Log of an exploratory trench in the New Madrid seismic zone near Blytheville, Arkansas

During the winter of 1811-12, at least three major earthquakes having estimated magnitudes of M_S 8.3-8.8 (Nuttli and Herrmann, 1984) struck the area near New Madrid, Mo. Since the 1811-12 series of earthquakes, 20 damaging earthquakes have occurred in the area (Nuttli, 1982), making the New Madrid seismic zone (fig. 1) the most seismically active area in the Eastern United States (Hadley and Devine, 1974).  The zone, extending from about lat 35° to 37° N., approximately parallels the Mississippi River and encompasses an area roughly 50 km wide (Nuttli, 1979).