Field Studies Target 2012 Haida Gwaii Earthquake

James, T. S.; Rogers, Garry C.; Cassidy, John F.; Dragert, H.; Hyndman, R. D.; Leonard, Lucinda J.; Nykolaishen, L.; Riedel, Michael; Schmidt, Michaël; Wang, Kelin

doi:10.1002/2013eo220002

Cited by 27 publications

(18 citation statements)

References 3 publications

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“…We infer a gently dipping Pacific plate in the region of the Haida Gwaii event. The Haida Gwaii earthquake fits in well with this observation, as the mainshock ruptured a fault dipping 18.5°to the east at 14 km depth beneath the seafloor of the QCT (James et al, 2013;Lay et al, 2013;USGS, see Data and Resources). In addition, several recent studies based on seismicity, GPS observations of coseismic and postseismic motion, and thermal modeling Kao et al, 2015;Nykolaishen et al, 2015;Wang et al, 2015) support the Haida Gwaii event as a shallow megathrust on the Pacific-North American plate interface near the QCF.…”

Section: Faultingsupporting

confidence: 67%

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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: Faultingsupporting

confidence: 67%

“…1). This earthquake (the Haida Gwaii earthquake) occurred on a thrust fault with some oblique slip, striking north-northwest ∼320°and dipping ∼18:5°to the east; it ruptured ∼150 km of a fault at 14 km depth, with an average ∼3:3 m of slip (James et al, 2013;Lay et al, 2013;U.S. Geological Survey [USGS], see Data and Resources).…”

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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“…Following the 2012 Haida Gwaii earthquake, Szeliga (2013) argued that the northern end of subduction along the Cascadia margin may need to be redefined, as the primarily strike-slip Queen Charlotte Fault has a smaller component of convergence. Early GPS position data collected during that earthquake indicate a meter of coseismic displacement toward the rupture, followed by more than 1 mm d À1 of postseismic strain (James et al, 2013). The north end of the Queen Charlotte fault is affected by the motion of the Yakutat Block (see below) that causes the Queen Charlotte fault to rotate clockwise (e.g.…”

Section: Regional Tectonic Regimementioning

confidence: 99%

“…Although recent studies into the 2012 Haida Gwaii earthquake have documented a component of convergence along the predominantly strike-slip Queen Charlotte Fault (James et al, 2013;Lay et al, 2013;Szeliga, 2013), it is not known whether this has had a significant effect on RSL fluctuations since the LGM.…”

Section: Outer Islands-north Coastmentioning

confidence: 99%

Post-glacial sea-level change along the Pacific coast of North America

Shugar

Walker

Lian

et al. 2014

Quaternary Science Reviews

128

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a b s t r a c tSea-level history since the Last Glacial Maximum on the Pacific margin of North America is complex and heterogeneous owing to regional differences in crustal deformation (neotectonics), changes in global ocean volumes (eustasy) and the depression and rebound of the Earth's crust in response to ice sheets on land (isostasy). At the Last Glacial Maximum, the Cordilleran Ice Sheet depressed the crust over which it formed and created a raised forebulge along peripheral areas offshore. This, combined with different tectonic settings along the coast, resulted in divergent relative sea-level responses during the Holocene. For example, sea level was up to 200 m higher than present in the lower Fraser Valley region of southwest British Columbia, due largely to isostatic depression. At the same time, sea level was 150 m lower than present in Haida Gwaii, on the northern coast of British Columbia, due to the combined effects of the forebulge raising the land and lower eustatic sea level. A forebulge also developed in parts of southeast Alaska resulting in post-glacial sea levels at least 122 m lower than present and possibly as low as 165 m. On the coasts of Washington and Oregon, as well as south-central Alaska, neotectonics and eustasy seem to have played larger roles than isostatic adjustments in controlling relative sea-level changes.

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“…1). With moment magnitude (M w ) 7.8, the mainshock of this earthquake sequence is deemed the second largest seismic event in Canada since a modern seismograph network was established (James et al, 2013). It created a tsunami with waves as high as 13 m and runup exceeding 3 m at sites spanning ∼200 km of the local coastline (Leonard and Bednarski, 2014).…”

Section: Introductionmentioning

confidence: 99%

Source Characteristics of the 2012 Haida Gwaii Earthquake Sequence

Kao

Shan

Farahbod

2015

Bulletin of the Seismological Society of America

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All the significant (M L ≥ 4) events in the 2012 Haida Gwaii earthquake sequence are systematically relocated, and their moment tensor solutions are determined from waveform inversion. The focal mechanism of the mainshock shows lowangle thrust faulting along a shallowly dipping plane with a strike parallel to the Queen Charlotte fault (QCF), consistent with the inference of Pacific plate underthrusting beneath the overriding North American plate. The epicenter of the mainshock is located ∼5 km landward (northeast) of the surface trace of the QCF, suggesting the nucleation of the rupture was near the bottom of the seismogenic (locked) interface. Significant aftershocks appear to cluster on the periphery of the main rupture zone with most events located immediately seaward of the deformation front. The majority of these events show normal-faulting mechanisms that are probably associated with the bending stress within the Pacific plate near the deformation front. Several normal and strike-slip events at greater depths within the subducted Pacific slab show a consistent pattern of T-axis in the down-dip direction, implying the subducted plate is under a stress regime of down-dip extension. Only a few strike-slip events were observed along or near the QCF. The limited size and distribution of these events suggest that most of the elastic strain accumulated along the QCF was not released during the 2012 Haida Gwaii sequence. Major strike-slip earthquakes are likely to occur along the southernmost part of the QCF system in the future.

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Field Studies Target 2012 Haida Gwaii Earthquake

Cited by 27 publications

References 3 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

Post-glacial sea-level change along the Pacific coast of North America

Source Characteristics of the 2012 Haida Gwaii Earthquake Sequence

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