High-Resolution Seismic Imaging Investigations of Earthquake Hazards in the United States

PROJECT NARRATIVE The USGS-GHSC and University of Kentucky Cooperative Research Agreement G17AC00141 will consist of one (1) project site for FY2020-21: Wabash Valley seismic zone. The objectives for Year 4 (of 5) collaborative research continues our focus on using seismic-reflection imaging to characterize potential Quaternary-active faults. The Late-Precambrian–Early-Cambrian Wabash Valley fault system (WVFS) in the central United States is again the research target. This area of intraplate neotectonicism has a historic and contemporary record of small to moderate-sized earthquakes, called the Wabash Valley seismic zone. Moreover, the prehistoric record exhibits paleoliquefaction evidence for larger earthquakes with magnitude estimates ranging between M6.2 and M7.3. The WVFS is a narrow band of en echelon faults striking northeast from their southern truncation near the northern boundary of the east–west-oriented Rough Creek graben. The WVFS, including the primary Wabash Island, Hovey Lake, and Caborn fault strands, form narrow graben structures beneath the lower Wabash River valley of southern Indiana and Illinois, and western Kentucky. Prehistoric, historic, and instrumental seismic evidence have shown that small to moderate size earthquakes occur in an area located roughly coincident with the WVFS; however, the relatively low rate of seismicity and sparse long-term conventional seismic network coverage has generally made correlating earthquakes with specific geologic structure problematic. This year’s work includes a proposed 5-10 km of high- resolution SH-wave seismic reflection imaging across the targeted primary faults. The SH-mode technique will provide a higher imaging resolution relative to the conventional P-wave energy source; thus resulting in a better spatial and temporal understanding of the complex structural characteristics in the context of central United States earthquake hazards.