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125 Years of Science for America - 1879 to 2004
U.S. Geological Survey
Open-File Report 03-455
Version 1.0

The Catfish Lake Scarp, Allyn, Washington: Preliminary Field Data and Implications for Earthquake Hazards Posed by the Tacoma Fault

By Brian L. Sherrod, Alan R. Nelson, Harvey M. Kelsey, Thomas M. Brocher, Richard J. Blakely, Craig S. Weaver, Nancy K. Rountree, B. Susan Rhea, and Bernard S. Jackson


The Tacoma fault bounds gravity and aeromagnetic anomalies for 50 km across central Puget lowland from Tacoma to western Kitsap County. Tomography implies at least 6 km of post-Eocene uplift to the north of the fault relative to basinal sedimentary rocks to the south.

Coastlines north of the Tacoma fault rose about 1100 years ago during a large earthquake. Abrupt uplift up to several meters caused tidal flats at Lynch Cove, North Bay, and Burley Lagoon to turn into forested wetlands and freshwater marshes. South of the fault at Wollochet Bay, Douglas-fir forests sank into the intertidal zone and changed into saltmarsh. Liquefaction features found beneath the marsh at Burley Lagoon point to strong ground shaking at the time of uplift.

Recent lidar maps of the area southwest of Allyn, Washington revealed a 4 km long scarp, or two closely spaced en-echelon scarps, which correspond closely to the Tacoma fault gravity and aeromagnetic anomalies. The scarp, named the Catfish Lake scarp, is north-side-up, trends east-west, and clearly displace striae left by a Vashon-age glacier. A trench across the scarp exposed evidence for postglacial folding and reverse slip. No organic material for radiocarbon dating was recovered from the trench. However, relationships in the trench suggest that the folding and faulting is postglacial in age.

This report consists of a pamphlet and six figures printed on a single 36" x 36" sheet. Each figure is reduced in size or simplified for inclusion in this pamphlet. Readers are encouraged to print the larger figures on the 36"x36" sheet for greater detail and clarity.

Download the Pamphlet portion of this report as a PDF document (584 KB)

Download the figures sheet portion of this report as a 36-inch-square PDF document (16.1 MB).

For questions about the content of this report, contact Brian Sherrod

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Maintained by: Michael Diggles
Date created: June 7
Date last modified: June 7, 2004 (mfd)