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

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

doi:10.3133/ofr03455

Cited by 2 publications

(1 citation statement)

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“…The lineaments are ∼80-m wide sloping surfaces that form scarplike linear features that we will refer to as fold scarps. A trench dug across one of these lineaments, the Catfish Lake fold scarp, showed a fold in the strata with more than 2 m of vertical relief, up to the north, but only minor faulting (< 30 cm; Sherrod et al, 2003Sherrod et al, , 2004. Their interpretation of the trench exposure is that the fold scarp is caused by warping of the postglacial surface above a blind fault tip.…”

Section: Previous Workmentioning

confidence: 99%

High-Resolution Seismic Reflection Imaging of Growth Folding and Shallow Faults beneath the Southern Puget Lowland, Washington State

Clement¹,

Pratt²,

Holmes³

et al. 2010

Bulletin of the Seismological Society of America

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Marine seismic reflection data from southern Puget Sound, Washington, were collected to investigate the nature of shallow structures associated with the Tacoma fault zone and the Olympia structure. Growth folding and probable Holocene surface deformation were imaged within the Tacoma fault zone beneath Case and Carr Inlets. Shallow faults near potential field anomalies associated with the Olympia structure were imaged beneath Budd and Eld Inlets. Beneath Case Inlet, the Tacoma fault zone includes an ∼350-m wide section of south-dipping strata forming the upper part of a fold (kink band) coincident with the southern edge of an uplifted shoreline terrace. An ∼2 m change in the depth of the water bottom, onlapping postglacial sediments, and increasing stratal dips with increasing depth are consistent with late Pleistocene to Holocene postglacial growth folding above a blind fault. Geologic data across a topographic lineament on nearby land indicate recent uplift of late Holocene age. Profiles acquired in Carr Inlet 10 km to the east of Case Inlet showed late Pleistocene or Holocene faulting at one location with ∼3 to 4 m of vertical displacement, south side up. North of this fault the data show several other disruptions and reflector terminations that could mark faults within the broad Tacoma fault zone. Seismic reflection profiles across part of the Olympia structure beneath southern Puget Sound show two apparent faults about 160 m apart having 1 to 2 m of displacement of subhorizontal bedding. Directly beneath one of these faults, a dipping reflector that may mark the base of a glacial channel shows the opposite sense of throw, suggesting strike-slip motion. Deeper seismic reflection profiles show disrupted strata beneath these faults but little apparent vertical offset, consistent with strike-slip faulting. These faults and folds indicate that the Tacoma fault and Olympia structure include active structures with probable postglacial motion.

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Section: Previous Workmentioning

confidence: 99%