An earthquake Thursday night was large enough to trigger shake alert warnings on people's smartphones in Northern California. The alerts are part of an earthquake warning system that are sent out when quakes reach magnitude 4.5 or higher, and are designed to give people time to take cover. "It was actually the first time that we've been able to use, on this scale, California's earthquake early warning system," said California Office of Emergency Services spokesperson Brian Ferguson. The early warning system goes through the MyShake app, which California first rolled out in October of 2019. See more in the video above.