Southern California was rocked Monday morning by a 5.2-magnitude earthquake that struck close to San Diego.

The US Geological Survey reports that although the earthquake’s center was close to San Diego, shockwaves could be felt over 100 miles distant, all the way to Los Angeles.

“Hold on, cover, and drop.” As earthquakes shook roads and tall buildings, authorities issued an emergency alert to citizens, warning them to “protect themselves.”

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The epicenter of the earthquake was close to the town of Julian, northeast of San Diego, and it struck at around 10:08 a.m. local time.

According to the USGS, the earthquake had an intensity of IV on the Modified Mercalli Intensity Scale, which is strong enough to cause automobiles to wobble and windows to rattle. It felt like a “heavy truck hitting building.”

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