T36 Recent to Long-Term Slip Histories of Active Faults and Folds in Cascadia

Sunday, 10 October 2021
1:30 PM - 5:30 PM
A107–A109

PRELIMINARY AND VIRTUAL ASSESSMENT OF THE NEOTECTONICS OF THE EASTERN YAKIMA FOLD BELT AND QUINCY BASIN SCABLANDS GEOMORPHIC FEATURES, WASHINGTON

Paper number: T36-13
Program: Technical Sessions
Time: 4:25 PM – 4:40 PM

Authors

Abstract

Field geology traditionally involved on-site exploration and measurements, but in recent years field trips have been orchestrated virtually to simulate in person field excursions. The advancement of geodetic tools has assisted in this transition to the electronic. Due to the pandemic, the original two day field camp exercise was modified to an online week-long project. We studied Scablands geomorphology (Quincy Basin) and active folds (Yakima Fold Belt) in eastern Washington. These active folds are developed in the Columbia River flood basalts and younger strata in the Cascadia back-arc. Our analysis was conducted using publicly available data and software via: 1) literature review; 2) surface image, geomorphic analysis, and fold mapping on DEMs, HillShade images using Google Earth and ArcGIS; 3) geodesy using ready-to-go GPS from the University of Nevada-Reno Geodesy Lab; 4) elastic strain accumulation analysis via velocity profiling and using SSPX; 5) Washington DNR portal seismicity and published (USGS) paleoseismology reports; 5) the morphology of depositional and erosional features related to the Scablands flood. Pre-flood features in the Quincy Basin include dipping and folded basalts; flood features include erosional cataracts, plunge pools, scour holes, basalt excavations, and wind scours; depositional features include ripples (giant and small), and thick slack water deposits; post-flood sand dunes were also mapped. Geomorphologic mapping (patterns of wind and water gaps; eastward decrease in stream density) shows that the eastern Yakima anticlines (Saddle Mountains and Frenchman Hills) propagated eastward. GPS velocity data from 16 stations from the UN-Reno Geodesy Lab were used. Velocity gradients were calculated using excel and SSPX. Across the eastern Yakima folds, latitudinally, Vnorth, Veast, and Vup gradients, respectively, slope at -0.726, 0.582, and 0.1751. Longitudinally, Vnorth, Veast, and Vup gradients, respectively, slope at -0.6104, -0.3387, and 0.3171. Negative values indicate shortening and sinking. These outcomes show detectable N-S shortening, and W-E extension perpendicular to the folds.

Geological Society of America Abstracts with Programs. Vol. 53, No. 6

doi: 10.1130/abs/2021AM-369216

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