The Yakutat terrane: Dramatic change in crustal thickness across the Transition fault, Alaska

Christeson, G. L.; Gulick, Sean P. S.; Avendonk, H. J. Van; Worthington, L. L.; Reece, R.; Pavlis, Terry L.

doi:10.1130/g31170.1

Cited by 140 publications

(217 citation statements)

References 26 publications

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“…This gentle southwest dip of the top of the seismogenic zone has been estimated from relatively low-resolution tomography data [Eberhart-Phillips et al, 2006], but here we show with much higher resolution that the megathrust is indeed gradual and no large-scale midcrustal step is present at the Yakutat terrane boundary. This gradual transition contrasts with the Yakutat/Pacific plate boundary along the Transition fault beneath the eastern Gulf of Alaska, where an abrupt change in crustal thickness is observed [Christeson et al, 2010] [31] Between positions 30 km and 90 km on the TACT profile, we observe additional reflectors below the megathrust that form a lens-shaped zone of reflective rocks ( Figure 5). This region is coincident with the prominent magnetic high [Griscom and Sauer, 1990;Figure 1] and is consistent with a low seismic velocity (6.4-6.6 km/s) zone beneath the megathrust in the Brocher et al [1994] refraction model ( Figure 5).…”

Section: Deep Splay Fault Geometry From Seismic Imagesmentioning

confidence: 90%

Megathrust splay faults at the focus of the Prince William Sound asperity, Alaska

et al. 2013

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[1] High-resolution sparker and crustal-scale air gun seismic reflection data, coupled with repeat bathymetric surveys, document a region of repeated coseismic uplift on the portion of the Alaska subduction zone that ruptured in 1964. This area defines the western limit of Prince William Sound. Differencing of vintage and modern bathymetric surveys shows that the region of greatest uplift related to the 1964 Great Alaska earthquake was focused along a series of subparallel faults beneath Prince William Sound and the adjacent Gulf of Alaska shelf. Bathymetric differencing indicates that 12 m of coseismic uplift occurred along two faults that reached the seafloor as submarine terraces on the Cape Cleare bank southwest of Montague Island. Sparker seismic reflection data provide cumulative Holocene slip estimates as high as 9 mm/yr along a series of splay thrust faults within both the inner wedge and transition zone of the accretionary prism. Crustal seismic data show that these megathrust splay faults root separately into the subduction zone décollement. Splay fault divergence from this megathrust correlates with changes in midcrustal seismic velocity and magnetic susceptibility values, best explained by duplexing of the subducted Yakutat terrane rocks above Pacific plate rocks along the trailing edge of the Yakutat terrane. Although each splay fault is capable of independent motion, we conclude that the identified splay faults rupture in a similar pattern during successive megathrust earthquakes and that the region of greatest seismic coupling has remained consistent throughout the Holocene.

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Section: Deep Splay Fault Geometry From Seismic Imagesmentioning

confidence: 90%

Megathrust splay faults at the focus of the Prince William Sound asperity, Alaska

et al. 2013

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“…7) was generated at a ridge and is similar in age to the surrounding crust; despite this, we do not observe obvious flexure here. It is possible that the locally thicker and more buoyant crust of the Kodiak-Bowie seamounts may have resisted underthrusting and/or blocked propagation of flexure to the south (e.g., Christeson et al, 2010;Worthington et al, 2012), though more likely it is simply an overprinting of flexure due to higher topography. We are unable to effectively image and assess flexure around the seamounts with the existing data coverage, however.…”

Section: Crustal Flexurementioning

confidence: 99%

“…The junction of the Queen Charlotte, Fairweather, and Transition faults is located at the southeastern tip of the Yakutat block, an oceanic plateau and microplate ( Fig. 1; Gulick et al, 2007;Christeson et al, 2010). 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.…”

Section: Introductionmentioning

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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“…We define 'collision' in this case as highly coupled flat-slab subduction at the subduction margin. The Yakutat microplate is composed of crystalline crust that is 15 -30 km thick and is inferred to have an oceanic plateau origin (Christenson et al 2010;Worthington et al 2012). Based on tomographical studies, the Yakutat microplate is currently undergoing flat-slab subduction beneath the Chugach-Saint Elias Mountains, with a northern edge 500 km inboard of the subduction zone at a depth of about 100 km (Eberhart-Phillips et al 2006).…”

Section: Alaska Range Deformation In Response To the Yakutat Collisionmentioning

confidence: 99%

Persistent long-term (c.24 Ma) exhumation in the Eastern Alaska Range constrained by stacked thermochronology

Benowitz

Layer

VanLaningham

2013

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The Yakutat terrane: Dramatic change in crustal thickness across the Transition fault, Alaska

Cited by 140 publications

References 26 publications

Megathrust splay faults at the focus of the Prince William Sound asperity, Alaska

Megathrust splay faults at the focus of the Prince William Sound asperity, Alaska

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

Persistent long-term (c.24 Ma) exhumation in the Eastern Alaska Range constrained by stacked thermochronology

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