In the United States, most earthquakes occur along the active plate boundaries in California, Oregon, Washington, and Alaska. If you live in one of these states, you may have felt an earthquake. However, several of the largest earthquakes ever recorded in the United States occurred in the Midwest, far from any plate boundary. These earthquakes took place in an area called the New Madrid Fault Zone, named after the town of New Madrid, Missouri. Over a three-month period in the winter of 1811 to 1812, the New Madrid Fault Zone was struck by three huge earthquakes estimated to be greater than magnitude 8.0. Aftershocks were felt in the region for more than a year. These included seven aftershocks between magnitude 7 and 8, ten between magnitude 6 and 7, and eighty_nine between magnitude 4 and 5. Many aftershocks were strong enough to ring church bells on the east coast of the United States.

Modified Mercalli Scale, based on maps in W. Atkinson, 1989, The Next New Madrid Earthquake, Southern Illinois, University Press.