Active tectonics of the Seattle fault and central Puget Sound, Washington—Implications for earthquake hazards

Johnson, Samuel Y.; Dadisman, Shawn V.; Childs, J. R.; Stanley, William D.

doi:10.1130/0016-7606(1999)111<1042:atotsf>2.3.co;2

Cited by 98 publications

(156 citation statements)

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“…Pratt et al, 1997). Reverse displacement on the Seattle fault has resulted in both subsidence of the Seattle basin north of the fault and uplift of the basement south of the fault (Johnson et al, 1994(Johnson et al, , 1999Pratt et al, 1997). Holocene seismicity and tsunamigenesis have been documented on the Seattle fault (e.g.…”

Section: Seattle Faultmentioning

confidence: 99%

“…7b), the fault location correlates with the gradient change, at a small distance east of the fault. Johnson et al (1999) identified a zone of active or potentially active north-trending strike-slip and normal faults, a few kilometers east of and parallel to the Coast Range Boundary fault, representing a portion of a regionally distributed shear zone along which the Washington Coast Range is moving northward relative to the eastern Puget Lowland and Cascade Range. Approximately 10 km east of the CRBF locations identified on profiles EF and GH, there is a near vertical line of earthquake locations that correlate with faults paralleling CRBF discussed by Johnson et al (1999).…”

Section: Coast Range Boundary Faultmentioning

confidence: 99%

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Constraining fault interpretation through tomographic velocity gradients: application to northern Cascadia

Ramachandran

2012

Solid Earth

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Abstract. Spatial gradients of tomographic velocities are seldom used in interpretation of subsurface fault structures. This study shows that spatial velocity gradients can be used effectively in identifying subsurface discontinuities in the horizontal and vertical directions. Three-dimensional velocity models constructed through tomographic inversion of active source and/or earthquake traveltime data are generally built from an initial 1-D velocity model that varies only with depth. Regularized tomographic inversion algorithms impose constraints on the roughness of the model that help to stabilize the inversion process. Final velocity models obtained from regularized tomographic inversions have smooth three-dimensional structures that are required by the data. Final velocity models are usually analyzed and interpreted either as a perturbation velocity model or as an absolute velocity model. Compared to perturbation velocity model, absolute velocity models have an advantage of providing constraints on lithology. Both velocity models lack the ability to provide sharp constraints on subsurface faults. An interpretational approach utilizing spatial velocity gradients applied to northern Cascadia shows that subsurface faults that are not clearly interpretable from velocity model plots can be identified by sharp contrasts in velocity gradient plots. This interpretation resulted in inferring the locations of the Tacoma, Seattle, Southern Whidbey Island, and Darrington Devil's Mountain faults much more clearly. The Coast Range Boundary fault, previously hypothesized on the basis of sedimentological and tectonic observations, is inferred clearly from the gradient plots. Many of the fault locations imaged from gradient data correlate with earthquake hypocenters, indicating their seismogenic nature.

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Section: Seattle Faultmentioning

confidence: 99%

Section: Coast Range Boundary Faultmentioning

confidence: 99%

Constraining fault interpretation through tomographic velocity gradients: application to northern Cascadia

Ramachandran

2012

Solid Earth

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“…The most prominent of the faults identified in the Puget Lowland is the east-west trending, south-dipping Seattle Fault (Pratt et al, 1997;Johnson et al, 1999a). This fault was associated with a M Ͼ 7 event ca.…”

Section: Geological Setting and Recent Geophysical Studiesmentioning

confidence: 99%

Characterization of Active Faulting Beneath the Strait of Georgia, British Columbia

Cassidy¹,

Rogers²,

Waldhauser³

2000

Bulletin of the Seismological Society of America

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Southwestern British Columbia and northwestern Washington State are subject to megathrust earthquakes, deep intraslab events, and earthquakes in the continental crust. Of the three types of earthquakes, the most poorly understood are the crustal events. Despite a high level of seismicity, there is no obvious correlation between the historical crustal earthquakes and the mapped surface faults of the region. On 24 June 1997, a M L ‫ס‬ 4.6 earthquake occurred 3-4 km beneath the Strait of Georgia, 30 km to the west of Vancouver, British Columbia. This well-recorded earthquake was preceded by 11 days by a felt foreshock (M L ‫ס‬ 3.4) and was followed by numerous small aftershocks. This earthquake sequence occurred in one of the few regions of persistent shallow seismic activity in southwestern British Columbia, thus providing an ideal opportunity to attempt to characterize an active near-surface fault. We have computed focal mechanisms and utilized a waveform cross-correlation and joint hypocentral determination routine to obtain accurate relative hypocenters of the mainshock, foreshock, and 53 small aftershocks in an attempt to image the active fault and the extent of rupture associated with this earthquake sequence. Both Pnodal and CMT focal mechanisms show thrust faulting for the mainshock and the foreshock. The relocated hypocenters delineate a north-dipping plane at 2-4 km depth, dipping at 53Њ, in good agreement with the focal mechanism nodal plane dipping to the north at 47Њ. The rupture area is estimated to be a 1.3-km-diameter circular area, comparable to that estimated using a Brune rupture model with the estimated seismic moment of 3.17 ‫ן‬ 10 15 N m and the stress drop of 45 bars. The temporal sequence indicates a downdip migration of the seismicity along the fault plane. The results of this study provide the first unambiguous evidence for the orientation and sense of motion for active faulting in the Georgia Strait area of British Columbia.

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“…Inferred fault strands (dotted lines) are shown for the Seattle fault zone , along the Hood Canal (Brocher et al, 2001), and the Coast Range Boundary faults (CRBF) (Johnson et al, 1999).…”

Section: Tacoma Fault Zone Geophysicsmentioning

confidence: 99%

“…The Seattle fault zone bounds the northern side of the Seattle uplift, and the Tacoma fault zone bounds the southern flank. Several investigators recently discussed the geometry of the Seattle fault zone based on these and other data (Johnson et al, 1994, 1999Pratt, 1997Blakely et al, 2002;ten Brink et al, 2002), where several kilometers of structural relief on the top of the Crescent Formation volcanics is inferred ( Johnson et al, 1999;Brocher et al, 2001). …”

Section: Introductionmentioning

confidence: 99%

The Catfish Lake Scarp, Allyn, Washington: Preliminary field data and implications for earthquake hazards posed by the Tacoma fault

Sherrod¹,

Nelson²,

Kelsey³

et al. 2004

Open-File Report

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Active tectonics of the Seattle fault and central Puget Sound, Washington—Implications for earthquake hazards

Cited by 98 publications

References 0 publications

Constraining fault interpretation through tomographic velocity gradients: application to northern Cascadia

Constraining fault interpretation through tomographic velocity gradients: application to northern Cascadia

Characterization of Active Faulting Beneath the Strait of Georgia, British Columbia

The Catfish Lake Scarp, Allyn, Washington: Preliminary field data and implications for earthquake hazards posed by the Tacoma fault

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