大发

Earthquake Myths and Facts

Earthquake Mythology or... Don't Believe Everything You Hear!

If the Earth moves beneath our feet, is it because Atlas shrugged? In a bygone era, some folks may have believed that theory, but even today there are earthquake anecdotes that aren't exactly the stuff of modern science. Let's take a look at them:

• Dogs and other animals can "sense" when an earthquake is going to strike
   It's impossible to determine whether a dog is behaving in an unusual manner because it smells an earthquake coming or a cat across the street. Changes in animal behavior sometimes have been observed prior to earthquakes, but that behavior is not consistent, and sometimes there's no perceptible behavior change prior to an earthquake.
• Earthquakes occur during "earthquake weather."
  The common misconception that earthquakes occur during hot and dry weather dates to the ancient Greeks. Earthquakes take place miles underground, and can happen at any time in any weather.
• Big earthquakes always occur early in the morning.
  Just as earthquakes don't care about the weather, they can't tell time. The 1940 Imperial Valley quake was at 9:36 p.m., the 1989 Loma Prieta quake at 5:02 p.m. People who perpetuate the time and weather myths tend to remember the earthquakes that fit the pattern and forget about the ones that don't.
• California could fall into the sea because of an earthquake.
  The San Andreas Fault System is the dividing line between two tectonic plates. The Pacific Plate is moving in a northwesterly direction relative to the North American plate. The movement is horizontal, so while Los Angeles is moving toward San Francisco, California won't sink. However, earthquakes can cause landslides, slightly changing the shape of the coastline.
• The ground can open up and swallow people.
  You've seen the image in books, movies and TV shows. That's not how it works. If a fault could open up, there wouldn't be any friction. Without friction, there's no earthquake. But earthquakes cause settling and other ground deformation that can include open fissures into which people, cars, etc., can fall.
• The safest place to be in an earthquake is under a doorway.
  That's true only if you live in an unreinforced adobe home. In a modern structure the doorway is no stronger than the rest of the building. Actually, you're more likely to be hurt (by the door swinging wildly) in a doorway. And in a public building, you could be in danger from people trying to hurry outside. If you're inside, get under a table or desk and hang on to it.
• Small earthquakes keep big ones from happening.
  Each magnitude level represents about 30 times more energy released. It takes 30 magnitude 3s to equal the energy released in a magnitude 4, 900 magnitude 3s to equal a magnitude 5 ... and 729 billion magnitude 3s to equal a single magnitude 9. So while a small quake may temporarily ease stress on a fault line, it does not prevent a large temblor.
• The magnitude of an earthquake determines whether disaster assistance is forthcoming.
  A magnitude 7 quake in the middle of the desert is likely to do less damage than a magnitude 6 in downtown Los Angeles or San Francisco. It is the magnitude of the damage, not the earthquake, which determines the level of response.
• We have good building codes, so we must have good buildings.
  That's true -- provided you're talking about buildings constructed under current building codes. In the case of older buildings, retrofitting -- bringing the building up to modern standards -- is up to the building's owners. There are plenty of buildings in areas of California prone to seismic activity which were built under older codes.
• Earthquakes are becoming more frequent.
  Research shows that earthquakes of magnitude 7.0 or greater have remained fairly constant throughout the century and have actually decreased in recent years. However, since there are a greater number of seismological centers and instruments capable of locating many small earthquakes that went undetected in earlier years, it may seem as if there are more.
• There's nothing I can do about earthquakes, so why worry about them?
  It's true that earthquakes can't be stopped, but you can be prepared. You can prepare an earthquake kit (food, water, flashlight, etc.), practice "duck, cover and hold" drills at home with your family and at work, and develop an earthquake plan (where would you meet family members if you weren't together when an earthquake hit?).

Sources: California Geological Survey/California Geology, USGS, Arkansas Center for Earthquake Education and Technology Transfer, Governor's Office of Emergency Services, Federal Emergency Management Agency, National Science Foundation, Southern California Earthquake Center, American Red Cross, Center for Earthquake Research and Information/University of Memphis.