Structure of the eastern Seattle fault zone, Washington state: New insights from seismic reflection data

Liberty, L. M.; Pratt, T. L.

Abstract:

We identify and characterize the active Seattle fault zone (SFZ) east of Lake Washington with newly acquired seismic reflection data. Our results focus on structures observed in the upper 1 km below the cities of Bellevue, Sammamish, Newcastle, and Fall City, Washington. The SFZ appears as a broad zone of faulting and folding at the southern boundary of the Seattle basin and north edge of the Seattle uplift. We interpret the Seattle fault as a thrust fault that accommodates north-south shortening by forming a fault-propagation fold with a forelimb breakthrough. The blind tip of the main fault forms a synclinal growth fold (deformation front) that extends at least 8 km east of Vasa Park (west side of Lake Sammamish) and defines the south edge of the Seattle basin. South of the deformation front is the forelimb break-through fault, which was exposed in a trench at Vasa Park. The Newcastle Hills anticline, a broad anticline forming the north part of the Seattle uplift east of Lake Washington, is interpreted to lie between the main blind strand of the Seattle fault and a backthrust. Our profiles, on the northern limb of this anticline, consistently image north-dipping strata. A structural model for the SFZ east of Lake Washington is consistent with about 8 km of slip on the upper part of the Seattle fault, but the amount of motion is only loosely constrained.

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Article

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70000290

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Liberty, L. M.; Pratt, T. L.

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1695

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English

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Bulletin of the Seismological Society of America

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Structure of the eastern Seattle fault zone, Washington state: New insights from seismic reflection data; 2008; Article; Journal; Bulletin of the Seismological Society of America; Liberty, L. M.; Pratt, T. L.