Pacific Coastal & Marine Science Center
National Seafloor Mapping and Benthic Habitat Studies
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Duwamish Delta (680 kb) - Puyallup Delta (650 kb)
Nisqually Delta (400 kb) - Selected Views
A magnitude 6.8 earthquake struck southern Puget Sound on February 28, 2001 and caused an estimated $0.7 to $1.4 billion in damages to buildings and roadways in the region (Williams et al., 2001). The earthquake source was 52 km deep with the epicenter located close to the Nisqually River delta in the same location as the M7.1 earthquake of 1949. These deep earthquakes occurred in the subducting slab of the Juan de Fuca plate and typically caused less damage than shallow, crustal events of the same magnitude. Geologists inspected the region immediately after the recent earthquake and reported numerous ground failures, including landslides along coastal bluffs, lateral spreads, and liquefaction of alluvial sediment in low-lying valleys. Silt-laden water, or "mud plumes" were also observed offshore the major river deltas in southern and central Puget Sound, suggesting that submarine landslides may have occurred on the seaward-sloping delta fronts. For more information on the Nisqually earthquake, please visit the USGS, Earthquake Hazards Program.
A joint NOAA/USGS cruise was rapidly organized to examine the submerged parts of the Duwamish River delta (Seattle), Puyallup River delta (Tacoma), and Nisqually River delta (a wildlife refuge). During the period from March 19 to 30, 2001, the NOAA Ship Rainier used high-resolution multibeam systems to map the bathymetry of these areas. A variety of submarine failures were observed on the Puyallup and Duwamish deltas that may be related to the earthquake. Several known landslides, such as the 1894 landslide on the Puyallup delta and the 1986 Duwamish Head failure were also observed in the data, as well as previously undescribed failures.
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For more information and to download the multibeam bathymetry data in two formats, XYZ ASCII and ArcInfo GRID, please see U.S. Geological Survey Open-File Report OF01-266.
Williams, C.R., Windeler, D.S., Rahnama, M., Morrow, G.C., and Rodriguez, A., 2001, Insured loss estimates for the 28 February 2001 Nisqually earthquake. Seismological Soc. Amer. Ann. Mtg., San Francisco, CA.