Field and laboratory data from an earthquake history study of the Toe Jam Hill Fault, Bainbridge Island, Washington

Evidence for Late Holocene Earthquakes on the Utsalady Point Fault, Northern Puget Lowland, Washington

“…After modeling the recovery of the upper plate with elastic dislocation models, "residual" motions in the Puget Lowland and south Georgia Strait predict about 5 to 7 mm/yr of north-south shortening, which is assumed to be distributed on faults and folds. Thrust and reverse faulting on east-trending structures in the Puget Lowland, such as the Seattle and Tacoma faults (Johnson et al, 1994(Johnson et al, , 1999Blakely et al, 2002;Nelson et al, 2002Nelson et al, , 2003Sherrod et al, 2004), are consistent with this modeling, whereas left-lateral slip on east-southeast trending structures such as the Utsalady Point fault is not predicted.…”

“…Several postglacial fault scarps have recently been identified in the Puget Lowland using Airborne Laser Swath Mapping (ALSM) surveys (i.e., LIDAR), which can image low-relief landforms beneath forest canopies (Harding and Berghoff, 2000;Haugerud et al, 2003). Trenching investigations of ALSM-imaged backthrusts to the Seattle fault have documented three to four large, ground-rupturing earthquakes in the past ϳ2500 years (Nelson et al, 2002. This report describes a trench investigation of an ALSM-recognized scarp along the Utsalady Point fault in the northern Puget Lowland.…”

The Catfish Lake Scarp, Allyn, Washington: Preliminary field data and implications for earthquake hazards posed by the Tacoma fault

“…Uplifted terraces along the south side of the Seattle fault and a submerged intertidal marsh constrain a large earthquake on the Seattle fault zone to about 900-930 A.D. (Atwater and Moore, 1992;Bucknam et al, 1992). Surface rupture on a series of small en-echelon faults located within the Seattle fault zone suggest as many as three earthquakes in the last 2500 years (Nelson et al, 2002). Trenches across a scarp near Price Lake along the west side of Hood Canal yielded evidence for possibly three Holocene earthquakes (Wilson et al, 1979).…”

“…Maps produced from lidar surveys can show 'bare-Earth' topography by parsing the data to remove the effects of vegetation on topographic models. Detailed lidar maps show fault scarps within the Seattle fault zone at Toe Jam Hill on Bainbridge Island and Waterman Point near Port Orchard (Nelson et al, 2002). A newly discovered scarp between Catfish Lake and Prickett Lake near Allyn, Washington reveals the first evidence for surface rupture along the Tacoma fault (herein called the Catfish Lake scarp; Fig.…”

“…These faults include the Seattle, Tacoma, Olympia, and southern Whidbey Island, and bound structural basins beneath the cities of Tacoma, Seattle, and Everett (Brocher et al, 2001). Several faults are suspected of Quaternary offset, and the Seattle fault has Holocene rupture (Bucknam et al, 1992;Nelson et al, 2002).…”