On Monday night, residents of the Los Angeles neighborhoods of Westwood, Los Feliz, Silver Lake, and parts of the San Fernando Valley experienced a mild earthquake—a magnitude 3.6. Most people slept through the temblor and no damage was reported. But a select group of 150 LA residents got a text alert on their mobile phone a full eight seconds before the quake hit at 11:10 pm—enough time for people to drop, cover, and hold on.

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