Stability of the Fraser River delta front

The distributary front deposits of the delta consist mainly of interlayered sand and silt and lie in one of the most seismically active zones in Canada. Subsurface deposits at the north tend to be siltier than those at the south. Sediments on the surface of the delta slope range from clayey silts at the north to pure sands at the south. Slope angles vary from 23° at the head of the slope to 1–2° within 2 km beyond the tidal flats.Hydraulic bedforms observed on the sandy slopes southeast of the main channel gradually increase in size from small ripples to large asymmetric sand waves 2–3 m high and approximately 30 m long. They are generated primarily by flood tidal currents which scour the seabed to a water depth in excess of 100 m.Formation of gullies which crease the delta slope probably is initiated principally by failure of oversteepened deposits at a channel mouth. Previous studies have suggested that the large hummocks or ridges at the base of the slope off the Main Channel have been formed by the compressional folding of failed deposits. Recent reflection seismic surveys suggest that such a process has recurred in this area during the growth of the delta.Interpretation of SPT data, in the light of recent research findings, suggests that previous analyses have overestimated failure potential. It is estimated that the slope may withstand an earthquake with a duration corresponding to approximately 15 significant cycles of motion and a peak acceleration in the range of 11–13% G. Keywords: stability, Fraser River Delta front, mass wasting, erosion, liquefaction potential, cyclic mobility.

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Tide-supported gravity flows on the upper delta front, Fraser River delta, Canada

Marine Geology ◽

10.1016/j.margeo.2012.09.007 ◽

2012 ◽

Vol 326-328 ◽

pp. 166-170 ◽

Cited By ~ 22

Author(s):

Korhan Ayranci ◽

D. Gwyn Lintern ◽

Philip R. Hill ◽

Shahin E. Dashtgard

Keyword(s):

River Delta ◽

Fraser River ◽

Delta Front ◽

Gravity Flows ◽

Fraser River Delta

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Infaunal holothurian distributions and their traces in the Fraser River delta front and prodelta, British Columbia, Canada

Palaeogeography Palaeoclimatology Palaeoecology ◽

10.1016/j.palaeo.2013.09.021 ◽

2013 ◽

Vol 392 ◽

pp. 232-246 ◽

Cited By ~ 12

Author(s):

Korhan Ayranci ◽

Shahin E. Dashtgard

Keyword(s):

British Columbia ◽

River Delta ◽

Fraser River ◽

Delta Front ◽

Fraser River Delta

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First Documented Large Failure At the Fraser River Delta Front, British Columbia

10.4095/122562 ◽

1987 ◽

Cited By ~ 1

Author(s):

G T McKenna ◽

J L Luternauer

Keyword(s):

British Columbia ◽

River Delta ◽

Fraser River ◽

Delta Front ◽

Fraser River Delta

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Large-scale mass-wasting events on the Fraser River delta front near Sand Heads, British Columbia

Canadian Geotechnical Journal ◽

10.1139/t92-016 ◽

1992 ◽

Vol 29 (1) ◽

pp. 151-156 ◽

Cited By ~ 33

Author(s):

G. T. McKenna ◽

J. L. Luternauer ◽

R. A. Kostaschuk

Keyword(s):

Large Scale ◽

River Mouth ◽

River Delta ◽

Silty Sand ◽

Fraser River ◽

Mass Wasting ◽

Coastal Structures ◽

Delta Front ◽

Liquefaction Hazard ◽

Fraser River Delta

Although the Fraser River delta front supports coastal structures including ports, a lighthouse, jetties, submarine power cables, and sewage pipelines, the stability of the delta front is little understood. Five large-scale mass-wasting events at the mouth of the Main Channel near Sand Heads have been detected by comparing successive bathymetric surveys conducted by Public Works Canada between 1970 and 1986. These events can involve the downslope movement of more than 1 × 106 m3 of silty sand and the landward retrogression of the delta-front crest of up to 350 m or more. Morphologic and sedimentologic evidence suggests that these events are slope failures which result from the liquefaction of silty sand. Rapid deposition at the river mouth is likely a prerequisite for failure, although interstitial gas, tidal currents, waves, and earthquakes also may contribute to failure. These results have important implications for the foundation stability of the Sand Heads Lighthouse and future coastal structures in the area. Key words : bathymetry, mass wasting, liquefaction, hazard, Fraser River delta.

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Seismic site response in the greater Vancouver, British Columbia, area: spectral ratios from moderate earthquakes

Canadian Geotechnical Journal ◽

10.1139/t98-096 ◽

1999 ◽

Vol 36 (2) ◽

pp. 195-209 ◽

Cited By ~ 11

Author(s):

John F Cassidy ◽

Garry C Rogers

Keyword(s):

Site Response ◽

Strong Motion ◽

River Delta ◽

Data Sets ◽

Fraser River ◽

Spectral Ratios ◽

Data Set ◽

Seismic Site Response ◽

Fraser River Delta ◽

S Period

Three-component, digital recordings of two recent moderate earthquakes provide valuable new insight into the response to seismic shaking in the greater Vancouver area, particularly on the Fraser River delta. The 1996 M = 5.1 Duvall, Washington, earthquake (180 km southeast of Vancouver) triggered strong-motion seismographs at seven sites and the 1997 M = 4.3 Georgia Strait earthquake (37 km west of Vancouver) triggered instruments at 13 sites in the greater Vancouver area. The latter data set is especially important because it contains the first three-component recordings made on bedrock in greater Vancouver. Both data sets represent weak ground motion, with peak horizontal accelerations of 0.5-1.5% gravity (g) for the Duvall earthquake, and 0.2-2.4% g for the Georgia Strait earthquake. Using the method of spectral ratios, we estimate the site response for each of the strong-motion instrument soil sites. On the Fraser River delta amplification is observed over a relatively narrow frequency range of 1.5-4 Hz (0.25-0.67 s period), with peak amplification of 4-10 (relative to competent bedrock) for the thick soil delta centre sites, and about 7-11 for the delta edge sites. Relative to firm soil, the peak amplification ranges from 2 to 5 for the thick soil delta centre sites, and 2 to 6 for the delta edge sites. At higher frequencies, little or no amplification, and in many cases slight attenuation, is observed.Key words: seismic site response, Fraser delta, earthquakes.

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