Multibeam mapping of the major deltas of southern Puget Sound, Washington

Abstract

A magnitude 6.8 earthquake struck southern Puget Sound, Washington, USA on February 28, 2001 causing an estimated $0.7 billion to $1.4 billion in damages to the surrounding area (Williams et al, 2001). The epicenter was close to the Nisqually delta, one of three major deltas in southern Puget Sound (Figure 1). The Nisqually delta is a wildlife refuge but the other two deltas, the Duwamish delta in Seattle and the Puyallup delta in Tacoma, support extensive infrastructure, including major port facilities at the delta edges. Teams of geologists inspected the area immediately after the earthquake and reported liquefaction features and areas of vertical ground displacement in the Ports of Seattle and Tacoma as well as the presence of "mud plumes" in the waters of Puget Sound. A joint NOAA/USGS cruise was rapidly assembled in March 2001 (3/19/01 to 3/30/01) to map the bathymetry of the delta fronts using the high-resolution multibeam systems of the NOAA Ship Rainier. The mapping discovered a variety of submarine failures on the Puyallup and Duwamish delta fronts that may be related to the earthquake.