A P- and SH-wave seismic reflection investigation of the Kentucky Bend scarp in the New Madrid seismic zone

An on-going high-resolution seismic reflection investigation, integrating P- and SH-wave reflection techniques, is being conducted in the central New Madrid seismic zone to describe the geometry and style of the geologic structure associated with a NW-SE fault at the Kentucky Bend scarp (KBFS). To date, approximately 1.9 km of P-wave data and 0.9 km of SH-wave data have been collected. Two perpendicular six-fold P-wave reflection surveys have been performed obliquely to the axis of the KBFS to image the style and azimuth of structure associated with the deeper Cretaceous (427 m) and Paleozoic (533 m) reflection horizons. The P-wave data also served as reconnaissance for siting the target areas imaged by the near-surface SH-wave technique. A high-angle reverse fault has been successfully imaged 540 m in front (northeast) of the present scarp topography using P- and SH-wave techniques, indicating a broad zone of near-surface deformation. The fault, along with north-dipping reflectors, has been traced from the top of the Paleozoic bedrock into the water-saturated, unconsolidated sand and gravel of the Quaternary alluvium. It is interpreted to be a northeast-vergent fault, striking approximately N30°W. This interpretation is consistent with the surface expression of the scarp and the nature of the contemporary seismicity. The fault is also spatially consistent with historic reports of the two waterfalls created in the Mississippi River after the great 1811-1812 earthquakes, suggesting that the KBFS represents part of the surface rupture associated with the events.