Threat Looms of Greater Quake to Come

Seismologists warn that Northern California's biggest earthquake in 25 years may mean that a bigger one will hit soon.
1:51 | 08/24/14

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Transcript for Threat Looms of Greater Quake to Come
quarter century of relative seismological quiet in this part of California, and there are now worries that it might be a sign of bad things to come. Here's ABC's bazi kanani on the science of this quake. Reporter: The earthquake jolting northern California today struck more than six miles beneath the Earth's surface somewhere between these two fault lines, the Hayward Rodgers and the Concord green. This type of quake called a strike slip when two parts of the Earth's crust slide sideways against each other. This morning, California's early warning system gave scientists in Berkeley this ten-second warning before the quake. They're still just testing the system but hoping that one day everyone could get this critical alert. The last such major quake in northern California 25 years ago when the 7.1 Loma prieta quake brought down part of the San Francisco bay bridge. Just five months ago, a 5.1 quake near Los Angeles shook shelves, triggered a rock slide and burst water mains. Nearly all of California in the danger zone for a big one. In fact, scientists say the state has a 99% chance of a quake 6.7 magnitude or greater in the next 30 years. The 1994 northridge earthquake that killed nearly 60 and injured 5,000 was a 6.7. Researchers now using simulators like this fake trembler to test how earthquake-resistant construction stands up to a quake that size. Seismologists are warning people in northern California about the danger of aftershocks, 55 of them recorded already, and there is still up to a 10% chance that today's quake could be a foreshock meaning an even bigger quake could come within a week. Dan. Not what people in that part of the world want to hear. Bazi, thank you.

This transcript has been automatically generated and may not be 100% accurate.

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