Public Power - November 2008 - (Page 41)

EARTHQUAKE: The Hidden Disaster Out ofinclement weather, anInonlooker can sight, out of mind. the lead up to most see the approaching tornado, hurricane or ice storm. An earthquake is a different matter, especially given the rarity of strong earthquakes that feel like anything more than construction in the distance. Lacking visual stimuli to remind them of the natural disaster’s threat, people may take precautions for weather conditions (storm shelters, evacuation routes, and supply stockpiling), but fail to prepare for the possibility of an earthquake. This attitude is unwise for most of the United States, where only North Dakota, Minnesota, Wisconsin and Florida are considered completely seismic-free. Most vulnerable—and most populous—are the Northeast, Southeast, Midwest, and the states west of the Rocky Mountains. The rarity of strong earthquakes in the Southeast and the Midwest should not obscure the fact that their seismic zones have the capacity for disastrous earthquakes. The East Tennessee Seismic Zone (the Appalachian Seismic Zone) is capable of producing a magnitude 6 earthquake and the New Madrid Seismic Zone, covering parts of Illinois, Indiana, Kentucky, Tennessee, Mississippi, Arkansas, and Missouri, produced three magnitude 8 earthquakes in 1811 and 1812. Seismologists estimate that earthquakes of this magnitude occur on average every 400 to 600 years. However, there is no way of knowing whether the next “big one” will occur tomorrow or hundreds of years from now. One thing that seismologists do agree on is that it is not a question of if, but when. Experts estimate that every 75 to 100 years the New Madrid Seismic Zone produces an earthquake of about 6.0 magnitude—powerful enough to do significant damage. The last one was 1895. “We’re overdue,” said Jim Wilkinson, executive director of the Central United States Earthquake Consortium in Memphis, Tenn. The Wabash Valley Seismic Zone, which www.APPAnet.org includes three of the seven states that are also in the New Madrid zone, is capable of producing magnitude 7 earthquakes, which is stronger than was estimated even a few years ago. “The Wabash erupted with a 5.2 in April 2008 that was felt in 12 to 14 states, and caused damage in three,” said Wilkinson. And, of course, there is California, where dozens of earthquakes rock the region on a daily basis. In fact, it may be the only state where people think about earthquakes more often than weather disasters. Earthquakes in the Midwest are harder to predict than in California because Midwestern quakes occur miles below ground, covered by loose soil. About 200 minor earthquakes occur each year in the New Madrid zone, most of them are too weak to be felt by humans.) In California, the faults are visible on the surface, and motion detectors can be set up to measure fault movement, which can aid in prediction. The loose soil in the Midwest causes another problem. For example, while a magnitude 5 earthquake in California might cause shaking in one or two counties, an earthquake of similar magnitude in the Midwest can cause shaking across several states because shockwaves travel through the soil from deep under ground. The earthquakes of 1811-1812 that occurred in Missouri were felt on the Eastern Seaboard. “A powerful earthquake in the New Madrid zone would have a regional impact, not just a community impact, and we see it as a very serious threat,” said Wilkinson. “There would be a direct impact to utility generation, transmission, and distribution.” There would also be an indirect impact, such as curtailed coal supplies as a result of railroad track and bridge damage or destruction. “Barge traffic carrying coal to power plants near the Mississippi River would also probably come to a halt,” he said. The soil near the river is more vulnerable to shaking. In fact, much of the soil in the New Madrid zone can be subject to liquefaction BY WILLIAM AT KINSON “In California, the faults are visible on the surface, and motion detectors can be set up to measure fault movement, which can aid in prediction.” NOVEMBER-DECEMBER 2008 41 http://www.APPAnet.org

Table of Contents Feed for the Digital Edition of Public Power - November 2008

Public Power - November 2008 Contents Perspective 10 Questions Capturing Knowledge Before It Retires Jackson’s GIS Search Keeping a Job Journal Japan Tackles the Kyoto Protocol Getting to 20 by 10 Damless Hydro Power Earthquake: The Hidden Disaster For Engineers Safety For Governing Boards DEED Hometown Connections Parting Shot

Public Power - November 2008

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