New Madrid Seismic Zone

The New Madrid Seismic Zone (NMSZ) has been responsible for producing some of the largest intraplate earthquakes on record (Tuttle et al., 2002). Paleoseismologic studies of sand blows and the Reelfoot fault show that earthquakes occurred in the last 4000 years at intervals of approximately 400-600 years (Kelson et al., 1995; Tuttle et al., 2002; Holbrook et al., 2006). The 1811-1812 NMSZ sequence produced three major earthquakes (M 7-8) followed by several large aftershocks and hundreds of smaller ones, resulting in a felt area that reached the east coast of the United States and caused destruction of several settlements along the Mississippi River due to liquefaction and strong shaking (Nuttli 1973, Johnston and Schweig, 1996). The risk of another large destructive earthquake in this region is of great concern to the USGS and local and federal authorities because several large metropolitan areas (Memphis, Little Rock, Nashville, St. Louis), and hundreds of smaller communities lie in or near the NMSZ. The mechanism for occurrence of earthquakes in the NMSZ is widely debated. Studies reveal the NMSZ is underlain by a failed rifting event, dating from late Precambrian. During the failed rifting event, emplacement of mafic plutons throughout the crustal column took place. Further studies show a correlation between the rift and current seismic activity. This correlation suggests that the source of the earthquakes was from slippage along weak zones within the failed rift caused by the E-W compressive stress of the region, a result of plate motion. Seismic monitoring shows that there is a spatial correlation of the active seismic zone with the failed Reelfoot Rift.