California Waits For The Big One
Boogy-boarding down a flight of stairs during an earthquake is not a wise thing to do. Just ask Jewel McGuinnes, 12, of Eureka, California.
"A friend and I were at my house and we were boogy-boarding down the stairs," says Jewel. "About halfway down, tremors knocked me off my board. Next thing I knew, I was sitting at the foot of the stairs and my friend was screaming, 'Earthquake!'"
The quake that knocked Jewel off her boogy board last April has been followed by even bigger quakes. On June 28, 1992, the most powerful quake to hit the U.S. in 40 years struck Landers, California. It measured 7.4 on the Richter scale. Hours later, another big quake hit Bear Valley, 20 miles away. The two quakes caused one death and millions of dollars in damage. If the quakes had struck a big city, such as Los Angeles, the toll would have been higher. The quakes, say scientists, are just a reminder of "the Big One" still to come.
Earthquakes: Slips And Faults
The Big One is the name that scientists have given to a severe earthquake expected to strike California within the next 30 years.
What causes earthquakes? Scientists explain that the earth's crust, or outer shell, is made up of massive slabs of rock called plates. These plates, which can be as big as a continent or as small as a city, are constantly shifting. You can visualize the shifting of these plates by looking at what happens when Arctic ice floes meet each other. Some floes break apart, some slide partially over the other, and some simply grind past each other.
Most earthquakes occur along a fault — a crack in the earth's crust. One of the most visible is California's San Andreas Fault, where the Pacific Plate slides past the North American Plate. When two plates slip by each other, tremendous tension builds up. The tension is released in violent jerks or shock waves, which we call an earthquake.
The Big One; still waiting on the evening of October 17, 1989, residents of San Francisco thought that the Big One had struck.
Minutes before the start of the third game of the World Series between the Oakland A's and the San Francisco Giants, the city was rocked and rattled by a magnitude 7.1 earthquake. Buildings and bridges collapsed, fires broke out, and 59 people were killed.
Scientist later said that this quake was not the Big One. In fact, the 1989 San Francisco quake may seem like small potatoes when compared to the huge quake that scientists predict is to come.
What makes the Big One such a threat, says geologist Virgil Frizzell, is that it probably will occur in or near a major city in northern or southern California. Two likely candidates are San Francisco and Los Angeles. Such a quake would cause much more damage than the 1989 San Francisco quake. That quake, says Frizzell, had its center at a location 100 kilometers from San Francisco.
Not just in California about 40 moderate and thousands of minor earthquakes occur every year. "Remember, it's not just in California that earthquakes happen," Frizzell says. "They are happening every day, all over the world."
There is nothing that people can do to control the destructive power of an earthquake. But there are steps that we can take to limit the amount of damage and danger from an earthquake.
Making building codes tougher is one way to limit damage. By requiring builders to use safer materials and construction methods, much of the damage from quakes can be prevented. Homeowners can make their homes safer during a quake by securing water heaters, cabinet doors, and gas lines.
Do Californians like Jewel worry about the Big One? "Well (after the April 25 quake), I was scared to go to bed," Jewel says. "Since then, whenever I feel a tremor, I get worried. But more than anything, I am much more on my toes, much more aware."
Richter Scale - Typical Damage:8 - Total damage. 7 - Buildings collapse. 6 - Buildings crack and things fall off shelves. 5 - Furniture and pictures move. 3-4 - People feel a rumble and hear noise. 1-2 - Most people do not notice anything.
Septermber 4, 1992