ORANGE (CBSLA.com) — The warning of a big earthquake hitting Southern California Tuesday has many shaken up and stocking up.

The U.S. Geological Survey said an earthquake with a 7.0 magnitude or greater could strike by Tuesday.

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The chance of a mega-quake went up after a swarm of small quakes near the San Andreas Fault rattled the Salton Sea over a week ago.

The risk is temporarily elevated to 1 percent above normal.

In a rare move, San Bernardino city officials have shut down their city hall for a couple days until the risks subside. The building doesn’t meet seismic standards.

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The warning prompted some to stock up on emergency supplies including 55-gallon drums of water.

Dave O’Brien, who works at an army supply store in Orange, said since the alert was issued, small waters, energy bars, three-day food kits and survival kits for the car are selling out.

“We have an additive that will give it (water) a five-year shelf life. But right now, we are out of it,” he said. “They’re concerned about not being able to get to any food or water the next two weeks.”

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Emergency supply websites, like Sunset Survival, said business has tripled in the last week.