Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS
NATURE
NATURE Home Current Season Episode Index NATURE Shop Contact Us For Teachers
Video DatabasePuzzles & FunEpisode PreviewsAnimal Guides
Featured Program
Forces of the Wild
Flowers An earthquake A wave

Avoiding Destruction

Earthquakes are one of the most deadly -- and unpredictable -- forces of the wild. One earthquake that struck China in 1556 killed 830,000 people, making it one of the worst natural disasters of all time. More recently, the 1988 earthquake in Armenia killed 24,900. Naturally, scientists would like to find a way to predict the arrival of an earthquake, to warn those at risk and save lives. They are inching ever closer.


Earthquakes are one of the most deadly forces of the wild.
One of the most popular folkloric methods of predicting quakes is watching for changes in animal behavior. For more than 200 years, people have reported odd animal activity hours or minutes before a quake: snakes and lizards abandoning burrows, cattle moving to higher ground, unusually excited domestic animals, swarming insects, and deep-water fish moving to shallow areas. Some say that animals might be sensing changes in electromagnetic fields, but there have been no quantitative studies done, and most scientists remain skeptical.

Rather than rely on animal messengers, scientists are trying to use their own sensors to detect changes in the Earth that occur before an earthquake. As seen in FORCES OF THE WILD, Rich Liechti of the U.S. Geological Survey is monitoring the San Andreas fault, Californiaís most vulnerable seam, where it passes through the tiny town of Parkfield, California. Liechti and his colleagues have trained two video cameras on the fault, hoping to film what happens to the ground before, during, and after the next big earthquake. They have also set up numerous instruments to monitor changes in magnetic fields, water well levels, surrounding topography, and strain levels felt along the fault itself. They hope, says Liechti, "to see some major and consistent changes in the months before a quake, or even hours before a quake." Such changes could then be monitored in earthquake-prone areas around the world.

Parkfield is supposed to be an active earthquake area, with a major quake occurring along the fault there about every 22 years. But 10 years after the last quake was expected to occur, Liechti is still waiting. He's been waiting, watching, and collecting data for 12 years. "We're still sitting in the waiting room," he sighs. "It's like waiting twelve years for your baby to be born."

Scientists are doing some earthquake forecasting now, but the forecasts are rather broad. The quake hunters can say only that a quake has a certain chance of occurring within a given time frame, not that one will happen on, say, Tuesday the eighth at 4 p.m. The system is based on the fact that earthquakes rarely occur one at a time; they tend to occur in clusters of shocks of varying strengths, with most called foreshocks or aftershocks. Based on the patterns of fore- and aftershocks that have been identified in past earthquakes, scientists can now estimate the probability that more shocks will follow once one has been detected.

For example, in 1989, a small earthquake hit the area south of San Francisco. Government scientists warned that there was a one in 20 chance of a larger quake in the next 60 days, a much higher risk than the usual chances of one in 15,000. Nothing happened during the warning period, but just days after it ended, San Francisco was hit by a major temblor, the Loma Prieta quake, which killed 63 people and caused billions of dollars in damage.

The quake measured 7.1 on the Richter scale. The Richter scale measures the amount of energy released by an earthquake. It is an exponential scale, in which the increase from one whole number to the next means a tenfold increase in energy. Thus, the devastating 1906 San Francisco earthquake, which measured 8.3, was more than ten times more powerful than the 1989 earthquake at 7.1. Earthquake warnings, while they might not be specific enough to tell people to evacuate their homes at a certain time, do help emergency services to know when to keep extra personnel on hand and when it is more likely safe to enter damaged buildings without the threat of aftershocks.

Until a warning system is perfected, the only other option for people who are very worried about earthquakes is to move to North Dakota or Wisconsin: since their faults are very ancient, those states are the least likely to experience earthquakes.






Earth
Recipe for Life
Why did life evolve on Earth?
Lava
Volcanic Action
The secrets of erupting volcanoes.
Sunset
The Equinox
Why aren't our days and nights of equal length?
Lightning
Understanding El Niño
What is El Niño?
Earthquake
Avoiding Destruction
Meet an earthquake hunter.
Volcanic eruption
Timeline
Significant events in geological history.
Dandelions
For Teachers
View FORCES OF THE WILD lesson plans.
A bird
Resources
Web links and books related to the program.
Printe-mail

episode homepage