POSSIBLE SURFACE WARPING ALONG THE BOOTHEEL FAULT REVEALED FROM LIDAR, NEW MADRID SEISMIC ZONE, CENTRAL US

The north/northeast-striking Bootheel fault in the central U.S. is an active structural component of the New Madrid seismic zone fault complex, the source of M7 to 8 earthquakes in 1811-1812. The Bootheel fault was originally recognized from a tonal lineament visible on aerial photography, and coring across the lineament revealed >13 m right-lateral strike-slip Holocene offset with an up-on-the-southeast component of ~3 m. In this study, the treads of Late Pleistocene fluvial terraces of the Mississippi River, the 14-16 ka Kennett terrace and the 12 ka Morehouse terrace, were used as originally planar structural datums that cross the Bootheel fault. Using 10 m-resolution LiDAR, we constructed best-fit polynomial surfaces of these terraces to assess long-wavelength deformation of their treads. Our results reveal a subtle 4 m-deep, 40 km-wide, 180 km-long, topographic trough parallel to the Bootheel fault. The trough axis is an average of 5 to 10 km northwest of the fault and crosses obliquely from the Morehouse terrace to the Kennett terrace. The Malden-Bernie scarp separating the two terraces continues where it crosses the trough, but it is down-warped, inconsistent with an erosional origin of the trough. Typical topographic down-stepping from older to younger terrace treads is reversed across the southern segment of this trough such that the Morehouse tread is at a higher elevation than the Kennett tread. However, the Kennett tread was not buried by later deposition of Morehouse alluvium, suggesting the Morehouse terrace was uplifted to the southeast of the trough after terrace deposition. We interpret this trough as a subtle syncline in the northwestern block of the Bootheel fault that developed in response to up-on-the-southeast fault movement. If true, movement on the Bootheel fault has increased the syncline’s amplitude at an average rate of 0.3 mm/year over the last 12,000 years.