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Big quake on Northern California coast follows cluster of smaller tremors farther south

A 5.5-magnitude earthquake hit off the Northern California coast about 60 miles west of Petrolia, the U.S. Geological Survey reported.

The tremor struck at 11:44 a.m. Sunday, May 21, according to the agency.

Nearly 100 people from as far away as Fort Bragg and Mendocino reported feeling the tremor to the agency.

The California Office of Emergency Services said on Twitter that it is working with local, state and federal authorities to assess damage from the earthquake.

Petrolia is a community of a few hundred people about 250 miles north of San Francisco.

Earlier Sunday, a series of quakes reaching up to 4.3 magnitude rattled the California-Nevada border near Big Pine, the USGS reported.

What to know about earthquakes

Magnitude measures the energy released at the source of the earthquake, the U.S. Geological Survey says. It replaces the old Richter scale.

Quakes between 2.5 and 5.4 magnitude are often felt but rarely cause much damage, according to Michigan Tech. Quakes below 2.5 magnitude are seldom felt by most people.

Earthquakes’ sudden, rapid shaking can cause fires, tsunamis, landslides or avalanches. They can happen anywhere, but they’re most common in Alaska, California, Hawaii, Oregon, Puerto Rico and Washington, according to the Department of Homeland Security.

If an earthquake strikes, it’s best to protect yourself right away. Here are tips from experts:

  • If you’re in a car: Pull over and stop. Set your parking brake.

  • If you’re in bed: Turn face-down and cover your head with a pillow.

  • If you’re outdoors: Stay away from buildings. Don’t go inside.

  • If you’re inside: Stay and don’t run outdoors. Stay away from doorways.

The best way to protect yourself during an earthquake is to drop, cover and hold on, officials say.

“Wherever you are, drop down to your hands and knees and hold onto something sturdy,” officials say. “If you’re using a wheelchair or walker with a seat, make sure your wheels are locked and remain seated until the shaking stops.”

Be sure to cover your head and neck with your arms, and crawl under a sturdy table if possible. If no shelter is available, crawl to an interior wall away from windows.

Once under a table, officials say you should hold on with one hand and be ready to move with it.

“There can be serious hazards after an earthquake, such as damage to the building, leaking gas and water lines, or downed power lines,” officials say. “Expect aftershocks to follow the main shock of an earthquake. Be ready to Drop, Cover, and Hold On if you feel an aftershock.”

How are earthquakes triggered and how are their magnitudes measured? What to know