- Published on Monday, 29 October 2007 00:10
The New Madrid Seismic Zone also is particularly susceptible to ground subsidence. During the ground-shaking of an earthquake, individual soil grains are rearranged to take up less space - much like cereal in a box when it is shaken. The settling tilts the land; forms cracks and fissures; and damages building, roads, bridges, and pipelines.
Because of different geologic characteristics, Midwestern earthquakes inflict more damage over greater areas than earthquakes of the same magnitude that occur on the West Coast.
Unlike the relatively uniform crust of the mid-continent, the complex and fractured rock of the West Coast tends to dampen seismic waves as they travel, thereby reducing the area of damage for an earthquake of a given magnitude.
Successfully predicting earthquakes is one of the goals of earthquake seismologists. Periodically, preliminary results of new prediction methods show some promise, but under rigid testing their reliability often fades.
A system of prediction widely used by seismologists is to analyze statistics of earthquake frequency in given areas. Although complicated, these studies are extremely helpful for long-range planning. In Missouri, they illustrate the serious risk presented by the New Madrid Seismic Zone.
Results of recurrence studies in southeast Missouri show that there is a 50 percent probability that a 6.5 magnitude earthquake will occur by the year 2000. Such an earthquake would have an intensity of MM IX near the epicenter. The last earthquake of that magnitude occurred near Charleston, Missouri in 1895 and caused serious liquefaction and other damage.
An ideal prediction system would foretell a destructive earthquake in time to allow governments, industries, and the public to take measures to reduce loss of life and property, but would not predict it so far in advance that people would flee an area weeks ahead of time, anticipating an event that might not happen. Most seismologists believe that within a few years they will be able to predict major earthquakes in a reasonable time.
In 1979, the Missouri Legislature passed the Dam and Reservoir Safety Act, which regulates the operation, modification, and construction of new dams 35 feet high or higher. The Department of Natural Resources’ dam and reservoir safety program works with the governor appointed Dam and Reservoir Safety Council to develop and enforce these regulations. Some regulations include design criteria specifically meant to make dams and reservoirs as earthquake proof as possible.
For the purpose of ensuring dam safety, the state is divided into six zones according to how intensely an earthquake is likely to shake the ground. The most stringent design criteria apply to dams in southeast Missouri, in contrast to those in the northwestern part of the state, where the threat of a major earthquake is relatively low.
After the 1971 San Fernando, California, earthquake killed about 75 people and destroyed health facilities, the nation became more acutely aware of the risk presented by earthquakes. Shortly thereafter, President Nixon established a commission to investigate seismic threats. Congress later appropriated money for the National Earthquake Hazard Reduction Program (NEHRP), which provided funding to the National Science Foundation, the U.S. Geological Survey, the Nuclear Regulatory Commission, the U.S. Army Corps of Engineers, and the U.S. Bureau of Standards.
Eventually, the Federal Emergency Management Agency (FEMA) was created and charged with responding to and mitigating all types of natural disasters. Public information and predictions of natural disasters also are part of FEMA’s responsibilities.
Because of the earthquake potential in the central United States, seven state have joined together to form the Central United States Earthquake Consortium (CUSEC). Its purpose is to enhance public awareness of the earthquake threat and to coordinate the earthquake preparedness planning effort in the central United States.
WHAT TO DO BEFORE AN EARTHQUAKE
Movement of the ground seldom is the actual cause of death or injury. Most casualties result from partial building collapses, falling objects and debris, like toppling chimneys, falling bricks, ceiling plaster, and light fixtures. Many of these conditions can be prevented by taking a few steps now to prepare.
- Place heavier objects on lower shelves to prevent breakage and personal injury.
- Bolt to walls anything that might topple, like top-heavy shelves, appliances, and furniture. Don’t hang heavy picture frames or mirrors over the bed. Don’t hang plants in heavy pots that could swing free of hooks.
- Strap your water heater to wall studs with metal plumbing tape to prevent broken pipes and fires.
- Locate master switches and shutoff valves for all utilities and know how to turn them off. Your local utility company can show you.
- Keep on hand a flashlight; a portable radio with fresh batteries; a first-aid kit; a fire extinguisher (Class C is designed to use safely on any type of fire, including electrical, grease, and gas); a three-day supply of fresh water; non- perishable, ready-to-eat foods; and an adjustable wrench for turning off gas and water.
WHAT TO DO DURING AN EARTHQUAKE
During a major earthquake, you may experience a gentle shaking that becomes violent in a second or two and knocks you off your feet, or you may be jarred first by a violent jolt - as though your house was hit be a truck. A second or two later, you feel the shaking and, as in the first example, it may be impossible to move from one room to another.
- Stay calm and stay put.
- If indoors, crouch under a desk or heavy table, or brace yourself in a doorway. Stay away from windows or brick masonry (like fireplaces), bookcases, china cabinets, and mirrors.
- If outdoors, stand away from buildings, trees, and power lines.
- If driving, move away from overpasses, stop slowly in a safe area, and stay in your vehicle. Stay off bridges. Listen to the radio.
- If in a high-rise building, stay in the building, on the same floor. Get under a desk and stay away from outside walls and windows. Do not use the elevator.
WHAT TO DO AFTER AN EARTHQUAKE
- Wear sturdy shoes to protect your feet from broken glass.
- Check for injuries and apply necessary first-aid.
- Check gas, water, electrical lines, and appliances for damage. If you smell gas or see a broken line, shut off the main valve. Do not switch on the gas or electricity again until the power company checks your home. Do not light matches, use any open flames, or turn on electrical switches or appliances until you are certain that there are no gas leaks.
- Check to see that sewage lines are intact before you use the toilet. Plug bathtub and sink drains to prevent sewage backup.
- Clean up spilled medicines, bleaches, gasoline, and other flammable liquids.
- Check for building damage and potential safety hazards, like cracks around chimneys or foundations.
- Be prepared for aftershocks, which can further damage weakened structures.
- Listen to the radio for public safety instructions.
- Do not use the telephone except in an emergency.
This article adapted from Vol. 1, No. 3, p. 3.