Color shaded-relief bathymetry of the Duwamish delta in Elliott Bay, offshore Seattle, Washington. Contour interval 20 m. Onshore part of image is from a U.S. Geological Survey digital orthophotoquad (DOQ).
The delta front of the Duwamish River valley near Elliott Bay and Harbor Island is founded on young Holocene deposits shaped by sea-level rise, episodic volcanism, and seismicity. These river-mouth deposits are highly susceptible to seismic soil liquefaction and are potentially prone to submarine landsliding and disintegrative flow failure.
A highly developed commercial-industrial corridor, extending from the City of Kent to the Elliott Bay/Harbor Island marine terminal facilities, is founded on the young Holocene deposits of the Duwamish River valley. The deposits of this Holocene delta have been shaped not only by relative sea-level rise but also by episodic volcanism and seismicity. Ground-penetrating radar (GPR), cores, in situ testing, and outcrops are being used to examine the delta stratigraphy and to infer how these deposits will respond to future volcanic eruptions and earthquakes in the region. A geotechnical investigation of these river-mouth deposits indicates high initial liquefaction susceptibility during earthquakes, and possibly the potential for unlimited-strain disintegrative flow failure of the delta front.
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Suggested citation and version history
This is one of a series of chapters in Earthquake Hazards of the Pacific Northwest Coastal and Marine Regions, USGS Professional Paper 1661, edited by Robert Kayen. The others consist of:
Crustal Deformation at the Leading Edge of the Oregon Coast Range Block, Offshore Washington (Columbia River to Hoh River), USGS Professional Paper 1661-A, by Patricia A. McCrory, David S. Foster, William W. Danforth, and Michael R. Hamer
Crustal Structure of the Cascadia Fore Arc of Washington, USGS Professional Paper 1661-D, by Tom Parsons, Richard J. Blakely, Thomas M. Brocher, Nikolas I. Christensen, Michael A. Fisher, Ernst Flueh, Fiona Kilbride, James H. Luetgert, Kate Miller, Uri S. ten Brink, Anne M. Trehu, and Ray E. Wells
Turbidite Event History—Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone, USGS Professional Paper 1661-F, by Chris Goldfinger, C. Hans Nelson, Ann E. Morey, Joel E. Johnson, Jason R. Patton, Eugene Karabanov, Julia Gutiérrez-Pastor, Andrew T. Eriksson, Eulàlia Gràcia, Gita Dunhill, Randolph J. Enkin, Audrey Dallimore, and Tracy Vallier
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