Science of the New Madrid Seismic Zone
Overview
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. 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. A map of earthquakes epicenters, however, reflects faulting at depth and shows that the earthquakes define several branches of the New Madrid seismic zone in northeastern Arkansas, southwestern Kentucky, southeastern Missouri, and northwestern Tennessee. Other relatively young faults, which are not necessarily associated with recent earthquakes, or the main seismicity trend in the New Madrid region, are shown in this map. It shows 20 localities where geologists have found and published their findings on faults or evidence of large earthquakes (from sand blows; see image to the right).
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