![]() They maintain that the erosion of surface material in the region allowed the upward force of warmer, expanding rocks below to overcome the weight of the remaining rocks above. Some Earth scientists suggest that fracturing in this region resulted from stresses brought on by the downcutting of the Mississippi River into the surrounding landscape between 10,000 and 16,000 years ago. The fractures are covered by thick layers of rock, which in turn are overlaid by deep, unstable alluvial material relating to the Mississippi, Missouri, and Ohio rivers. Lying in the central area of the North American Plate, the seismic zone is about 45 miles (70 km) wide and about 125 miles (200 km) long. New Madrid Seismic Zone (NMSZ), region of poorly understood, deep-seated faults in Earth’s crust that zigzag southwest-northeast through Arkansas, Missouri, Tennessee, and Kentucky, U.S.
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