USING THE HVSR METHOD TO MAP BEDROCK TOPOGRAPHY AND DRIFT THICKNESS OF THE PREGLACIAL TEAYS RIVER VALLEY IN THE ANNA SEISMIC ZONE, OHIO

To better characterize the near-subsurface geology in the preglacial Teays River Valley, the Ohio Department of Natural Resources, Division of Geological Survey mapped bedrock topography and drift thickness in the Botkins and New Knoxville 7.5-minute quadrangles in Ohio. Previous geologic mapping efforts in the area were inadequate to define the geomorphology of the valley. During the field season of 2017, H-to-V Spectral Ratio (HVSR) data were collected and compiled into ArcGIS® to produce a detailed bedrock-topography map, which shows a well-defined, more gorge-like buried valley than previously interpreted. The Village of Anna, Ohio, sits directly on top of the deepest section of the buried valley, where glacial drift reaches more than 600 feet thick. Such thick deposits amplify seismic waves, which may explain why Anna suffered moderate damage in comparison to nearby towns during the M4.9 and M5.4 earthquakes of 1937. Documenting thickness and shear wave velocity of the glacial drift in the Anna Seismic Zone will lead to increased understanding of the likelihood and behavior of seismic amplification from earthquakes throughout the region.