Expert Warns of Earthquake in New Madrid Zone
Gary Patterson, USGS
"This is not a California earthquake," Patterson said last week at a meeting of the Arkansas Gov.'s Earthquake Advisory Council. "There are some basic differences here that drive the hazard level up."
Patterson, who serves as information director and geologist for the Memphis center, said that, unlike faults in California, the New Madrid Seismic Zone contains three to five major fault segments lying over the top of each other in a relatively small area.
The zone stretches from northeast Arkansas and northwest Tennessee up into southeast Missouri, far western Kentucky and southern Illinois.
Big earthquakes have happened before and will happen again in this area, he said, citing the series of quakes in 1811-1812 that were the strongest ever to occur in the continental United States.
But he said even a 6.5-magnitude quake has the potential of doing an enormous amount of damage in Blytheville and Mississippi County, Patterson said.
"It won't take a catastrophic earthquake to do catastrophic damage," he said.
One of the most potentially damaging effects of an earthquake in this area, Patterson said, will be liquefaction of soil near the surface. Huge areas of sand in fields that are visible throughout the region are evidence of liquefaction in past earthquakes, he said.
Patterson said liquefaction is expected to happen mostly in the places where the Mississippi River has moved around, depositing sandy silt and gumbo clay. In these areas, the water table is 6 feet or less below the surface of the ground, and a quake will send the water to the surface, creating quicksand and eliminating the soil's ability to support loads.
During the first 72 hours after a significant quake of any magnitude, Patterson said people will need to be rescued from collapsed buildings. He said 11 million people live in the New Madrid Seismic Zone, and a response plan is needed to get "boots on the ground" during that period.
Patterson said he was recently visited by a Japanese diplomat who wanted to know if it was a good idea to build a truck plant in northeast Arkansas.
"It is a good idea when things are built to proper codes," he said. "The name of the game is building structural type. We all have to be on the same page when we talk to these people."