A new high-resolution radiocarbon Bayesian age model of the Holocene and Late Pleistocene from core MD02-2494 and others, Effingham Inlet, British Columbia, Canada; with an application to the paleoseismic event chronology of the Cascadia Subduction Zone

Annually laminated sediments from the anoxic inner basin of Effingham Inlet, Pacific coast of Vancouver Island, British Columbia, Canada, yield a high-resolution 42 m paleoenvironmental record, from the present to about 14 ka 14C BP (17 ka cal BP). A new age model, based on 68 radiocarbon dates from twigs and small plant material, from the 40 m core MD02-2494 and 2 m freeze cores from the surface, is anchored by the Mazama Ash and varve counting. A Poisson-process sedimentation model is used, applying a new method to determine the Poisson k value, giving a realistic age model compatible with the multi-proxy core data. Twenty-one “seismites”, which are lithofacies in the Effingham cores that may be representative of seismically triggered mass-wasting events, are identified and dated precisely, then compared with the chronology of the deep-sea turbidite record farther south in the Cascadia Subduction Zone (CSZ), to determine if regional sediment disturbances can be identified. With 16 proposed correlations, Effingham seismite ages are 169 ± 206 years older than turbidite ages estimated largely by radiocarbon analysis of foraminifera in hemipelagic deposits.

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Summary of Coastal Geologic Evidence for past Great Earthquakes at the Cascadia Subduction Zone

Earthquake Spectra ◽

10.1193/1.1585800 ◽

1995 ◽

Vol 11 (1) ◽

pp. 1-18 ◽

Cited By ~ 163

Author(s):

Brian F. Atwater ◽

Alan R. Nelson ◽

John J. Clague ◽

Gary A. Carver ◽

David K. Yamaguchi ◽

...

Keyword(s):

British Columbia ◽

North America ◽

Subduction Zone ◽

Forest Soils ◽

Pacific Coast ◽

Cascadia Subduction Zone ◽

Level Change ◽

The Past ◽

The Pacific ◽

Juan De Fuca

Earthquakes in the past few thousand years have left signs of land-level change, tsunamis, and shaking along the Pacific coast at the Cascadia subduction zone. Sudden lowering of land accounts for many of the buried marsh and forest soils at estuaries between southern British Columbia and northern California. Sand layers on some of these soils imply that tsunamis were triggered by some of the events that lowered the land. Liquefaction features show that inland shaking accompanied sudden coastal subsidence at the Washington-Oregon border about 300 years ago. The combined evidence for subsidence, tsunamis, and shaking shows that earthquakes of magnitude 8 or larger have occurred on the boundary between the overriding North America plate and the downgoing Juan de Fuca and Gorda plates. Intervals between the earthquakes are poorly known because of uncertainties about the number and ages of the earthquakes. Current estimates for individual intervals at specific coastal sites range from a few centuries to about one thousand years.

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Viscosity of the asthenosphere from glacial isostatic adjustment and subduction dynamics at the northern Cascadia subduction zone, British Columbia, Canada

Journal of Geophysical Research Atmospheres ◽

10.1029/2008jb006077 ◽

2009 ◽

Vol 114 (B4) ◽

Cited By ~ 38

Author(s):

Thomas S. James ◽

Evan J. Gowan ◽

Ikuko Wada ◽

Kelin Wang

Keyword(s):

British Columbia ◽

Subduction Zone ◽

Cascadia Subduction Zone ◽

Glacial Isostatic Adjustment ◽

Isostatic Adjustment

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Upper mantle structure of the northern Cascadia subduction zone

Canadian Journal of Earth Sciences ◽

10.1139/e95-001 ◽

1995 ◽

Vol 32 (1) ◽

pp. 1-12 ◽

Cited By ~ 60

Author(s):

M. G. Bostock ◽

J. C. Vandecar

Keyword(s):

British Columbia ◽

Subduction Zone ◽

Upper Mantle ◽

Puget Sound ◽

Cascadia Subduction Zone ◽

Mantle Structure ◽

Data Set ◽

Juan De Fuca Plate ◽

Upper Mantle Structure ◽

Juan De Fuca

Previous knowledge of the structure of the Cascadia subduction zone north of the Canada–United States border has been derived from a variety of geophysical studies that accurately delineated the downgoing Juan de Fuca plate from the offshore deformation front to depths of ~50–60 km beneath south-central Vancouver Island and the Georgia Strait. Little is known, however, of the structure of the Cascadia subduction zone farther westward and to greater depths in the upper mantle. We have assembled a set of some 1100 teleseismic traveltimes from events recorded on the Western Canadian Telemetered Network to augment a previously existing data set recorded on the Washington Regional Seismograph Network. The composite data set is inverted for upper mantle structure below Washington, Oregon, and southwestern British Columbia. We analyze the new northern portion of the model between 48.5–50°N and 118–127°W, which provides the first images of the deep slab structure in this region. The model is parameterized using splines under tension over a dense grid of knots. The nonlinearity of the inverse problem is treated by iteratively performing three-dimensional ray tracing and linear inversion. Resolution tests performed with a synthetic slab model indicate that the deep structure is resolved by the data north to at least 50°N. The inversions are characterized by a quasi-planar, high-velocity body inferred to represent the thermal and compositional anomaly of the subducted Juan de Fuca plate. This body exhibits velocity deviations of up to 3% from the background reference model and extends to depths of at least 400–500 km. The depth contours of the slab in the upper mantle mimic those of the shallow slab by changing strike, in the latitude range 48.0–48.5°N, from north–south in Washington to northwest–southeast in southern British Columbia. This forces the development of two arch-type structures: a main arch observed in previous studies trending east–west over Puget Sound and a possible second arch extending northeasterly from the Georgia Strait into the British Columbia interior. A steepening of the deep slab dip from British Columbia south towards Puget Sound and complexity in the evolution of the arches in depth may be the result of a change in plate motions at 3.5 Ma associated with the detachment of the Explorer plate.

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Postglacial evolution of a Pacific coastal fjord in British Columbia, Canada: interactions of sea-level change, crustal response, and environmental fluctuations — results from MONA core MD02-2494This article is one of a series of papers published in this Special Issue on the theme Polar Climate Stability Network.

Canadian Journal of Earth Sciences ◽

10.1139/e08-042 ◽

2008 ◽

Vol 45 (11) ◽

pp. 1345-1362 ◽

Cited By ~ 23

Author(s):

Audrey Dallimore ◽

Randolph J. Enkin ◽

Reinhard Pienitz ◽

John R. Southon ◽

Judith Baker ◽

...

Keyword(s):

British Columbia ◽

Sea Level ◽

Radiocarbon Dates ◽

Polar Climate ◽

The Core ◽

Mantle Viscosity ◽

Climate Stability ◽

Viscosity Models ◽

New Information ◽

Effingham Inlet

The sedimentary record in a 40.9 m giant (Calypso) piston core (MD02-2494) raised from the inner basin within Effingham Inlet, British Columbia, Canada, during the 2002 Marges Ouest Nord Américaines (MONA) campaign, spans from 14 360 14C years BP (17 300 calibrated calendar (cal.) years BP) to about nine centuries before present. The core archives changes in sedimentation and sea level immediately following deglaciation of the Late Wisconsin Fraser Glaciation, which peaked about 15 000 14C years BP. The presence of the Mazama Ash in the core anchors a detailed chronology based on 49 radiocarbon dates and seven Pleistocene paleomagnetic secular variation correlations. Diatom assemblages identify a marine–freshwater–marine transition in the basin, which occurred 11 630 14C years BP (13 500 cal. years BP). At this time, a bedrock sill, presently at 46 m depth, was briefly exposed as sea level fell and then rose again during isostatic crustal adjustments. These data constrain a new sea-level curve for the outer coast of Vancouver Island covering the past 12 000 14C years BP (14 000 cal. years BP), providing new information on the nature of deglaciation along the west coast of Canada and informing interpretations of regional paleoceanographic records and mantle viscosity models.

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