Multi-channel seismic reflection survey over the northern Queen Charlotte fault

Scheidhauer, M.; Tréhu, A. M.; Rohr, Kristin M. M.

doi:10.4095/210903

Cited by 6 publications

(13 citation statements)

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“…Line EW1262 is shown at larger scale in Figure 8, with the two-way travel time axis converted to depth beneath the sea surface using interval velocities derived from smoothed stacking velocities (Scheidhauer, 1997;Scheidhauer et al, 1999). Line BC951 (Bruns and Carlson, 1987), 30 km to the north, and USGS5, 10 km to the south, show similar features.…”

Section: Structural Observations and Interpretationsmentioning

confidence: 80%

“…Processing details for the EW9412 data are given by Scheidhauer (1997) and Scheidhauer et al (1999) and included sorting into 60-fold data with a common midpoint spacing of 12.5 m, band-pass filtering (10-60 Hz), velocity analysis at 1.25 km intervals, stacking, finite-difference migration, and depth conversion. An example of stacking velocities for line 1262 is shown in Figure 7.…”

Section: Multichannel Seismic Reflection Datamentioning

confidence: 99%

“…This structure is influencing, and is influenced by, seafloor sedimentation and erosion , as the ridge formed by fault zone A deflects the northern branch of the Mukluk channel to the south and the channel erodes the eastern flank of the ridge. These processes are indicated by high seafloor reflectivity and the intersection of shallow For the EW9412 lines (Scheidhauer et al, 1999;Rohr et al, 2000), smoothed interval velocities derived from stack velocities were used for migration. Because no velocity information was available for the USGS profiles, these were migrated using a constant velocity appropriate for the water column, which adequately corrects for the effects of rough seafloor and very shallow subsurface structure but is not adequate to image deeper structural details.…”

Section: Structural Observations and Interpretationsmentioning

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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Section: Structural Observations and Interpretationsmentioning

confidence: 80%

Section: Multichannel Seismic Reflection Datamentioning

confidence: 99%

Section: Structural Observations and Interpretationsmentioning

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 survey was collected aboard the R/V Maurice Ewing in 1994. Processing was completed by M. Scheidhauer (Scheidhauer, 1997;Scheidhauer et al, 1999). This survey was important for interpretation of faults and basement structure in the area, and examples of the EW9412 profiles can be seen in Rohr et al (2000) and Tréhu et al (2015).…”

Section: Datamentioning

confidence: 99%

“…Academic survey EW9412, shot as a part of the AC-CRETE project (e.g., Scheidhauer et al, 1999; see also Data and Resources), is one of the better-quality marine seismic datasets crossing the QCF, with five 2D seismic reflection lines covering the area just north of Haida Gwaii at the Dixon Entrance (Fig. 2).…”

Section: Datamentioning

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

Rohr¹,

Scheidhauer²,

Tréhu³

2000

J. Geophys. Res.

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Multi-channel seismic reflection survey over the northern Queen Charlotte fault

Cited by 6 publications

References 0 publications

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

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

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

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

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