St. Louis Post-Dispatch Archives |Full text of archived story
| A WHOLE LOTTA SHAKIN' COMING ON? |
- Susan Hough, And Eugene Schweig
- St. Louis Post-Dispatch (MO)
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- July 1, 2002
- Section: EDITORIAL
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- Edition: FIVE STAR LIFT
- Page B7
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* EARTHQUAKES * BRACE YOURSELF: We can't stop earthquakes, but understanding more about them can help us prepare for the next "big one." The earthquake that struck near Evansville on June 17 may have surprised some Midwesterners, but long-time residents of the Wabash Valley region, along the border of Illinois and Indiana, may have felt a number of earthquakes over the years, including a magnitude 5.2 temblor in 1987. Although big enough to be widely felt, most earthquakes of magnitude 4 or 5 generate only harmless rumblings. It would be a mistake to conclude that all future Wabash Valley earthquakes will be so tame. The distribution of earthquakes in any region follows a simple mathematical pattern. In the Wabash Valley, this pattern suggests that magnitude 7 or larger earthquakes will occur every few thousand years. Magnitude 7? Little earthquakes once in a while are one thing, but magnitude 7? In Indiana or Illinois? But such events will happen in the future, not only because of mathematics but also because geological investigations provide compelling evidence of major earthquakes in the not-too-distant past. During a major earthquake, sandy soils can lose their internal cohesion and behave like a liquid. Sand typically gets forced up to the surface, creating "sand blows." Evidence of these features may remain in the ground for thousands of years, indicating through their size and distribution the magnitude of the earthquake that caused them. By combing river valleys, scientists from the U.S. Geological Survey and Indiana University have found evidence for about 10 strong earthquakes in the Wabash Valley over the past 12,000 years, the largest being possibly as large as magnitude 7.5, approximately 5,000 years ago. Earthquakes of this magnitude are big enough to cause substantial damage not just nearby but as far away as St. Louis and Chicago. Many Midwesterners are aware of large earthquakes in the past, especially the great New Madrid earthquakes of 1811-1812. This sequence included four earthquakes now estimated to have had magnitudes of at least 7.0 to 7.5. Most scientists consider the Wabash Valley to be within the zone of elevated hazard that includes New Madrid. New Madrid has experienced a higher background rate of small-to-moderate earthquakes since 1812, but this activity may represent long-term aftershocks from the 1811-1812 events. And both regions have experienced earthquakes bigger than magnitude 7 in the past 10,000 years. The New Madrid region was designated as a high-priority study region just over a decade ago by the U.S. Geological Survey, providing the resources and direction for multifaceted investigations that have improved significantly our understanding of the zone and the hazard it poses. These investigations have been matched by a growing awareness by the public and policy makers that, in turn, has led to steps toward hazard mitigation, including a program to retrofit schools and other critical structures. Many of these efforts are being led by the Central United States Earthquake Consortium, which includes seven Midwestern states. Such efforts have a ways to go before they catch up to California, where earthquake-resistant design and building codes have been a priority for decades. But New Madrid is ahead of other regions in the Midwest that are exposed to significant earthquake hazard but are not yet aware of it. And unlike New Madrid, the Wabash Valley is relatively sparsely monitored. We missed a golden opportunity to record the level of shaking throughout the Midwest, as is now done routinely in California. Plans are on the table for the Advanced National Seismic System, which will include 7,000 earthquake monitoring stations across the United States. When this system is fully operational it will improve substantially our ability to monitor earthquakes. Of course, monitoring earthquakes does not stop them. But experience in California and New Madrid clearly shows that improved scientific understanding provides the best impetus -- short of a catastrophic event -- for hazard mitigation. This process can be frustratingly slow, but, like any journey, it cannot be finished until it is begun. Californians know they live in Earthquake Country. But guess what? You do, too. ======== For more information about earthquakes go to: The Central United States Earthquake Consortium: www.cuse.org/about U.S. Geological Survey: http://pasadena. wr.usgs.gov/shake/cus/ Earthquake Hazards Program - Central and Eastern U.S.: www.ceri.memphis.edu/usgs/ Earthtquake Hazards Program - Northern California: http://quake.wr.usgs.gov
(1) PHOTO - For more information about earthquakes go to:
The Central United States Earthquake Consortium: www.cusec.org/about
U.S. Geological Survey: http://pasadena.wr.usgs.gov/shake/cus/
Earthquake Hazards Program -- Central and Eastern U.S.: www.ceri.memphis.edu/usgs/
Earthquake Hazards Program -- Northern California: http://quake.wr.usgs.gov
FIGHTING TERROR
(2) PHOTO - (cracked rock) GRAPHICS
(3) Graphic / Map - From Memphis to St. Louis - New Madrid Fault
The New Madrid Fault, the center of which is 175 miles south of St. Louis, is blamed for an earthquake in the early 1800's that made the Mississippi run backwards.
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