The New Madrid Earthquakes of 1811 and 1812 were three severe quakes over a 4 month period that affected the entire Mississippi/Ohio Valley. Among the ancedotes recorded in this earthquake were that: Church bells were rung (by the quake) in Boston, Sidewalks cracked in Washington DC. along with the facts that the Mississippi River ran backwards and so forth. In fact, the area was so altered that maps based on the old configuration of the river were rendered obsolete. (However, the state borders were defined by the old maps which is why you have areas that are cut off from the continguous states like the Kentucky Bend areaand Reverie, Tennessee, which lies on the Arkansas side of the Mississippi). Reelfoot Lake was a bend in the river cut off by the quake as the rivers course was changed.
Because of the configuration of the bedrock in the midwest, a quake can affect a vast area in comparison to a similar California quake. A 6.0 quake in California may affect a few counties, but a similar quake in the Midwest can be felt (and affect and DAMAGE) over several states as this one has. It woul be like a California quake affecting Las Vegas, Phoenix and Salt Lake City.
If an earthquake of the maginitude of the 1811 quake occoured the results would be disastorous. Memphis would be the new Katrina zone along with St. Louis. If it occoured in winter, areas of the Northeast would freeze and shut down as a majority of the Petrolium pipelines go through the zone. The majority of homes in St. Louis, along with its sewer system are of brick construction. Houses and streets would collapse rendering large parts of the city inaccessable and uninhabitable.
Needless to say, it would be a disaster of epic proportions. In 1990, eccentric scientist Iben Browing predicted that the New Madrid would generate an earthquake of epic proportions on December 2nd or 3rd of 1990 due to an allignment of the planets, sun and moon. Public officials took the predictions seriously enough that preparations were made for a disaster. The City of St. Louis parked some fire trucks in an open field in order that they not be crushed by the brick firehouses. I remember one television station putting out a special program on earthquake prepardness. Media gathered in New Madrid. Nothing happened. However, spurned on by the increase in awareness, state officials began quietly to upgrade local bridges and increase building codes to bring them in line with earthquake rediness. Local universities were granted some research dollars to increase study of the New Madrid Seismic Zone which covers areas of seven states.
The area doesn't have the research grants that the California area does in the field of Earthquake research because the quakes in the Midwest are rarely over 3.0. The recent quake has generated a 4.6 aftershock, but the vast majority have been in 2.0 to 3.0 range. Hopefully this isn't a precursor shock for an even bigger quake.