Seismologists Say New Madrid Seismic Zone is Still Active

Posted on January 25, 2014

Earthquakes in the New Madrid Seismic Zone compared to typical aftershock sequence


Four powerful earthquakes struck the central U.S. in 1811 and 1812. This region is known as the New Madrid Seismic Zone. One of the earthquakes was so powerful that the Mississippi River ran backwards for a few hours. Experts say there is also geological evidence of powerful earthquakes in the region around 1450 A.D. and 900 A.D.

Seismologists Morgan Page and Susan Hough of the U.S. Geological Survey recently investigated whether current quakes in the region could be aftershocks of large earthquakes that occurred 200 years earlier. They used extensive computer modeling of aftershock behavior to determine that earthquakes in the region are not aftershocks of the 1811-1812 quakes. This disproves the long-lived aftershock hypothesis. It means the New Madrid Seismic Zone is still active.

A USGS.gov press release says, "A debate has swirled in recent years, fueled in part by past studies suggesting that continuing New Madrid seismic activity could be the tail end of a long-lived aftershock sequence following the 1811-1812 earthquakes. If modern activity is an aftershock sequence, the argument goes, then there is no evidence that stress is currently building in the zone. Instead, Page and Hough conclude that the current level of activity must be the signature of active, ongoing processes that continue to generate stress in the region - stress that we expect will eventually be released in future large earthquakes. In other words, the New Madrid Seismic Zone is not dead."

The researchers published a paper, "The New Madrid Seismic Zone: Not Dead Yet," here in Science magazine. In the paper the researchers says, "Our results imply that ongoing background seismicity in the New Madrid region is driven by ongoing strain accrual processes and that, despite low deformation rates, seismic activity in the zone is not decaying with time."

Image: USGS, Data source: CEUS-SSC catalog