"...are earthquakes really much of a threat in St. Louis?"

It does sound kind of strange, but YES. The New Madrid, MO area was the epicenter of the worst earthquake (actually a series of four major quakes) to have taken place in the continental U.S. between December 11, 1811 and February 7, 1812. The last quake was estimated to have hit 8.0 on the Richter Scale.

From Wikipedia: "There are estimates that the earthquakes were felt strongly over 50,000 square miles, and moderately across nearly one million square miles. The historic San Francisco earthquake of 1906, by comparison, was felt moderately over 60,000 square miles.

"As a result of the quakes, large areas sank into the earth, new lakes were formed (notably Reelfoot Lake, Tennessee), and the Mississippi River changed its course, creating Kentucky Bend. Nearby sections of the Mississippi River actually ran backwards for a short time. Sandblows were common throughout the area, and their effects can still be seen from the air in cultivated fields. Church bells were reported to ring in Boston, Massachusetts.

"The epicenters of over 4,000 earthquakes can be identified from seismic measurements taken since 1974. It can be seen that the earthquakes originate from the seismic activity of the Reelfoot Rift. The zone which is strongly colored in red on the map is called the New Madrid Seismic Zone.

"The zone remains active today. In recent decades minor earthquakes have continued. Scientists estimate that in the next 50 years, with a probability over 90%, there will be an earthquake with a magnitude greater than 7 on the Richter scale.

"The situation is more precarious than it was 200 years ago. The area is now more densely populated, and many buildings have no earthquake resistant construction. A few states have joined forces and founded a special institute for their earthquake zone, to prepare as well as possible for a major earthquake. The Mississippi River will probably present one of the incalculable problems."

Sue