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SECTION 2
THE NATURE OF
THE EARTHQUAKE THREAT

OBJECTIVE

To present information on the history, consequences, and existing threat of moderate to major earthquakes in Arkansas.

When people know what to expect in an emergency, even if only in general terms, they tend to react in a more reasonable, coherent manner. It is very important, therefore, to present realistic, believable expectations about earthquakes.

As educators, take advantage of the natural laboratory we live in. There are all kinds of lessons we can learn from earthquakes -- lessons in history, political science, urban planning, physics, and geology. You are educating children who may be able to make a difference in the future as engineers, seismologists, legislators, policy analysts -- all of whom can play a vital role in making our environment safer.

The magnitude 7.1 Loma Prieta earthquake (October 1989) provides us with an excellent example of the types of problems that arise in a major earthquake.

Following are some of the "geologic lessons" learned or reaffirmed from the Loma Prieta earthquake:

• There were no known short-term precursors to warn of the impending quake.
• The intensity of ground shaking was affected by local soil conditions. Damage in the Marina District in San Francisco and to structures such as the Bay Bridge and the Cypress section of Interstate 880 was enhanced due to poor soils in these areas.
• Seismic shaking triggered many landslides in areas of steep unstable slopes. The landslides damaged buildings and blocked many highways and roads.
• Damage to structures with adequate foundations on good ground was minimal. Serious damage was primarily restricted to older buildings and homes that predate recent building code changes.

The last damaging earthquake in the New Madrid Fault was on October 3 1, 1895. The epicenter was located near Charleston, MO at 39.0° N, 89.4° W. It was about a 6.2R episode.

Prior to that on January 5, 1843 a 6.0R earthquake occurred at or about Marked Tree, AR.

But the greatest recorded earthquake events occurred during a three month period of December 16, 1811 through March 15, 1812.

These were listed as follows:

In addition, there were approximately 2,012 earthquake events in the New Madrid Fault occurring during that period of time:*

5 were about 7.7R
10 were about 6.7R
35 were about 5.9R
65 were about 5.3R
89 were about 5.0R
1,800 were between 3.0R to 4.5R

The fact that the New Madrid Fault is now much closer to densely populated areas means that damage and loss of life from similar quake sizes will be much greater.

It is inevitable that there will be damaging earthquakes in Arkansas, but they need not be major catastrophes. You hold some of the keys to reducing the risk posed by earthquakes, both in terms of making our schools safer places now and educating our children to understand and live wisely with earthquakes.

KEEP IN MIND

• Don't paint too gloomy a picture of potential earthquake damage. Keep it moderate and believable. People tend to lose motivation if they believe the only damaging earthquake is a catastrophic one.

• Try to tie these activities to student preparation for a damaging earthquake as well as to the existing earth science curricula.

• Staff, students and parents all should receive earthquake information. Remind staff that they need to have an earthquake plan at home so that they can -confidently remain at school. Communicate your plans to parents and encourage them to develop plans at home as well.

• Consider, if appropriate, bringing in an expert to discuss the earthquake threat with staff, or use video or slide shows to illustrate the threat.

ACTIVITIES

1. Use the attached situation cards to guide a discussion with staff about what would happen at your school in the event of an earthquake.

2. Review The Earthquake Threat of the New Madrid Fault and discuss the nature of the earthquake threat with staff. Identify how an earthquake could affect staff in terms of ability to get to work, to get home, etc.

 

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School Earthquake Preparedness Guide - State of Arkansas
Arkansas Office of Emergency Services, 1993