HUMBOLDT COUNTY, CA — A 4.5 magnitude quake shook close to Petrolia on Wednesday afternoon, according to the U.S. Geological Survey.

The tremor rattled the area at 7:36 p.m. (6:36 p.m. local time). It occurred at a depth of 6 miles with the epicenter about 38 miles west of Petrolia. The magnitude was originally reported as 4.3 but later upgraded to 4.5.

Did you feel it?

If you felt the earthquake, you can share your observations using the USGS Felt Report form. The agency has received 31 responses on its online form so far, from people reporting they experienced weak shaking. Residents reported feeling the quake in a number of cities, such as Santa Rosa, Bayside, McKinleyville, Arcata and Whitethorn according to the USGS DYFI report.

Impact and estimated losses

The USGS categorized this as a Green Alert, which means there is a low likelihood of casualties and damage. Recent earthquakes in this area have caused secondary hazards such as landslides and liquefaction that might have contributed to losses.

Structure information summary
Most structures in this region are resistant to earthquake shaking, though vulnerable structures exist. The predominant vulnerable building types are unreinforced brick masonry and reinforced masonry construction.

Tremors last week

During the past week, there have been five quakes with a magnitude 2.5 or above centered nearby. The strongest, a 5.1 magnitude quake, was detected in the same region on Jun. 3.

The five largest earthquakes nearby from last week:

• 5.1, west of Petrolia on June 3
• 4.5, west of Petrolia on June 3
• 4.0, west of Petrolia on June 3
• 2.9, west of Petrolia on June 3
• 2.8, west of Ferndale on May 28

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. Earthquakes 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 are most common in Alaska, California, Hawaii, Oregon, Puerto Rico and Washington, according to the Department of Homeland Security.

It is estimated that there are 500,000 detectable earthquakes in the world each year. 100,000 of those can be felt, and 100 of them cause damage.

What to do during an earthquake

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.”

Source: The U.S. Geological Survey