APPLYING THE HVSR METHOD TO MAP BEDROCK TOPOGRAPHY AND THE DEEPLY BURIED TEAYS VALLEY IN CHAMPAIGN COUNTY, OHIO

Champaign County, Ohio, is almost entirely covered by unconsolidated sediment (glacial drift) and contains the thickest drift packages in the state—potentially reaching depths of approximately 245 m (804 ft) or more. Sparse control on the depth to bedrock in this region has presented challenges for various projects, such as subsurface modelling and natural resource characterization. The buried Teays River Valley occurs in this region and contains underutilized aquifers due to the uncertainty of its location. The Teays River once flowed northwestward through Ohio but was dammed during the pre-Illinoian Glaciation. Subsequent glaciations buried the main Teays Valley, leaving no evidence of this ancient river on the modern-day drift-covered landscapes in Champaign County, Ohio. Recent mapping efforts have dramatically improved the resolution of the buried bedrock surface through extensive geophysical surveying, revealing unique buried valley morphologies of the ancient Teays River System. The Horizontal-to-Vertical Spectral Ratio (HVSR) technique has been successfully employed in other parts of the state to remap the Teays Valley and has become a vital tool to help calculate unconsolidated material thickness estimates. HVSR data were obtained at over 1,600 unique sites in Champaign County throughout the two-year duration of the project. Approximately 160 HVSR points were used to develop eight separate calibration equations to spatially characterize average shear wave velocities at different depths and geologic materials. Data collected from passive seismic surveys, coupled with gravity and active seismic surveys, support a notably different Teays paleochannel location and morphology than previously interpreted. Data and interpreted results indicate that the buried Teays Valley in western Ohio exhibits varying meandering-to-linear drainage patterns and deep, gorge-like valley sides. These concealed geomorphological changes along different reaches of the trunk valley may be associated with Precambrian fault systems. Future bedrock topography refinement work will focus on the Teays Valley and other ancient tributaries in west-central Ohio to identify groundwater supplies, improve future infrastructure projects, and better develop this region’s glacial and preglacial history.