A 6.2-magnitude earthquake off the coast of Northern California has spawned dozens of aftershocks overnight, the U.S. Geological Survey reports.
The 6.2-magnitude quake struck at 12:10 p.m. Monday, December 20, in the Pacific Ocean 45 miles southwest of Eureka near the town of Petrolia, The Sacramento Bee reported. Damage and injuries were minimal.
More than 4,200 people from as far away as San Francisco and the Sacramento Valley reported feeling the quake to the USGS, the agency reported.
More than 40 aftershocks have followed the 6.2-magnitude quake on sea and land around Petrolia and Ferndale in Humboldt County, the USGS reported.
The aftershocks range from below 1.0 magnitude to as high as 4.5 magnitude, the agency said.
Seismologist Lucy Jones wrote on Twitter that the 6.2-magnitude quake and aftershocks appear unlikely to be forerunners to an even larger earthquake.
“Today’s quake is on the Mendocino fracture zone near where the Cascadia subduction zone comes to the Earth’s surface,” Jones wrote. “This is NOT where a quake on Cascadia will begin. Big quakes usually start at the deepest point on the locked fault and that is somewhere east of the Coast.”
“It has been a busy day for earthquakes on the Redwood Coast,” the California Geological Survey reported December 20 on Twitter.
“This latest USGS map shows 59 earthquakes today, with the largest aftershock coming in at M4.5. This aftershock behavior is not unusual and is a good reminder that, if you feel shaking, to ‘Drop, Cover and Hold On,’” the post read.
The aftershocks unnerved some California and Oregon residents, however.
“When you’re an Oregonian and feel an aftershock from an earthquake in Northern California for once,” read one Twitter post.
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.