for National Geographic News
A hundred years ago a massive earthquake reduced much of the San Francisco Bay Area to piles of smoldering rubble.
As the anniversary of that disaster approaches, scientists are warning that the heavily populated California region has a 62 percent chance of a magnitude 6.7 or greater quake between now and 2032.
What's more, researchers believe that the Bay Area may be ripe for a prolonged period of frequent and violent shaking.
Mary Lou Zoback is a geophysicist with the U.S. Geological Survey (USGS) in Menlo Park, California.
In the 70 years prior to the 1906 earthquake, a temblor of at least magnitude 6 struck the region an average of every four years, she said.
But since the 1906 earthquake, the Bay Area seismic zone has been eerily calm. Now Zoback and other experts say the reprieve may be at an end.
"We may be reentering that cycle," Zoback said.
Magnitude is a measure of the energy released by a quake at its hypocenter, the point underground where movement first occurrs along a fault.
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