.4 ± 0.3 mm yr–1. This shortening is likely distributed over several faults but GPS data alone cannot determine the partitioning of Slip on them. The transition from predominantly shear deformation within the continent south of the Mendocino Triple Junction to predominantly block rotations north of it is similar to changes in tectonic style at other transitions from shear to subduction. This similarity suggests that crustal block rotations are enhanced in the vicinity of subduction zones possibly due to lower resisting stress.
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microblock rotations and fault coupling in se asia triple junction sulawesi indonesia from gps and earthquake Slip Vector data
Journal of Geophysical Research, 2006Co-Authors: Robert Mccaffrey, A Socquet, W J F Simons, C Vigny, C Subarya, Dina Sarsito, B A C Ambrosius, Wim SpakmanAbstract:The island of Sulawesi, eastern Indonesia, is located within the triple junction of the Australian, Philippine, and Sunda plates and accommodates the convergence of continental fragments with the Sunda margin. We quantify the kinematics of Sulawesi by modeling GPS velocities and earthquake Slip Vectors as a combination of rigid block rotations and elastic deformation around faults. We find that the deformation can be reasonably described by a small number of rapidly rotating crustal blocks. Relative to the Sunda Plate, the southwestern part of Sulawesi (Makassar Block) rotates anticlockwise at ?1.4°/Myr. The northeastern part of Sulawesi, the Bangai?Sula domain, comprises three blocks: the central North Sula Block moves toward the NNW and rotates clockwise at ?2.5°/Myr, the northeastern Manado Block rotates clockwise at ?3°/Myr about a nearby axis, and East Sulawesi is pinched between the North Sula and Makassar blocks. Along the boundary between the Makassar Block and the Sunda Plate, GPS measurements suggest that the trench accommodates ?15 mm/yr of Slip within the Makassar Strait with current elastic strain accumulation. The tectonic boundary between North Sula and Manado blocks is the Gorontalo Fault, moving right laterally at about 11 mm/yr and accumulating elastic strain. The 42 mm/yr relative motion between North Sula and Makassar blocks is accommodated on the Palu?Koro left?lateral strike?Slip fault zone. The data also indicate a pull?apart structure in Palu area, where the fault shows a transtensive motion and may have a complex geometry involving several active strands. Sulawesi provides a primary example of how collision can be accommodated by crustal block rotation instead of mountain building.
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Estimates of modern arc-parallel strain rates in fore arcs
Geology, 1996Co-Authors: Robert MccaffreyAbstract:Deflections of Slip Vectors of interplate thrust earthquakes from expected directions are used to estimate arc-parallel strain rates within the overriding plates at the world9s major convergent plate margins. Arc-parallel extension strain rates, between 10 −8 /yr and 10 −7 /yr and significant at 2 standard deviations, are observed in the fore arcs of the Aegean, Aleutian, Mariana, Sumatran, southern Kuriles, New Hebrides, Scotia, and southern Central American (lat 8° to 12°N) subduction zones and the Himalayas. Northern Chile (lat 17° to 31°S) and Central America (lat 11° to 18°N) show arc-parallel compression. Available geologic and geodetic estimates of fore-arc Slip and strain rates agree within a factor of two with Slip-Vector estimates. Arc-parallel strain in fore arcs is rapid enough to produce geologically significant effects, such as unroofing of high-grade metamorphic rocks and disruption of transported fore-arc terranes. Fore arcs deform even where convergence is perpendicular to curved margins, demonstrating that head-on subduction can produce a three-dimensional strain field.
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Global Variability in Subduction Thrust Zone-Forearc Systems
Pure and Applied Geophysics, 1994Co-Authors: Robert MccaffreyAbstract:Deviations of Slip Vector azimuths of interplate thrust earthquakes from expected plate convergence directions at oblique subduction zones provide kinematic information about the deformation of forearcs and indirect evidence on the dynamics of the plate boundary. A global survey of Slip Vectors at major trenches of the world reveals a large variability in the kinematic response of forearcs to shear produced by oblique convergence. The variability in forearc deformation inferred from Slip Vector deflections is suggested to be caused by variations in forearc rheology rather than in the stresses acting on subduction zone thrust faults. Estimated apparent macroscopic rheologies range from elastic to perfectly plastic (or viscous). Forearc rheologies inferred from Slip Vectors do not correlate with age of the subducting lithosphere, but continental forearcs or old arcs appear to deform less than oceanic or young arcs. The inferred absence of forearc deformation at continental arcs from this study is counter to inferences drawn from compiled geologic information on forearc faults. Correlations of the apparent forearc rheology with backarc spreading, convergence rate, slab dip, arc curvature, and downdip length of the thrust contact are poor. However, great subduction zone earthquakes occur where forearcs are apparently more elastic (i.e., less deformed by oblique convergence), which suggests that the mechanical properties of forearcs rather than stress magnitude on thrust faults control both the kinematic behavior of forearcs and where great subduction zone earthquakes occur.
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On the role of the upper plate in great subduction zone earthquakes
Journal of Geophysical Research, 1993Co-Authors: Robert MccaffreyAbstract:At subduction zones where convergence is not perpendicular to the trench (i.e., oblique), Slip Vectors of interplate thrust earthquakes are often systematically deflected away from the expected plate Vector, probably by deformation of the leading edge of the upper plate. Near the epicenters of great thrust earthquakes of Mw≥8.0 in this century that occurred at trenches, systematic deflections of Slip Vectors for recent (1977–1992.5) interplate thrust earthquakes are significantly less than global averages. Statistical tests show that great earthquakes nucleate where deviations of Slip Vectors (residuals) are smaller and plate convergence is faster but not preferentially where the angle of obliquity is smaller than global averages. The small Slip Vector residuals suggest that great earthquakes nucleate where forces in the forearc due to plate convergence are sustained elastically, rather than anelastically, and that shear stress on subduction thrust faults with great earthquakes is not necessarily higher than on faults without them. Shear stress magnitude is less important than rheology in determining the seismic behavior of subduction zones. An observed decrease in the Slip Vector residuals with increasing rates of trench-normal convergence is interpreted as evidence that the forearc is increasingly cooled and strengthened by faster subduction. For the forearc to cool with increasing convergence rate, the shear stress on the subduction thrust fault must be less than about 40 MPa. Lower temperatures on the fault surface and the possibility that thrust faults below undeforming forearcs are smoother than those below deforming forearcs both act to increase the frictional instability of the fault zone. Great thrust earthquakes at subduction zones seem to occur where convergence is fast and the forearc is cool and predominantly elastic. The ability of the forearc of the upper plate to store elastic strain energy appears to be a major factor controlling where great subduction thrust earthquakes can and cannot occur.
Jeanfrancois Ritz - One of the best experts on this subject based on the ideXlab platform.
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determining the Slip Vector by graphical construction use of a simplified representation of the stress tensor
Journal of Structural Geology, 1994Co-Authors: Jeanfrancois RitzAbstract:Abstract A classification of tectonic stress regimes and a simple graphical construction of the Slip Vector applied on a fault plane are proposed, from a simplified expression of the stress tensor such that its components depend only on the stress ellipsoid shape ratio.
A Socquet - One of the best experts on this subject based on the ideXlab platform.
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microblock rotations and fault coupling in se asia triple junction sulawesi indonesia from gps and earthquake Slip Vector data
Journal of Geophysical Research, 2006Co-Authors: Robert Mccaffrey, A Socquet, W J F Simons, C Vigny, C Subarya, Dina Sarsito, B A C Ambrosius, Wim SpakmanAbstract:The island of Sulawesi, eastern Indonesia, is located within the triple junction of the Australian, Philippine, and Sunda plates and accommodates the convergence of continental fragments with the Sunda margin. We quantify the kinematics of Sulawesi by modeling GPS velocities and earthquake Slip Vectors as a combination of rigid block rotations and elastic deformation around faults. We find that the deformation can be reasonably described by a small number of rapidly rotating crustal blocks. Relative to the Sunda Plate, the southwestern part of Sulawesi (Makassar Block) rotates anticlockwise at ?1.4°/Myr. The northeastern part of Sulawesi, the Bangai?Sula domain, comprises three blocks: the central North Sula Block moves toward the NNW and rotates clockwise at ?2.5°/Myr, the northeastern Manado Block rotates clockwise at ?3°/Myr about a nearby axis, and East Sulawesi is pinched between the North Sula and Makassar blocks. Along the boundary between the Makassar Block and the Sunda Plate, GPS measurements suggest that the trench accommodates ?15 mm/yr of Slip within the Makassar Strait with current elastic strain accumulation. The tectonic boundary between North Sula and Manado blocks is the Gorontalo Fault, moving right laterally at about 11 mm/yr and accumulating elastic strain. The 42 mm/yr relative motion between North Sula and Makassar blocks is accommodated on the Palu?Koro left?lateral strike?Slip fault zone. The data also indicate a pull?apart structure in Palu area, where the fault shows a transtensive motion and may have a complex geometry involving several active strands. Sulawesi provides a primary example of how collision can be accommodated by crustal block rotation instead of mountain building.
Larry H. Matthies - One of the best experts on this subject based on the ideXlab platform.
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Slip-compensated path following for planetary exploration rovers
Advanced Robotics, 2006Co-Authors: Daniel M Helmick, Daniel S Clouse, Max Bajracharya, Stergios I. Roumeliotis, Yang Cheng, Larry H. MatthiesAbstract:A system that enables continuous Slip compensation for a Mars rover has been designed, implemented and field-tested. This system is composed of several components that allow the rover to accurately and continuously follow a designated path, compensate for Slippage and reach intended goals in high-Slip environments. These components include visual odometry, vehicle kinematics, a Kalman filter pose estimator and a Slip-compensated path follower. Visual odometry tracks distinctive scene features in stereo imagery to estimate rover motion between successively acquired stereo image pairs. The kinematics for a rocker-bogie suspension system estimates vehicle motion by measuring wheel rates, and rocker, bogie and steering angles. The Kalman filter processes measurements from an inertial measurement unit and visual odometry. The filter estimate is then compared to the kinematic estimate to determine whether Slippage has occurred, taking into account estimate uncertainties. If Slippage is detected, the Slip Vector is calculated by differencing the current Kalman filter estimate from the kinematic estimate. This Slip Vector is then used to determine the necessary wheel velocities and steering angles to compensate for Slip and follow the desired path.
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IROS - Slip compensation for a Mars rover
2005 IEEE RSJ International Conference on Intelligent Robots and Systems, 2005Co-Authors: Daniel M Helmick, Daniel S Clouse, Larry H. Matthies, Max Bajracharya, Yang Cheng, Stergios I. RoumeliotisAbstract:A system that enables continuous Slip compensation for a Mars rover has been designed, implemented, and field-tested. This system is composed of several components that allow the rover to accurately and continuously follow a designated path, compensate for Slippage, and reach intended goals in high-Slip environments. These components include: visual odometry, vehicle kinematics, a Kalman filter pose estimator, and a Slip compensation/path follower. Visual odometry tracks distinctive scene features in stereo imagery to estimate rover motion between successively acquired stereo image pairs. The vehicle kinematics for a rocker-bogie suspension system estimates motion by measuring wheel rates, and rocker, bogie, and steering angles. The Kalman filter merges data from an inertial measurement unit (IMU) and visual odometry. This merged estimate is then compared to the kinematic estimate to determine how much Slippage has occurred, taking into account estimate uncertainties. If Slippage has occurred then a Slip Vector is calculated by differencing the current Kalman filter estimate from the kinematic estimate. This Slip Vector is then used to determine the necessary wheel velocities and steering angles to compensate for Slip and follow the desired path.
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Slip compensation for a mars rover
2005 IEEE RSJ International Conference on Intelligent Robots and Systems IROS, 2005Co-Authors: Daniel M Helmick, Daniel S Clouse, Larry H. Matthies, Max Bajracharya, Yang Cheng, Stergios I. RoumeliotisAbstract:A system that enables continuous Slip compensation for a Mars rover has been designed, implemented, and field-tested. This system is composed of several components that allow the rover to accurately and continuously follow a designated path, compensate for Slippage, and reach intended goals in high-Slip environments. These components include: visual odometry, vehicle kinematics, a Kalman filter pose estimator, and a Slip compensation/path follower. Visual odometry tracks distinctive scene features in stereo imagery to estimate rover motion between successively acquired stereo image pairs. The vehicle kinematics for a rocker-bogie suspension system estimates motion by measuring wheel rates, and rocker, bogie, and steering angles. The Kalman filter merges data from an inertial measurement unit (IMU) and visual odometry. This merged estimate is then compared to the kinematic estimate to determine how much Slippage has occurred, taking into account estimate uncertainties. If Slippage has occurred then a Slip Vector is calculated by differencing the current Kalman filter estimate from the kinematic estimate. This Slip Vector is then used to determine the necessary wheel velocities and steering angles to compensate for Slip and follow the desired path.
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Path following using visual odometry for a Mars rover in high-Slip environments
2004 IEEE Aerospace Conference Proceedings (IEEE Cat. No.04TH8720), 2004Co-Authors: Yang Cheng, Larry H. MatthiesAbstract:A system for autonomous operation of Mars rovers in high Slip environments has been designed, implemented, and tested. This system is composed of several key technologies that enable the rover to accurately follow a designated path, compensate for Slippage, and reach intended goals independent of the terrain over which it is traversing (within the mechanical constraints of the mobility system). These technologies include: visual odometry, full vehicle kinematics, a Kalman filter pose estimator, and a Slip compensation/path follower. Visual odometry tracks distinctive scene features in stereo imagery to estimate rover motion between successively acquired stereo image pairs using a maximum likelihood motion estimation algorithm. The full vehicle kinematics for a rocker-bogie suspension system estimates motion, with a no-Slip assumption, by measuring wheel rates, and rocker, bogie, and steering angles. The Kalman filter merges data from an inertial measurement unit (IMU) and visual odometry. This merged estimate is then compared to the kinematic estimate to determine (taking into account estimate uncertainties) if and how much Slippage has occurred. If no statistically significant Slippage has occurred then the kinematic estimate is used to complement the Kalman filter estimate. If Slippage has occurred then a Slip Vector is calculated by differencing the current Kalman filter estimate from the kinematic estimate. This Slip Vector is then used, in conjunction with the inverse kinematics, to determine the necessary wheel velocities and steering angles to compensate for Slip and follow the desired path.
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Path Following using Visual Odometry for
IEEE Aerospace Conference Proceedings, 2004Co-Authors: Daniel M Helmick, Daniel S Clouse, Yang Cheng, Larry H. MatthiesAbstract:An architecture for autonomous operation of Mars rovers in high Slip environments has been designed, implemented, and tested. This architecture is composed of several key technologies that enable the rover to accurately follow a designated path, compensate for Slippage, and reach intended goals independent of the terrain over which it is traversing (within the mechanical constraints of the mobility system). These technologies include: visual odometry, full vehicle kinematics, a Kalman filter, and a Slip compensation/path follower. Visual odometry tracks distinctive scene features in stereo imagery to estimate rover motion between successively acquired stereo image pairs using a maximum likelihood motion estimation algorithm. The full vehicle kinematics for a rocker-bogie suspension system estimates motion, with a no-Slip assumption, by measuring wheel rates, and rocker, bogie, and steering angles. The Kalman filter merges data from an Inertial Measurement Unit (IMU) and visual odometry. This merged estimate is then compared to the kinematic estimate to determine (taking into account estimate uncertainties) if and how much Slippage has occurred. If no statistically significant Slippage has occurred then the kinematic estimate is used to complement the Kalman filter estimate. If Slippage has occurred then a Slip Vector is calculated by differencing the current Kalman filter estimate from the kinematic estimate. This Slip Vector is then used, in conjunction with the inverse kinematics, to determine the necessary wheel velocities and steering angles to compensate for Slip and follow the desired path.
Wim Spakman - One of the best experts on this subject based on the ideXlab platform.
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microblock rotations and fault coupling in se asia triple junction sulawesi indonesia from gps and earthquake Slip Vector data
Journal of Geophysical Research, 2006Co-Authors: Robert Mccaffrey, A Socquet, W J F Simons, C Vigny, C Subarya, Dina Sarsito, B A C Ambrosius, Wim SpakmanAbstract:The island of Sulawesi, eastern Indonesia, is located within the triple junction of the Australian, Philippine, and Sunda plates and accommodates the convergence of continental fragments with the Sunda margin. We quantify the kinematics of Sulawesi by modeling GPS velocities and earthquake Slip Vectors as a combination of rigid block rotations and elastic deformation around faults. We find that the deformation can be reasonably described by a small number of rapidly rotating crustal blocks. Relative to the Sunda Plate, the southwestern part of Sulawesi (Makassar Block) rotates anticlockwise at ?1.4°/Myr. The northeastern part of Sulawesi, the Bangai?Sula domain, comprises three blocks: the central North Sula Block moves toward the NNW and rotates clockwise at ?2.5°/Myr, the northeastern Manado Block rotates clockwise at ?3°/Myr about a nearby axis, and East Sulawesi is pinched between the North Sula and Makassar blocks. Along the boundary between the Makassar Block and the Sunda Plate, GPS measurements suggest that the trench accommodates ?15 mm/yr of Slip within the Makassar Strait with current elastic strain accumulation. The tectonic boundary between North Sula and Manado blocks is the Gorontalo Fault, moving right laterally at about 11 mm/yr and accumulating elastic strain. The 42 mm/yr relative motion between North Sula and Makassar blocks is accommodated on the Palu?Koro left?lateral strike?Slip fault zone. The data also indicate a pull?apart structure in Palu area, where the fault shows a transtensive motion and may have a complex geometry involving several active strands. Sulawesi provides a primary example of how collision can be accommodated by crustal block rotation instead of mountain building.