This is from Friday, Nov. 5, 1999 ARKANSAS DEMOCRAT-GAZETTE

Geologists look at seismic zone, see 'loaded gun'

KENNETH HEARD
ARKANSAS DEMOCRAT-GAZETTE

For the first time, geologists have taken a peek underground at damage caused by past earthquakes along the New Madrid seismic zone, part of which is in northeast Arkansas.
    They don't like what they see.
    Research of vertical ground movement conducted by Karl Mueller, a geological sciences professor at the University of Colorado-Boulder, indicates that a 7.5-magnitude earthquake could occur every 1,000 years.
    Scientists predict that there is up to a 70 percent chance that a 6.0-magnitude quake will strike along the seismic zone within the next 15 years. There's a 90 percent probability of a 6.0 tremor before 2040, according to the study.
    The research rebuts earlier research by a Northwestern University scientist who said the New Madrid seismic zone was becoming dormant.
    "We certainly think it's a hazard," Mueller said Thursday. "You're sitting on a loaded gun."
    The zone cuts through the Midwest, from Cairo, Ill., southwest to Marked Tree in Arkansas.
    The fault system is best known for its series of great quakes in 1811-1812 near New Madrid, Mo. Estimated magnitudes of the tremors ranged between 7.8 and 8.1. They were powerful enough to ring church bells in Boston and cause buildings to crack in Savannah, Ga.
    An offshoot of the fault, or lineament, shook northeast Arkansas and southern Missouri last month. Scientists said the epicenter of the 3.9-magnitude quake, the third-largest in Arkansas in 25 years, was near Middlebrook in northern Randolph County.
    A 5.0 quake rattled Marked Tree in March 1976, and a 4.3 earthquake was recorded in Blytheville in November 1996.
    Mueller dug 10-foot-deep trenches in Lake County in northwestern Tennessee, peered into them and created models of the fault zone. His findings were published Thursday in the journal Science. Peggy Guccione, professor of geology at the University of Arkansas at Little Rock, co-authored the report.
    "We wanted to figure how fast the surface of the earth was deforming," he said.
    Unlike faults along the San Andreas seismic zone, which are on top of the earth's surface, New Madrid faults are buried beneath hundreds of feet of Mississippi River sediment. Such faults can raise and lower the landscape without actually breaking the earth's surface.
    Mueller calls such land formations "blind-thrusts." The thrusts fold layers of rock beneath the surface as they absorb the upward energy released by earthquakes. The trenches offered a view of some of the earth's vertical movement.
    "We couldn't see this before," he said.
    By measuring the width of the folded layers of rock, Mueller determined that the fault has been slipping about 6 millimeters a year.
    Mueller has been able to record the aftershocks that still occur each year from the massive quakes nearly 200 years ago. Those aftershocks pinpoint the seismic zone and help direct Mueller in searching for land changes.
    "It's like shining a bunch of flashlights on the fault," he said.
    In April, Seth Stein, a Northwestern University geologist, said his research showed that the New Madrid seismic zone had "turned off."
    Stein used satellite and ground-based measurements to check movement along the New Madrid fault. He said movement ranged between zero to 2 millimeters a year. Because of the little movement, Stein thought that the fault system was becoming dormant.
    He said his findings revealed that the 1811-12 earthquakes weren't as violent as scientists first believed. Stein estimated that the quakes may have been at 7 magnitude instead of higher.
    The trenches show otherwise, Mueller said. "They suggest active uplifts," he said of the geological evidence he found. "We're still [looking] at it. We want to know more."
    Gary Patterson, a geologist with the Center for Earthquake Research and Information at the University of Memphis, said he was impressed with Mueller's study, the results of which confirm Patterson's beliefs.
    "It's hard to refute his findings," Patterson said. "The general outlook is that the hazard hasn't been reduced.
    "He did good work."
   

This article was published on Friday, November 5, 1999