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Scientific Investigations Map 2961

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## Field and Laboratory Data From an Earthquake History Study of Scarps of the Lake Creek–Boundary Creek Fault Between the Elwha River and Siebert Creek, Clallam County, Washington

#### By Alan R. Nelson,1 Stephen F. Personius,1 Jason Buck,2 Lee-Ann Bradley,1 Ray E. Wells,3 and Elizabeth R. Schermer4

| *SIM 2961 Sheet 1*Large File Warning!                PDF (46.4 MB)                Right-Click to 'Download' or 'Save As'*SIM 2961 Sheet 1*Large File Warning!              PDF (46.4 MB)              Right-Click to 'Download' or 'Save As'
Fault scarps recently discovered on Airborne Laser Swath Mapping (ALSM; also known as LiDAR) imagery show Holocene movement on the Lake Creek–Boundary Creek fault on the north flank of the Olympic Mountains of northwestern Washington State. Such recent movement suggests the fault is a potential source of large earthquakes. As part of the effort to assess seismic hazard in the Puget Sound region, we map scarps on ALSM imagery and show primary field and laboratory data from backhoe trenches across scarps that are being used to develop a latest Pleistocene and Holocene history of large earthquakes on the fault. Although some scarp segments 0.5–2 km long along the fault are remarkably straight and distinct on shaded ASLM imagery, most scarps displace the ground surface <1 m, and, therefore, are difficult to locate in dense brush and forest. We are confident of a surface-faulting or folding origin and a latest Pleistocene to Holocene age only for scarps between Lake Aldwell and the easternmost fork of Siebert Creek, a distance of 22 km. Stratigraphy in five trenches at four sites help determine the history of surface-deforming earthquakes since glacier recession and alluvial deposition 11–17 ka. Although the trend and plunge of indicators of fault slip were measured only in the weathered basalt exposed in one trench, upward-splaying fault patterns and inconsistent displacement of successive beds along faults in three of the five trenches suggest significant lateral as well as vertical slip during the surface-faulting or folding earthquakes that produced the scarps. Radiocarbon ages on fragments of wood charcoal from two wedges of scarp-derived colluvium in a graben-fault trench suggest two surface-faulting earthquakes between 2,000 and 700 years ago. The three youngest of nine radiocarbon ages on charcoal fragments from probable scarp-derived colluvum in a fold-scarp trench 1.2 km to the west suggest a possible earlier surface-faulting earthquake less than 5,000 years ago.       | Version 1.0

Posted March 2007
-  **Sheet 1** PDF (46.4 MB)  This text-only version of Sheet 1 is accessible as defined in Section 508. 
-  **Sheet 2** PDF (11.6 MB) 

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1U.S. Geological Survey, Box 25046, Denver, CO 802252LACO Associates, 21 West 4th Street, Eureka, CA 955013U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 940254Western Washington University, Department of Geology, Bellingham, WA 98225 

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**Suggested citation:**

Nelson, A.R., Personius, S.F., Buck, Jason, Bradley, L.-A., Wells, R.E., and Schermer, E.R., 2007, Field and laboratory data from an earthquake history study of scarps of  the Lake Creek–Boundary Creek fault between the Elwha River and Siebert Creek, Clallam County, Washington:  U.S. Geological Survey Scientific Investigations Map 2961, 2 sheets.

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U.S. Department of the Interior | U.S. Geological Survey	URL: *http://pubsdata.usgs.gov/pubs/sim/2007/2961/index.html*	Questions or Assistance: Contact USGS	Last modified: Thursday, 01-Dec-2016 17:08:09 EST