PRELIMINARY VIRTUAL INVESTIGATION OF THE NEOTECTONICS OF THE YAKIMA FOLD BELT USING EMERGING DIGITAL MAPPING AND GEODETIC TECHNIQUES

The Yakima Fold Belt is a tectonically active, wedge-shaped region in southeastern Washington that lies in the back-arc basin east of the Cascade Range and west of the North American craton. Miocene-aged Columbia River flood basalts and younger overlying sedimentary strata are being actively folded due to deformation at the junction of the Oregon block, the Walker Lane, and the northern Basin and Range. This produces trains of ~E-W oriented asymmetrical anticlines and synclines of 50-100km in length; anticlines are cored by blind thrust faults. We examined this region for one week during the UH 2021 summer field camp; three publicly available data sets and associated techniques were used to study the ongoing regional deformation: 1) Hillshade images were created in ArcGIS using DEM data from the Washington Department of Resources. These hillshade images were used to map the folds and associated faults, as well as map key geomorphic features such as elevation gradients, drainage patterns, and wind gaps. 2) USGS NEIC earthquake epicenters from 1969 to 2019 were plotted. Recurrence intervals of >2.5, >3.0, and >4.0 magnitude earthquakes were found to be: 0.1825, 0.6410, and 8.333 years, respectively and a fault scaling profile showed that all anticlines in the region have the potential to create earthquakes of a 7.0 magnitude or greater. Additionally, several potential trench sites were identified for later logging of paleoseismic records to better assess long-term earthquake hazard levels. 3) GPS data from UN-Reno Geodesy Lab (precision levels are v_Horizontal ~±0.14-0.35 mm/yr & v_Up ~±0.42-1.12 mm/yr) was analyzed using rudimentary Microsoft Excel plots and SSPX to investigate velocity gradients. ~N-S shortening elastic strain accumulation is highest in the south (Horse Heaven Hills). Geomorphic analysis shows that these anticlines propagate to the east; elevation profiles along axial traces show elevation decreases to the east; we also noted characteristic “bent” and low-density drainage patterns around the noses of the anticlines; location of wind gaps are also consistent with eastward migration of tributaries to the major rivers (Columbia and Yakima) in the region. Active folding in the Yakima Fold Belt should motivate further study since fault scaling indicates the potential for large (M>7.0) earthquakes and geomorphology and geodesy indicate active fold growth.