SHALLOW SEISMIC REFLECTION IMAGING OF THE IDALIA HILL FAULT ZONE, SOUTHEASTERN MISSOURI

Shallow seismic reflection imaging was used to characterize the significance of near-surface tectonic deformation associated with the northeast-trending Idalia Hill fault zone in southeastern Missouri. The fault zone is expressed by topographic escarpments, photolineaments, and subsurface faulting in Paleozoic through Quaternary deposits. Two shear-wave seismic reflection profiles (IDALIA 1 and IDALIA 2) were collected (in July, 2001) across the fault zone in order to identify the location and style of neotectonic deformation and help guide the placement of subsequent paleoseismic trenching activities. The processed seismic profiles show coherent seismic reflection energy to depths greater than 100 m. Based on correlation with local borehole data and previously acquired compressional-wave seismic reflection data, reflections from the Quaternary/Tertiary, Tertiary/Cretaceous and Cretaceous/Paleozoic boundaries have been identified on the S-wave reflection profiles. Changes in reflection amplitude and coherency suggest the presence of high-angle faults in the subsurface. Deformation features identified in a paleoseismic trench excavated in October, 2001, correlate with the updip projection of a fault interpreted on seismic line IDALIA 2. Future seismic investigations are planned in the area to image very shallow (<10 m deep) subsurface (Quaternary) deposits that do not show geomorphic expression of recent faulting.