Quake up call.

Shaken by the recent earthquake, a Los Angeles teen wonders if a Big One is coming her way.

On January 17, at 4:31 A,M., Jennifer Blostein was jolted from her sleep. "My house alarm goes off and I hear this rumbling. My bed was shaing," recalls the fourteen-year-old from Northridge, CA. "I tried to get out of bed... The floor was covere with glass. It was commpletLy dark. I was holding onto my doorway for dear like."

Although the magnitude 6.7 earthquake lasted less than a minute, "it felt like eternity," she tries to look at the bright side. "We're safe. Our house is safe. And we're just going to try to get back to our daily lives."

But checking out her neighborhood, Jennifer knows that's easier said than done. "There's threat of disease from [leaking] sewage," she says. "I'm worried about the people without homes," some 11,000 Los Angeles residents who (as of this writing) are sleeping in tents or in emergency shelters, including the gym at Jennifer's school. According to recent reports, the quake killed 61 people and injured more than 9,000 others. The damage could total $20 billion, officials say.

FAULT CITY

"They say this isn't the '!ig one,'" Jennifer says. "But then what is?"

The so-called Big One, scientists predict, wikll be a magnitude 8.0 earthquake that could occur sometime in the next 30 years along the San Andreas fault, a massive slash in Earth's crust that runs the length of California (see map, p. 12). This fault marks the boundary between two slabs of crust, called tectonic plates, which grind past each other in opposite directions.

Any Californian can tell you that the San Andreas is an earthquake breeding ground. The 1989 San francisco quake, for one, occurred along a 40-mile segment of the fault.

But the recent L.A. quake didn't strike along the San Andreas. It struck a smaller, previously unknow, fault about 96 km away and 14.8 km beneath the ground Esee diagram, above). When rocks on either side of the fault tried to grind past each other, they built up a lot of stress. Enough pressure grew until--CRACK! --the rocks lurched past each other. The burst released lots of pent-up energy through the ground in the form of violent vibrations: an earthquake.

This newly discovered fault is one of hundreds of small cracks in Earth's crust that zig-zig on either side of the San Andreas. These faults form when stress from the moving plates gradually cracks the surrounding earth.

The high number and position of these faults beneath heavily populated areas has many scientists in a tizzy. "We're not just concerned about the Big One" along the San Andreas, says seisomologist James Dolan. He and other scientists worry that if many of these smaller faults give way all at once, they could release enormous amounts of energy and cause several major quakes--perhaps hundreds of times more powerful than the L.A. quake.

For L.A. residnets--or anyone who saw the startling news reports of the recent quake--a bigger shakeup might be hard to imagine. After all, the energy released from this past quake was enough to wreck highways, burst water and gas pipes, and destroy thousands of homes. It even forced a nearby mountain range to "grow" taller by more than a foot. Jennifer and other Angelenos are still shaking from the quake's aftershocks, thousands of smaller tremors that may continue for years.

TAKING COVER

To calm fears and increase preparedness, scientists are working on experiments to predict earthquakes (see SW 2/12/92, p. 7). But these test are still in their early stages, says seismologist David Oppenheimer.

In the meantime, people just have to buckle down and be prepared. Californians know what to do: Stock water and food; keep a first-aid kit, flashlight batteries, and a radio on hand.

Despite California's shaky ground, Jennifer plans to stay there for good. "Some people may think I'm crazy," she says. "But what can you do? In florida they have hurricanes. Tornadoes are everywhere. You have blizzards in New York and New Jersey.... California has earthquakes." Plus, she adds, "It's the only home I've known."