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Why aren't earthquake warnings better?
01:38 - Source: CNN
CNN  — 

Aftershocks from the northern California earthquake rumbled through the Bay Area early Tuesday, the U.S. Geological Survey said.

One was a 3.9 magnitude aftershock that struck near American Canyon.

It was the largest since the 6.0 quake hit in the same area early Sunday.

Dozens of people were injured in Sunday’s quake, which caused at least $1 billion in property damage in Napa and other communities.