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

1995 ◽  
Vol 11 (1) ◽  
pp. 1-18 ◽  
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.

Late Pleistocene stratigraphy of south-central British Columbia

1978 ◽  
Vol 15 (6) ◽  
pp. 971-980 ◽  
Author(s):  
Robert J. Fulton ◽  
Geoffrey W. Smith
Keyword(s):  
British Columbia ◽  
North America ◽  
Great Lakes ◽  
Late Pleistocene ◽  
Pacific Coast ◽  
Coastal Regions ◽  
South Central ◽  
The Pacific ◽  
Valley Area ◽  
Coast Region

The late Pleistocene deposits of south-central British Columbia record two major glacial and two major nonglacial periods of deposition. The oldest recognized Pleistocene deposits, called Westwold Sediments, were deposited during a nonglacial interval more than 60 000 years ago. Little information is available on the climate of this period, but permafrost may have been present at one time during final stages of deposition of Westwold Sediments. The latter part of this nonglacial period is probably correlative with the early Wisconsin Substage of the Great Lakes – St. Lawrence Valley area. However, deposition of the Westwold Sediments may have begun during the Sangamon Interglacial.Okanagan Centre Drift is the name applied to sediments deposited during the glaciation that followed deposition of Westwold Sediments. Okanagan Centre Drift is known to be older than 43 800 years BP and probably is older than 51 000. It is considered to correlate with an early Wisconsin glacial period.Bessette Sediments were deposited during the last major nonglacial period, which in south-central British Columbia persisted from at least 43 800 years BP (possibly more than 51 000) to about 19 000 years BP. This episode corresponds to Olympia Interglaciation of the Pacific Coast region and the mid-Wisconsin Substage of the Great Lakes – St. Lawrence Valley area. During parts of Olympia Interglaciation the climate was probably as warm as the present-day climate in the interior of British Columbia. Information from coastal regions indicates that there may have been periods of cooler and moister climate.Kamloops Lake Drift was deposited during the last major glaciation of south-central British Columbia. Ice occupied lowland areas from approximately 19 000 to 10 000 years BP. This period corresponds approximately to the Fraser Glaciation of the Pacific Coast region and the late Wisconsin Substage of central and eastern parts of North America.

A New Species of Bradyidius (Copepoda: Calanoida) from the Pacific Coast of North America

1966 ◽  
Vol 23 (6) ◽  
pp. 805-811 ◽  
Author(s):  
Tai Soo Park
Keyword(s):  
British Columbia ◽  
New Species ◽  
North America ◽  
Pacific Coast ◽  
Vancouver Island ◽  
Saanich Inlet ◽  
The Pacific ◽  
A New Species

A new species Bradyidius saanichi from Saanich Inlet, Vancouver Island, British Columbia, Canada, is described and illustrated in detail. This species is closely related to B. pacificus (Brodsky, 1950) among the six previously known species in the genus, but can be readily distinguished from the latter by the strongly divergent rostral rami in addition to some other differences.

Upper mantle structure of the northern Cascadia subduction zone

1995 ◽  
Vol 32 (1) ◽  
pp. 1-12 ◽  
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.

An assessment of the megathrust earthquake potential of the Cascadia subduction zone

1988 ◽  
Vol 25 (6) ◽  
pp. 844-852 ◽  
Author(s):  
Garry C. Rogers
Keyword(s):  
United States ◽  
Subduction Zone ◽  
Subduction Zones ◽  
Oceanic Lithosphere ◽  
The United States ◽  
Cascadia Subduction Zone ◽  
The South ◽  
The North ◽  
The Pacific ◽  
Juan De Fuca

The active tectonic setting of the southwest coast of Canada and the Pacific northwest coast of the United states is dominated by the Cascadia subduction zone. The zone can be divided into four segments where oceanic lithosphere is converging independently with the North American plate: the Winona and the Explorer segments in the north, the larger Juan de Fuca segment that extends into both Canada and the United States, and the Gorda segment in the south. The oceanic lithosphere entering the Cascadia subduction zone in all segments is extremely young, less than 10 Ma. Of the other six zones around the Pacific where young (< 20 Ma) lithosphere is being subducted, five have had major thrust earthquakes (megathrust events) on the subduction interface in historic time. An estimation based on potential area of rupture gives maximum possible earthquake magnitudes along the Cascadia subducting margin of 8.2 for the Winona segment, 8.5 for the Explorer segment, 9.1 for the Juan de Fuca segment, and 8.3 for the South Gorda segment. Repeat times for maximum earthquakes, based on the ratios of seismic slip to total slip observed in other subduction zones, are predicted to be up to several hundred years for each segment, well beyond recorded history of the west coast, which began about 1800. Thus the lack of historical seismicity information provides a few constraints on the assessment of the seismic potential of the subduction zone.

Parasites of yellowtail rockfish, Sebastes flavidus (Ayres, 1862) (Pisces: Teleostei), from the Pacific coast of North America as potential biological tags for stock identification

1992 ◽  
Vol 70 (6) ◽  
pp. 1086-1096 ◽  
Author(s):  
R. D. Stanley ◽  
D. L. Lee ◽  
D. J. Whitaker
Keyword(s):  
British Columbia ◽  
North America ◽  
Pacific Coast ◽  
Parasite Species ◽  
Stock Identification ◽  
Latitudinal Cline ◽  
Short Term ◽  
The Pacific ◽  
Stock Assessments ◽  
Biological Tags

We assessed the value of parasites of yellowtail rockfish, Sebastes flavidus (Pisces: Teleostei), as biological tags on the Pacific coast of North America. Of the 25 parasite species found, only Microcotyle sebastis (Monogenea: Microcotylidae) showed a latitudinal cline. Prevalence of this flatworm increased from 0–10% in samples from central British Columbia, to 80 and 100% in the California and Oregon samples, respectively. Mean intensity also increased from north to south. The results indicate that stock assessments for yellowtail rockfish, which treat the coastal population as five stocks from central British Columbia to northern California, can assume that harvests in one area will have little short-term impact on distant areas.

Two species of Grania (Oligochaeta, Enchytraeidae) from the Pacific Coast of North America

1980 ◽  
Vol 58 (6) ◽  
pp. 1037-1041 ◽  
Author(s):  
Kathryn Coates ◽  
Christer Erséus
Keyword(s):  
British Columbia ◽  
North America ◽  
Pacific Coast ◽  
The Pacific ◽  
Body Appearance

Grania paucispina (Eisen, 1904) and Grania incerta sp.nov. are described, both found in marine sands of California and British Columbia. The species are closely related. Their setae are morphologically very similar, and they both have small glands at their spermathecal openings which distinguish them from other species of the genus. They differ from each other primarily in the distribution of the setae and in body appearance.

Acanthochondria hippoglossi sp.nov. (Copepoda, Chondracanthidae), a crustacean parasite of some flatfishes off the Pacific coast of North America

1987 ◽  
Vol 65 (1) ◽  
pp. 213-216
Author(s):  
Z. Kabata
Keyword(s):  
British Columbia ◽  
North America ◽  
Pacific Coast ◽  
The Pacific ◽  
Hippoglossus Stenolepis ◽  
Hippoglossoides Elassodon

The female of Acanthochondria hippoglossi sp.nov. is described from the flatfishes Hippoglossus stenolepis and Hippoglossoides elassodon, taken off the shores of British Columbia. The confusion existing in the literature between this species and Acanthochondria cornuta is discussed and the presence of the latter species in the Pacific discounted.

scholarly journals The first record of a trionychid turtle (Testudines: Trionychidae) from the Cretaceous of the Pacific Coast of North America

2018 ◽  
Vol 5 ◽  
Author(s):  
Matthew J. Vavrek ◽  
Donald B. Brinkman
Keyword(s):  
British Columbia ◽  
North America ◽  
Late Cretaceous ◽  
Rocky Mountains ◽  
Pacific Coast ◽  
First Record ◽  
Vancouver Island ◽  
The Pacific ◽  
Western Interior Basin ◽  
Cretaceous Deposits

Trionychid turtles were widespread throughout much of the Western Interior Basin of North America during the Cretaceous, represented by a wide variety of taxa. Despite their widespread abundance east of the Rocky Mountains, they have not previously been reported from Cretaceous deposits along the Pacific Coast of North America. We report here on an isolated trionychid costal from Vancouver Island, British Columbia. The fossil was recovered from the Late Cretaceous (Turonian to Maastrichtian) Nanaimo Group, on Vancouver Island, British Columbia. While the fossil is generically indeterminate, its presence adds an important datapoint in the biogeographic distribution of Trionychidae.  

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

2014 ◽  
Vol 97 ◽  
pp. 170-192 ◽  
Author(s):  
Dan H. Shugar ◽  
Ian J. Walker ◽  
Olav B. Lian ◽  
Jordan B.R. Eamer ◽  
Christina Neudorf ◽  
...  
Keyword(s):  
North America ◽  
Sea Level ◽  
Pacific Coast ◽  
Sea Level Change ◽  
Level Change ◽  
The Pacific
Sign in / Sign up

Export Citation Format

Share Document