Influence of the megathrust earthquake cycle on upper-plate deformation in the Cascadia forearc of Washington State, USA

Authors

Jaime E. Delano, Western Washington University
Colin B. Amos, Western Washington University
John P. Loveless, Smith CollegeFollow
Tammy M. Rittenour, Utah State University
Brian L. Sherrod, University of Washington
Emerson M. Lynch, Smith College

Document Type

Article

Publication Date

11-1-2017

Publication Title

Geology

Abstract

The influence of subduction zone earthquake cycle processes on permanent forearc deformation is poorly understood. In the Cascadia subduction zone forearc of Washington State, USA, deformed and incised fluvial terraces serve as archives of longer-term (103–104 yr) strain manifest as both fluvial incision and slip on upper-plate faults. We focus on comparing these geomorphic records in the Wynoochee River valley in the southern Olympic Mountains with short-term (101 yr) deformation driven by interseismic subduction zone coupling. We use optically stimulated luminescence dating and high-resolution elevation data to characterize strath terrace incision and differential uplift across the Canyon River fault, which cuts Wynoochee River terraces. This analysis demonstrates reverse slip rates of ∼0.1–0.3 mm/yr over the past ∼12–37 k.y., which agree with rates predicted by a GPS-constrained boundary element model of interseismic stress from Cascadia subduction zone coupling. Similarly, model-predicted patterns of interseismic uplift mimic the overall pattern of incision in the lower Wynoochee River valley, as revealed by strath elevations dated at 14.1 ± 1.2 ka. Agreement between modeled short-term and observed long-term records of forearc strain suggests that interseismic stress drives slip on upper-plate faults and fluvial incision in Cascadia. Consistency over multiple time scales may indicate relative stability in spatial patterns of subduction zone coupling over at least ∼104 yr intervals.

Volume

45

Issue

11

First Page

1051

Last Page

1054

DOI

doi.org/10.1130/G39070.1

Rights

Licensed to Smith College and distributed CC-BY under the Smith College Faculty Open Access Policy.

Comments

Peer reviewed accepted manuscript.

Recommended Citation

Delano, Jaime E.; Amos, Colin B.; Loveless, John P.; Rittenour, Tammy M.; Sherrod, Brian L.; and Lynch, Emerson M., "Influence of the megathrust earthquake cycle on upper-plate deformation in the Cascadia forearc of Washington State, USA" (2017). Geosciences: Faculty Publications, Smith College, Northampton, MA.
https://scholarworks.smith.edu/geo_facpubs/24