Plate Boundary Adjustments of the Southernmost Queen Charlotte Fault

Rohr, Kristin M. M.

doi:10.1785/0120140162

Cited by 29 publications

(74 citation statements)

References 52 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…South of 56°N, areas immediately adjacent to the QCF are characterized by negative gravity anomalies. These gravity lows vanish at the southernmost QCF near the Explorer triple junction, where basement rock is very young, shallow, and not yet covered with sediment (Rohr, 2015).…”

Section: Gravity and Magneticsmentioning

confidence: 99%

“…The 100 m resolution UNCLOS data were merged with ETOPO1 1 arc-min global relief data (Amante and Eakins, 2009; see also Data and Resources) and used primarily as a background map for reference. The southernmost QCF has new, high-resolution multibeam coverage and is discussed in a study by Barrie et al (2013) and Rohr (2015).…”

Section: Datamentioning

confidence: 99%

“…This is constrained by only one seismic line (Fig. 8), but other studies have inferred crustal flexure here by looking at the bathymetry of the Queen Charlotte Trough (e.g., Chase and Tiffin, 1972), low-penetration seismic data (Davis and Seemann, 1981), and negative gravity anomalies (Rohr, 2015). South of this crustal deepening near Haida Gwaii, the basement shallows southward toward the Tuzo Wilson seamounts ∼51:5°N (see transect F-7-89-EG_58, Fig.…”

Section: Pacific Basementmentioning

confidence: 99%

“…The southern boundary of the QCF is marked by the complex Pacific-North American-Explorer triple junction off the coast of southern British Columbia ( Fig. 1; Rohr and Furlong, 1995;Rohr, 2015). South of 53.2°N, near Haida Gwaii, the strike of the QCF is 328°, ∼10°less than the northern QCF, creating oblique convergence between the plates and a structural regime similar to a restraining bend along the southern QCF ( Fig.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

View full text Add to dashboard Cite

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.

show abstract

Section: Gravity and Magneticsmentioning

confidence: 99%

Section: Datamentioning

confidence: 99%

Section: Pacific Basementmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

View full text Add to dashboard Cite

show abstract

“…South of 52°N, the margin morphology is affected by northward propagation of the Revere-Dellwood fault ( Fig. 2a, inset; Rohr, 2015). Seismicity (Hyndman and Ellis, 1981) and GLORIA sidescan data (Bruns et al, 1992) indicate that the scarp on the northeast side of the QCT corresponds to the primary trace of the QCF.…”

Section: Morphology Of the Queen Charlotte Terracementioning

confidence: 99%

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

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Precise relative locations for earthquakes in the northeast Pacific region

2015

View full text Add to dashboard Cite

Double‐difference methods applied to cross‐correlation measured Rayleigh wave time shifts are an effective tool to improve epicentroid locations and relative origin time shifts in remote regions. We apply these methods to seismicity offshore of southwestern Canada and the U.S. Pacific Northwest, occurring along the boundaries of the Pacific and Juan de Fuca (including the Explorer Plate and Gorda Block) Plates. The Blanco, Mendocino, Revere‐Dellwood, Nootka, and Sovanco fracture zones host the majority of this seismicity, largely consisting of strike‐slip earthquakes. The Explorer, Juan de Fuca, and Gorda spreading ridges join these fracture zones and host normal faulting earthquakes. Our results show that at least the moderate‐magnitude activity clusters along fault strike, supporting suggestions of large variations in seismic coupling along oceanic transform faults. Our improved relative locations corroborate earlier interpretations of the internal deformation in the Explorer and Gorda Plates. North of the Explorer Plate, improved locations support models that propose northern extension of the Revere‐Dellwood fault. Relocations also support interpretations that favor multiple parallel active faults along the Blanco Transform Fault Zone. Seismicity of the western half of the Blanco appears more scattered and less collinear than the eastern half, possibly related to fault maturity. We use azimuthal variations in the Rayleigh wave cross‐correlation amplitude to detect and model rupture directivity for a moderate size earthquake along the eastern Blanco Fault. The observations constrain the seismogenic zone geometry and suggest a relatively narrow seismogenic zone width of 2 to 4 km.

show abstract

Plate Boundary Adjustments of the Southernmost Queen Charlotte Fault

Cited by 29 publications

References 52 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

Precise relative locations for earthquakes in the northeast Pacific region

Contact Info

Product

Resources

About