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WITHDRAWN A Multi-scale Look Utilizing Seismic Reflection Profiles and Paleoseismic Trenching Across Quaternary Active Faults in the Kittitas Valley, Washington, USA

Description: 

WITHDRAWN The Kittitas Valley, located in central Washington State, USA, is a low-relief basin within the northwest corner of the Yakima fold province, a region of active NNE-SSW shortening in the backarc of the Cascadia subduction zone. Our study focuses on the Dead Coyote and Craigs Hill faults, two en echelon faults that transect the valley and parallel the prominent and active fault-cored anticlinal ridges to the south. To understand the subsurface geometries, relative timing, and rate of deformation of these individual structures in the Kittitas Valley, we combine observations from multi-scale seismic reflection datasets, including legacy industry profiles (~4.5 km depth) and ~7.5 km of new high-resolution profiles (<1.5 km depth), with tectonic geomorphic mapping and paleoseismic trenching. The seismic data reveal shallow north-vergent anticlinal folding beneath an east-west trending set of fluvially incised knolls that define the queried Craigs Hill fault trace in the middle of the valley. Conversely, south-vergent folding is observed below the Dead Coyote fault scarp, located ~6 km to the north. Stratigraphic and structural relationships of late Pleistocene glacial drift deposits and Quaternary colluvial deposits within two trench exposures across the Dead Coyote fault scarp indicate multiple episodes of late Quaternary surface faulting above a south-verging thrust fault. Optically stimulated luminescence dating results, supported by pedogenic characteristics of buried soils developed on scarp-derived colluvial wedges, indicate long recurrence intervals of rupture with the most recent earthquake occurring at <5.3 ka and the penultimate earthquake occurring at <60.3 ka. Our findings suggest that these seismogenic faults within the populated Kittitas Valley accommodate and transfer transpressional regional strain westward across the Cascade Mountains.

Session: The Landscape Record of Earthquakes and Faulting [Poster]

Type: Poster

Date: 4/16/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Stephen

Student Presenter: No

Invited Presentation: 

Poster Number: 2

Authors