Abstract
The continental margin west of Oregon and Washington undergoes a northwardtransition in morphology, from a relatively narrow, steep slope west of Oregon to a broad,midslope terrace off Washington. Multichannel seismic (MCS) reflection data collected over theaccretionary complex show that the morphologic transition is accompanied by significant changein accretionary style: West of Oregon the direction of thrust vergence in the wedge toe flip-flopsbetween landward and seaward, whereas off Washington, thrust faults in the toe vergeconsistently landward, except near the mouth of the Columbia River where detachment folding ofaccreted sediment is evident. Furthermore, rocks under the broad midslope terrace west ofWashington appear to be intruded by diapirs. The combination of detachment folding, diapirs, andlandward- vergent thrust faults all suggest that nearly as far landward as the shelf break, couplingalong the interplate decollement is, or has been, low, as suggested by other lines of evidence. ©1998 Elsevier Science Ltd. All rights reserved.
Published Version
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