Fault Locking, Block Rotation and Crustal Deformation in the Pacific Northwest

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....

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Authors: McCaffrey, R., Qamar, A. I., King, R. W., Wells, R., Khazaradze, Giorgi, Williams, Ch. A., Stevens, C. W., Vollick, J. J., Zwick, P. C.
Format: article
Status:Published version
Publication Date:2007
Country:España
Institution:Universidad de Barcelona
Repository:Dipòsit Digital de la UB
OAI Identifier:oai:diposit.ub.edu:2445/163338
Online Access:https://hdl.handle.net/2445/163338
Access Level:Open access
Keyword:Geodinàmica
Terratrèmols
Sismologia
Tectònica
Geodynamics
Earthquakes
Seismology
Tectonics
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spelling Fault Locking, Block Rotation and Crustal Deformation in the Pacific NorthwestMcCaffrey, R.Qamar, A. I.King, R. W.Wells, R.Khazaradze, GiorgiWilliams, Ch. A.Stevens, C. W.Vollick, J. J.Zwick, P. C.GeodinàmicaTerratrèmolsSismologiaTectònicaGeodynamicsEarthquakesSeismologyTectonicsWe 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.Royal Astronomical Society2007info:eu-repo/semantics/articleinfo:eu-repo/semantics/publishedVersionapplication/pdfhttps://hdl.handle.net/2445/163338Articles publicats en revistes (Dinàmica de la Terra i l'Oceà)reponame:Dipòsit Digital de la UBinstname:Universidad de BarcelonaInglésReproducció del document publicat a: https://doi.org/10.1111/j.1365-246X.2007.03446.xGeophysical Journal International, 2007, vol. 69, num. 2, p. 787-792https://doi.org/10.1111/j.1365-246X.2007.03446.x(c) McCaffrey, R. et al., 2007info:eu-repo/semantics/openAccessoai:diposit.ub.edu:2445/1633382026-05-27T06:46:51Z
dc.title.none.fl_str_mv Fault Locking, Block Rotation and Crustal Deformation in the Pacific Northwest
title Fault Locking, Block Rotation and Crustal Deformation in the Pacific Northwest
spellingShingle Fault Locking, Block Rotation and Crustal Deformation in the Pacific Northwest
McCaffrey, R.
Geodinàmica
Terratrèmols
Sismologia
Tectònica
Geodynamics
Earthquakes
Seismology
Tectonics
title_short Fault Locking, Block Rotation and Crustal Deformation in the Pacific Northwest
title_full Fault Locking, Block Rotation and Crustal Deformation in the Pacific Northwest
title_fullStr Fault Locking, Block Rotation and Crustal Deformation in the Pacific Northwest
title_full_unstemmed Fault Locking, Block Rotation and Crustal Deformation in the Pacific Northwest
title_sort Fault Locking, Block Rotation and Crustal Deformation in the Pacific Northwest
dc.creator.none.fl_str_mv McCaffrey, R.
Qamar, A. I.
King, R. W.
Wells, R.
Khazaradze, Giorgi
Williams, Ch. A.
Stevens, C. W.
Vollick, J. J.
Zwick, P. C.
author McCaffrey, R.
author_facet McCaffrey, R.
Qamar, A. I.
King, R. W.
Wells, R.
Khazaradze, Giorgi
Williams, Ch. A.
Stevens, C. W.
Vollick, J. J.
Zwick, P. C.
author_role author
author2 Qamar, A. I.
King, R. W.
Wells, R.
Khazaradze, Giorgi
Williams, Ch. A.
Stevens, C. W.
Vollick, J. J.
Zwick, P. C.
author2_role author
author
author
author
author
author
author
author
dc.subject.none.fl_str_mv Geodinàmica
Terratrèmols
Sismologia
Tectònica
Geodynamics
Earthquakes
Seismology
Tectonics
topic Geodinàmica
Terratrèmols
Sismologia
Tectònica
Geodynamics
Earthquakes
Seismology
Tectonics
description 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.
publishDate 2007
dc.date.none.fl_str_mv 2007
dc.type.none.fl_str_mv info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
format article
status_str publishedVersion
dc.identifier.none.fl_str_mv https://hdl.handle.net/2445/163338
url https://hdl.handle.net/2445/163338
dc.language.none.fl_str_mv Inglés
language_invalid_str_mv Inglés
dc.relation.none.fl_str_mv Reproducció del document publicat a: https://doi.org/10.1111/j.1365-246X.2007.03446.x
Geophysical Journal International, 2007, vol. 69, num. 2, p. 787-792
https://doi.org/10.1111/j.1365-246X.2007.03446.x
dc.rights.none.fl_str_mv (c) McCaffrey, R. et al., 2007
info:eu-repo/semantics/openAccess
rights_invalid_str_mv (c) McCaffrey, R. et al., 2007
eu_rights_str_mv openAccess
dc.format.none.fl_str_mv application/pdf
dc.publisher.none.fl_str_mv Royal Astronomical Society
publisher.none.fl_str_mv Royal Astronomical Society
dc.source.none.fl_str_mv Articles publicats en revistes (Dinàmica de la Terra i l'Oceà)
reponame:Dipòsit Digital de la UB
instname:Universidad de Barcelona
instname_str Universidad de Barcelona
reponame_str Dipòsit Digital de la UB
collection Dipòsit Digital de la UB
repository.name.fl_str_mv
repository.mail.fl_str_mv
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score 15,300719

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