More than 3 million residents got early earthquake warning: 'A really big success'

More than 3 million people were notified by phone early Tuesday of a 6.4 magnitude earthquake that shook Northern California.Depending on their distance from the quake's epicenter - which was about 7.5 miles southwest of Ferndale - many residents were informed of the coming tremors before the shaking began, according to Robert de Groot, part of the U.S. Geological Survey's ShakeAlert operations team.

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