INTRAPLATE SEISMICITY: ANNALS OF THE NEW MADRID SEISMIC ZONE, CENTRAL US (Invited Presentation)

The New Madrid seismic zone (NMSZ) is an intraplate right-lateral strike-slip and thrust fault system, mostly located in the Mississippi Alluvial Valley that is the latest reactivation of deep basement faults. The Quaternary paleoseismic record, developed using historic data, paleoliquefaction features, some associated with archeologic artifiacts, and surface deformation indicates that there have been five sequences, four prehistoric and one historic (1811-1812), of earthquakes during the past 2.6 ky within the seismic zone. In addition, there are clusters of Holocene and late Pleistocene seismic activity in nearby areas of the central US. Movement along the major Reelfoot thrust fault with a recent mean short-term slip rate of 1.3 cm/year during the last two seismic sequences and a late Holocene long-term slip rate of 0.4-0.6 cm/year through the last three seismic sequences, has resulted in surface folding and uplift to form the Tiptonville dome and adjacent Reelfoot Lake. Lateral motion marked by recorded seismicity but subtle vertical deformation in the form of “sunklands” and tilted stream terraces where the uplifts cross streams and aggradation where depressions transect streams, has also occurred along adjoining strike-slip Reelfoot fault segments. Lateral motion without recorded seismicity is marked by truncated landscape features and concentrations of sand blows along the Bootheel fault, possibly a linking fault between the northern and southern strike-slip segments of the Reelfoot fault. Proposed causes of the late Quaternary NMSZ reactivation are a right-lateral shear across the Reelfoot Rift in a weak lower crustal zone where some perturbation in the stress field, pore pressure and/or thermal state initiates instability. Possible perturbations that have been proposed include a favorable orientation to North American stress field, high heat flow from a buried rift pillow, glacial unloading after the Wisconsin ice melted, and erosion and isostatic rebound of the Mississippi.