by Duane Friend
When people think of earthquakes in the United States, they tend to think of the west coast. But earthquakes also happen in the eastern and central U.S. The following information comes from the United States Geological Survey.
Until 2014, when the dramatic increase in earthquake rates gave Oklahoma the number one ranking in the conterminous U.S., the most seismically active area east of the Rocky Mountains was in the Mississippi Valley area known as the New Madrid seismic zone. Since 1974, seismometers, instruments that measure ground shaking, have recorded thousands of small to moderate earthquakes. The faults that produce earthquakes are not easy to see at the surface in the New Madrid region because they are eroded by river processes and deeply buried by river sediment. This earthquake activity defines several branches of the New Madrid seismic zone in northeastern Arkansas, southwestern Kentucky, southeastern Missouri and northwestern Tennessee. Some faults extend into southern Illinois, as well.
Studies have concluded that the New Madrid seismic zone generated magnitude 7 to 8 earthquakes about every 500 years during the past 1,200 years. The most recent major activity occurred in 1811 and 1812, when three major quakes and hundreds of smaller ones occurred over several months.
What are our chances of getting a major or even a moderate earthquake in the next 50 years? What kind of damage could be expected? Where are other major areas of earthquake activity? These and other aspects of earthquakes will be discussed at the “All About Earthquakes” seminar, which will be held May 9 from 6 to 7:30 p.m. at the Morgan County Extension Office, 104 North Westgate, Jacksonville.
Registration cost is $5 per person, or free for Master Gardeners and Master Naturalists. Those interested in attending can call 217-243-7424, or register online at http://go.illinois.edu/earthquake.