AN OVERVIEW OF TECTONIC EFFECTS ON THE MISSISSIPPI RIVER BY PRIMARY NEW MADRID FAULTS

Mississippi River deposits reveal a history of channel responses to gradient-altering deformation on both the traversing Reelfoot and Cottonwood Grove faults, lending insights into timing and location of past slip.

The meandering Mississippi River currently responds to uplift on the Reelfoot scarp by straightening its course where it traverses the lowered up-dip slope. This modern straightening initiated with the AD900 slip event, and was reinforced by later AD1450 and AD1812 events. The river also compensated for the latter two events by aggradation/incision and channel combing. Mapping indicates a comparable middle Holocene episode of straightening initiating around 2200BC which speaks of a similar episode of slip separated from the modern episode by at least 1700 years. This is suggestive of millennial-scale temporal clustering of large slip events on the Reelfoot fault.

Floodplain deposits are down-warped two meters over the Cottonwood Grove fault 2.5km northwest of Cottonwood Point, Missouri, at the likely epicenter of the 12/16/1811 dawn earthquake. Deformation resulted in Pemiscot Big Lake sunklands above the down-dropped northern fault block. Silt-dominated splay deposits from the proximal Mississippi River filled over 1.5 meters of the initial relief. Pemiscot Big Lake is historically reported to have formed during the 1811/1812 earthquake sequence; however, it is uncertain if all of the relief recorded accumulated in the 1811 event. The splay is underlain by a large breakout of the Mississippi River channel that sent an anastomosing network into the same area during middle Holocene, suggestive of much earlier deformation at this site.