Geometry and deformation history of the New Madrid seismic zone fault system, Central U.S. from high-resolution marine seismic reflection data, and implications for intraplate deformation

The New Madrid Seismic Zone (NMSZ) is the most seismically active area in the continental United States east of the Rocky Mountains, and by far the most studied intraplate seismic zone in the world. The occurrence of large magnitude historical and prehistorical earthquakes, as well as the high level of instrumental seismicity suggest that the North American plate is actively deforming in this region. This observation appears to clash with geodetic evidence that shows minimal motion across the faults illuminated by the present seismicity, suggesting that either the present GPS vectors recorded at the surface are not typical of the long term deformation rate of the NMSZ faults, or that the NMSZ fault system is presently unloaded and not deforming. To better constrain the long-term deformation history of the NMSZ fault system, in the summer of 2010 we acquired ~300 km of high-resolution seismic marine reflection data along the Mississippi River from Cape Girardeau, MO to Caruthersville, MO. The profile crosses a large portion of the Mississippi Embayment, including three of the four main NMSZ active faults, and images the gently south-dipping unconsolidated sediments of the Mississippi Embayment from the Quaternary alluvium of the Mississippi River down to the top of Paleozoic sequences, at a depth of ~650 m. Among the most remarkable structures imaged by the profile is the Reelfoot fault, interpreted as the NW-SE striking restraining bend connecting two NE-SW trending dextral strike-slip faults. The Reelfoot thrust intersects the profile at three locations along the river meander known as the Kentucky Bend. The multiple crossings allow mapping of the along-strike variations of the fault plane’s dip and structure. In particular the data show that a reverse offset of 42 m at the top of the Cretaceous is accommodated by a single fault at the crossing north of town of Tiptonville, TN, west of the location where the Reelfoot thrust ruptured during the 7 February 1812 M7.7 event. A few miles downriver (10 km), the data show that the Reelfoot thrust still consists of one single fault plane displacing the unconsolidated sediments and maintaining an offset of 38 m at the top of the Cretaceous sediments. Farther downriver to the northwest, where the Reelfoot thrust approaches the northern dextral strike-slip fault, the data show that the compression is accommodated by a series of small faults, suggesting that the Reelfoot fault splits into a system of splays. Where reflectors are well imaged, the data indicate that displacement along the Reelfoot fault increases with age of the sediments involved, implying a repeated reactivation of the fault through time.