Skip to main content
U.S. flag

An official website of the United States government

Subsurface geometry and evolution of the Seattle fault zone and the Seattle Basin, Washington

January 1, 2002

The Seattle fault, a large, seismically active, east-west-striking fault zone under Seattle, is the best-studied fault within the tectonically active Puget Lowland in western Washington, yet its subsurface geometry and evolution are not well constrained. We combine several analysis and modeling approaches to study the fault geometry and evolution, including depth-converted, deep-seismic-reflection images, P-wave-velocity field, gravity data, elastic modeling of shoreline uplift from a late Holocene earthquake, and kinematic fault restoration. We propose that the Seattle thrust or reverse fault is accompanied by a shallow, antithetic reverse fault that emerges south of the main fault. The wedge enclosed by the two faults is subject to an enhanced uplift, as indicated by the boxcar shape of the shoreline uplift from the last major earthquake on the fault zone. The Seattle Basin is interpreted as a flexural basin at the footwall of the Seattle fault zone. Basin stratigraphy and the regional tectonic history lead us to suggest that the Seattle fault zone initiated as a reverse fault during the middle Miocene, concurrently with changes in the regional stress field, to absorb some of the north-south shortening of the Cascadia forearc. Kingston Arch, 30 km north of the Seattle fault zone, is interpreted as a more recent disruption arising within the basin, probably due to the development of a blind reverse fault.

Publication Year 2002
Title Subsurface geometry and evolution of the Seattle fault zone and the Seattle Basin, Washington
DOI 10.1785/0120010229
Authors Uri S. ten Brink, P.C. Molzer, M. A. Fisher, R. J. Blakely, R.C. Bucknam, T. Parsons, R. S. Crosson, K. C. Creager
Publication Type Article
Publication Subtype Journal Article
Series Title Bulletin of the Seismological Society of America
Index ID 70024616
Record Source USGS Publications Warehouse
USGS Organization Woods Hole Coastal and Marine Science Center