Seconds before a 6.2 earthquake rattled California, phones got a vital warning

In the moments before a 6.2-magnitude earthquake struck the northern California coast on Monday, roughly half a million phones began to buzz. An early-alert system managed by the US Geological Survey sent warnings out before the ground started to shake, giving residents in the sparsely populated area vital time to take cover.

That left only about 25,000 people in the range of strong or very strong shaking, according to the US Geological Survey, though residents as far away as Sacramento and the San Francisco Bay Area reported feeling trembling.

Jane Dexter, manager of the Petrolia General Store, told the San Francisco Chronicle the rumbling and shaking had lasted for about 20 seconds. Glass bottles fell off the shelves at the store, bursting on the floor, but no one was hurt, she said.

There have been dozens of aftershocks ranging from 2.6 to 4.5 in magnitude, according to the USGS, through Monday and Tuesday. Though the quake originated off the coast, it did not trigger a tsunami and the National Weather Service announced that there was not a threat of one.

The Associated Press contributed to this report