Scientists debate risk of major quake

Some say it's not a matter of if; it's when.
CHICAGO TRIBUNE
GRAND TOWER, Ill. -- Nearly 200 years ago, catastrophic earthquakes caused the Mississippi River to flow backward, triggered landslides and floods, leveled houses, killed scores of settlers across the Midwest, and clanged church bells as far away as Boston.
Now, as the nation struggles with recovery and learns lessons from Hurricanes Katrina, Rita and Wilma, there are new warnings that the Midwest is vulnerable to and unprepared for a natural calamity. The ground beneath America's heartland has been rumbling in greater frequency and magnitude in recent months, leading government officials to shudder at the region's susceptibility to severe damage and casualties.
Midwesterners may not know it, but there are active fault lines deep beneath America's heartland.
Five mild quakes registering magnitude 3.0 and higher have jolted the five-state region around southern Illinois since February. They're the highest in repeating intensity in about the last quarter-century. One of the strongest jolts came in early June in farmland around this small Illinois community west of Carbondale. Several other strong jolts were felt in recent months in Kentucky, Tennessee, Arkansas and Missouri.
"Have you ever seen a floor roll?" asked James Lloyd Todd, 67, who lives in northern Tennessee and felt a 4.0 earthquake centered nearby in June, one of the strongest in decades. "I can't remember shaking that bad."
Shifts in terrain
Adding to the jitters, the journal Nature published a recent study from the University of Memphis showing minute shifts over the past five years in the Midwest terrain. It's a possible indicator of underground pressure buildup that triggers earthquakes, researchers say.
What it all means, though, is under debate. While disagreeing over the significance of recent ground movement, geologists still caution against alarm and say the region is unpredictable when it comes to earthquakes. In an area prone more to flooding and tornadoes, a major earthquake remains a far less likely possibility, geologists say.
"A lot of what we are seeing is hype out of proportion," said Seth Stein, a Northwestern University geologist who has studied the region. "Just because we have a little shaking now and then doesn't mean everyone should get all excited."
Still, based mostly on history and emerging data, some geologists estimate there is a 25 percent to 40 percent chance of a magnitude 6.0 earthquake striking again in the next 50 years -- enough to do significant damage from St. Louis to Memphis.
Public warnings
A Southern Illinois University geophysicist and an SIU radio and television professor have crafted public service announcements to begin airing next month warning of the potential hazards of earthquakes. They hope to also begin airing the spots on PBS stations elsewhere in the New Madrid region.
"It's not a matter of if; it's when," said Sue Evers, who coordinates regional earthquake preparedness for the Federal Emergency Management Agency in Kansas City, Mo. "We are certainly seeing major accelerations in frequency and size. They are wake-up calls."
For the most part, Midwesterners pay little mind to the occasional shaking that has been going on for almost two centuries.
One afternoon in December 1811, the earth here shook so violently the Mississippi River ran backward, overflowed its banks, and sent waves of water and silt over farmland for miles around before eventually forming its current course.
Several major earthquakes followed the next year. Although there was no measuring stick in the 1800s, scientists analyzing historical accounts believe they were the most intense in American history and consisted of some 2,000 aftershocks.
Shaky buildings
But as the Midwest population grew, earthquakes became a distant point of history. From sprawling cities to tiny towns, most structures since the 1800s have been built of unreinforced masonry and brick construction that would crumble during a 6.0 quake.
Building codes safeguarding against earthquakes in the Midwest are inconsistent. Missouri and Illinois have no state standards, leaving it up to counties and communities to decide. For the most part, only modern high-rise and public buildings in the Midwest have been constructed using a 1990s-era building-industry standard designed to resist such an earthquake.
In recent months, though, federal and state officials have been pressing for more stringent and uniform building codes as scientists' studies warn of possible stronger quakes. But changing the codes often involves a lengthy communitywide process. Stricter codes also mean higher building costs and millions of dollars spent to retrofit buildings.