Nisqually Earthquake, Washington February 28, 2001
The Geologic Hazards Team from Golden, CO
Post-Nisqually-Earthquake Investigations—Bucknam and Lidke
Based on reports of liquefaction in several areas near Seattle, Bucknam and David Lidke (Earth Surface Processes Team) spent the afternoon of March 1 searching for evidence of liquefaction in the valley of the Green River between Kent and Auburn, but no evidence was found.
The following day, we searched the Lynch Cove marsh area near Belfair and the Skokomish River delta area on Hood Canal for evidence of liquefaction or lateral spreading. Both of these areas in central and southwest Puget Sound region have thick accumulations of poorly consolidated sediment in river valleys and the heads of large bays that would be expected to have the potential toliquefy under high ground motion. Discussions with people who live and work at both areas indicated that no one had reported seeing any evidence of liquefaction, nor did we see any in our reconnaissance observations at either site.
Gerald Elfendahl of Bainbridge Island reported that he drove and searched on foot many parts of the island, including areas of artificial fill in Eagle Harbor, but found no evidence of ground failure.
We also examined two sites based on descriptions of ground failure by Christopher Dunagan, a reporter for the Bremerton Sun newspaper. One of these is a fractured interval of Highway 302 that borders the coast on the east side of North Bay (Case Inlet) near the town of Allyn (Photo 1). Gaping fissures with up to 40 cm vertical displacement in a 100-m-long zone have made the highway impasable. Chleborad and Schuster reported slumping of the highway in this area in the 1949 and 1965 earthquakes.
The second area of ground failure is at Lion's Park in East Bremerton (photo 2). Tennis courts at the crest of a 20-foot-high rounded hillslope at the park are fractured, and sand has been ejected from cracks on to the asphalt surface of the courts. The gaping fractures have vertical and horizontal displacements of about 5-10 cm. Fine sand ejected through some of the cracks contrasts with the fill material and indicates liquefaction of sediment below the fill. The cracks are roughly parallel to topographic contours and suggest settlement of fill used to level the ground for the courts. The fine sand ejected through some of the cracks contrasts with the fill material and indicates liquefaction of sediment below the fill.
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