Earthquakes In The Midwestern and Eastern United States?!

Most people think that earthquakes occur only in places like California, Alaska, and Japan. This couldn't be further from the truth. Several major and numerous minor earthquakes have occurred in the midwestern and eastern United States, as well as eastern Canada. Some of the earthquakes that have caused notable damage in these areas are listed below.

You probably noticed that in the list above, the magnitudes of earthquakes that took place in the 1800's are described as "estimated." This is because these earthquake events took place before the Richter magnitude scale was put in place. The approximation is made by a study of accounts of the earthquake which are correlated with the damage described in the Mercalli intensity scale, which, as you may recall, allows a classification of an earthquake's magnitude by ordinary people (not just seismologists). The descriptions may come even from personal correspondance of average citizens and include telling details about the damage the earthquake caused.

Over 900,000 earthquakes occur worldwide each year. Fortunately, the vast majority of them are magnitude 2.5 or less, and great earthquakes (magnitude 8.0 or more) only happen about once every 5 to 10 years. Most of these great quakes occur along the plate boundaries, not in the eastern and midwestern U.S.

A few areas of the midwestern and eastern United States are more prone to earthquakes than others. The most earthquake-prone areas include Charleston, South Carolina, eastern Massachusetts, the St. Lawrence River area, and the central Mississippi River Valley. Others sections of this part of the country are prone to earthquakes, but can expect fewer quakes of smaller magnitude. Below is a map showing the risk of damage by earthquakes for the continental United States.



Figure 1 (Modified from Stearns & Miller, 1977)

The central Mississippi River Valley and the Charleston, South Carolina, are more prone to damage during earthquakes than the northern part of the country. These areas have sandy soils that shake more than solid rock, resulting in damage from subsidence during an earthquake. The high water tables along the Mississippi and near the coast also increase the risk of soil liquefaction during strong earthquakes.


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