This week, over 50 small to moderate earthquakes have occurred near the town of Guy, Arksansas, only 50 miles north of Little Rock. The largest of these quakes registered 4.3, but most were less than 3.0 in magnitude. The New Madrid seismic zone that occupies a large span of the Mississippi River valley has been seismically active for over 4,500 years, producing massive quakes over 8.0. The last time this seismic system has produced an earthquake in this range was in 1811-1812 when three earthquakes registered 7.5-7.7.
Over the last 15 years, GPS studies seem to show that surface tension in this area has decreased, leading some to believe that stress beneath the surface is also decreasing. These latest tremors in the New Madrid fault zone is a clear indication that there may be another massive quake in the near future. The USGS estimates that the possibility of a series of shocks such as those in 1811-1812 within 50 years is 7-10%, and the possibility of a quake in the range of 6.0 or above in the next 50 years is 25-40%.
Over the past 200 years since the last massive shocks occurred in this area, cities such as Little Rock, Memphis, and St. Louis have exploded in size, but aging cities such as Memphis have many buildings not ready to withstand a tremor 6.0 in magnitude.