Punctuated earthquakes for New Madrid area: New research uncovers cluster of past events

phys.org | 11/6/2018 | Staff
MysticHeart (Posted by) Level 3
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Christopher DuRoss of the USGS updates maps of the trench walls while sitting on one of the benches excavated across the sackungen. Flags on the wall denote different layers of sediment the team identified that moved during past earthquake events. Credit: Ryan Gold.

In 1811 and 1812, the region around New Madrid, Missouri, experienced a number of major earthquakes. The final and largest earthquake in this sequence occurred on the Reelfoot fault, and temporarily changed the course of the Mississippi River. These earthquakes are estimated to be just shy of magnitude 8.0 and devastated towns along the Mississippi River—soil liquefied, houses collapsed, and chimneys toppled.

Earthquakes - New - Madrid - Area - Zone

Because of the 1811-1812 earthquakes, the New Madrid area is recognized as a high-hazard zone for potential future seismic events. Previous investigations found have also found evidence for multiple, older earthquake events preserved in the geologic record.

"We know there were also large earthquakes at ~1450 AD and at ~900 AD," says Ryan Gold of the U.S. Geological Survey (USGS), but frequent earthqakes along the fault may not be the norm.

Earthquakes - Reelfoot - Fault - Years - Hundreds

"If earthquakes happen on the Reelfoot fault every 500 years, and have been doing so for hundreds of thousands of years, we would expect to see a mountain range there—but we don't," says Gold. Instead, he suggests the modest fault scarp associated with the Reelfoot fault indicate that the earthquakes haven't been sustained over a long period of time.

To test this, USGS researchers wanted to look beyond the last few thousand years. Preserving long-records of past earthquakes can be a challenge for the Reelfoot fault because natural processes like rain and occasional floods on the Mississippi River can conspire to erase the record of past earthquakes. "That's coupled with anthropogenic effects—lots of farming, forestry, [and] construction," says Gold.

Fault - USGS - Team

Instead of studying the fault directly, the USGS team moved to...
(Excerpt) Read more at: phys.org
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