Wednesday morning thousands of cell phones buzzed as an urgent message about a “TEST of the CA Earthquake Warning System. No action required. THIS IS A TEST.” At 11 a.m. the first residential deployment if the states earthquake warning system went out to phones in a 60-block zone of Oakland.

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https://www.sfchronicle.com/bayarea/article/Thanks-for-the-heart-attack-earthquake-13720859.php