Preliminary geologic interpretation of a seismic reflection profile across the Queen Charlotte Island fault system, Dixon Entrance, Canada-United States

Snavely, Parke Detweiler; Wagner, Holly Clyde; Tompkins, Donald H.; Tiffin, D. L.

doi:10.3133/ofr81299

Cited by 7 publications

(6 citation statements)

References 4 publications

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“…Thus, we interpret that much of the lowermost package was deposited between 13 and 6 Ma, with deformation and growth strata initiating sometime after 6 Ma. This interpretation is consistent with that of Snavely et al (1981), stating that the SEAK1 unconformity represents the Miocene-Pliocene unconformity (∼5:3 Ma).…”

Section: Crustal Flexuresupporting

confidence: 76%

“…6, inset), suggesting that extensional deformation is no longer active today. Without deep cores in the area, it is impossible to date mapped surfaces and faults, though other studies have interpreted the SEAK1 horizon as a Miocene-Pliocene unconformity, identifiable by truncating reflectors and a change in interval velocity (Snavely et al, 1981;Scheidhauer, 1997;Tréhu et al, 2015).…”

Section: Faultingmentioning

confidence: 99%

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Basement and Regional Structure Along Strike of the Queen Charlotte Fault in the Context of Modern and Historical Earthquake Ruptures

Walton

Gulick

Haeussler

et al. 2015

Bulletin of the Seismological Society of America

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The Queen Charlotte fault (QCF) is a dextral transform system located offshore of southeastern Alaska and western Canada, accommodating ∼4:4 cm=yr of relative motion between the Pacific and North American plates. Oblique convergence along the fault increases southward, and how this convergence is accommodated is still debated. Using seismic reflection data, we interpret offshore basement structure, faulting, and stratigraphy to provide a geological context for two recent earthquakes, an M w 7.5 strike-slip event near Craig, Alaska, and an M w 7.8 thrust event near Haida Gwaii, Canada. We map downwarped Pacific oceanic crust near 54°N, between the two rupture zones. Observed downwarping decreases north and south of 54°N, parallel to the strike of the QCF. Bending of the Pacific plate here may have initiated with increased convergence rates due to a plate motion change at ∼6 Ma. Tectonic reconstruction implies convergence-driven Pacific plate flexure, beginning at 6 Ma south of a 10°bend the QCF (which is currently at 53.2°N) and lasting until the plate translated past the bend by ∼2 Ma. Normal-faulted approximately late Miocene sediment above the deep flexural depression at 54°N, topped by relatively undeformed Pleistocene and younger sediment, supports this model. Aftershocks of the Haida Gwaii event indicate a normal-faulting stress regime, suggesting present-day plate flexure and underthrusting, which is also consistent with reconstruction of past conditions. We thus favor a Pacific plate underthrusting model to initiate flexure and accommodation space for sediment loading. In addition, mapped structures indicate two possible fault segment boundaries along the QCF at 53.2°N and at 56°N.

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Section: Crustal Flexuresupporting

confidence: 76%

Section: Faultingmentioning

confidence: 99%

Basement and Regional Structure Along Strike of the Queen Charlotte Fault in the Context of Modern and Historical Earthquake Ruptures

Walton

Gulick

Haeussler

et al. 2015

Bulletin of the Seismological Society of America

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show abstract

“…Deformation must be younger than about 15 Ma, the age of the underlying oceanic crust. The Miocene-Pliocene unconformity (5.3 Ma), labeled U in Figures 8 and 9, can be tentatively identified west of the terrace based on an abrupt change in seismic interval velocity and the presence of truncated or bright reflectors (Snavely et al, 1981;Scheidhauer, 1997;Walton et al, 2015). This unconformity is regionally observed and may be associated with a period of erosion or nondeposition coinciding with the onset of transpression at 5-6 Ma.…”

Section: Constraints On Timingmentioning

confidence: 99%

“…Because of the very strong seafloor multiples resulting from a reflection coefficient of ∼0:5 along most of the profiles (Scheidhauer, 1997), the first multiple and underlying data were muted prior to migration. The R/V Lee data (see Data and Resources) were 24-fold with a common midpoint spacing of 50 m, and total source volume was 22 L (1326 in 3 ) (Snavely et al, 1981;Rohr et al, 1992). The R/V Lee data were migrated using a frequencywavenumber algorithm and a velocity of 1500 m=s for this publication.…”

Section: Multichannel Seismic Reflection Datamentioning

confidence: 99%

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An Abrupt Transition in the Mechanical Response of the Upper Crust to Transpression along the Queen Charlotte Fault

Tréhu¹,

Scheidhauer²,

Rohr³

et al. 2015

Bulletin of the Seismological Society of America

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The Queen Charlotte Fault (QCF) is a major strike-slip fault that forms the boundary between the Pacific and North American plates from 51°to 58°N. Near 53.2°N, the angle of oblique convergence predicted by the Mid-Ocean Ridge VELocity (MORVEL) interplate pole of rotation decreases from > 15°in the south to < 15°in the north. South of 53.2°N, the convergent component of plate motion results in the formation of a 40 km wide terrace on the Pacific plate west of QCF and earthquakes with thrust mechanisms (including the 2012 Haida Gwaii earthquake sequence) are observed. North of 53.2°N, in the primary rupture zone of the M 8.1 strike-slip earthquake of 1949, the linear terrace disappears, and topography of the continental slope west of the QCF is characterized by a complex pattern of ridges and basins that trend obliquely to the primary trace of the QCF. Deformation within the Pacific plate appears to occur primarily through strike-slip faulting with a minor thrust component on secondary synthetic faults. The orientations of these secondary faults, as determined from seismic reflection and bathymetric data, are consistent with the reactivation of faults originally formed as ridge-parallel normal faults and as thrust faults formed parallel to the QCF south of the bend at 53.2°N and subsequently translated to the north. We suggest that an oblique convergence angle of 15°represents a critical threshold separating distinct crustal responses to transpression. This result is consistent with theoretical and analog strain models of transpressive plate boundaries. The sharpness of this transition along the QCF, in contrast to purely continental transform boundaries, may be facilitated by the relatively simple structure of oceanic crust and the presence of pre-existing, optimally oriented faults in the young Pacific plate.

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Transpression between two warm mafic plates: The Queen Charlotte Fault revisited

Rohr¹,

Scheidhauer²,

Tréhu³

2000

J. Geophys. Res.

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Preliminary geologic interpretation of a seismic reflection profile across the Queen Charlotte Island fault system, Dixon Entrance, Canada-United States

Cited by 7 publications

References 4 publications

Basement and Regional Structure Along Strike of the Queen Charlotte Fault in the Context of Modern and Historical Earthquake Ruptures

Basement and Regional Structure Along Strike of the Queen Charlotte Fault in the Context of Modern and Historical Earthquake Ruptures

An Abrupt Transition in the Mechanical Response of the Upper Crust to Transpression along the Queen Charlotte Fault

Transpression between two warm mafic plates: The Queen Charlotte Fault revisited

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