Ten earthquakes of preliminary magnitudes between 3.0 and 4.5 struck off the coast of Northern California between Saturday and Sunday, the United States Geological Survey reports.
The series of earthquakes rumbled beneath the Pacific Ocean, between 3 miles and 27 miles west of Petrolia in Humboldt County.
The first earthquake struck early Saturday morning at a magnitude of 4.3, while a second earthquake, of 3.2 magnitude, rumbled about 30 minutes later. Three additional earthquakes hit between 4:30 p.m. and 5:38 p.m. Saturday in the same area, registering magnitudes between 2.9 and 3.6, USGS reported. A 3.0-magnitude earthquake struck that night, at 11:37 p.m.
The geological activity continued into Sunday. USGS reported four earthquakes near Petrolia between 2:18 p.m. and 4:05 p.m. The earthquakes ranged in magnitude from 3.4 to 4.5.
More than 240 people, from Mendocino to McKinleyville, said they felt the 4.5-magnitude earthquake that struck Sunday at 2:18 p.m., according to the USGS’s online “Felt Report” page.
There was no initial word on damage or injury resulting from the quakes. The National Weather Service office in Eureka said Sunday afternoon there was no tsunami danger.
If you live in California, you’ll know the Big One is coming: a powerful earthquake of up to magnitude eight is headed for the state. Energy has been building up along the San Andreas Fault for more than a century. No-one knows exactly when or where, but that one day that energy will be unleashed.
It might strike at the heart of San Francisco, last devastated by a Big One in 1906. Or maybe it will tear through southern California like the magnitude 7.9 quake that hit in 1857 and ruptured some 225 miles of the San Andreas Fault.
More than 100 years on, it’s hard to predict exactly how hard the next Big One will hit. John Vidale, director of the Southern California Earthquake Center and affiliate professor at the University of Washington, told Newsweek it won’t look like in the movies—cities won’t collapse into rubble and tsunamis probably won’t sweep through California. But without adequate preparations, the Big One could “cripple” the finances of a state that just became the fifth largest economy in the world.
What exactly is a “Big One,” and where could such an earthquake hit?
A tectonic boundary between the North American and the Pacific plates cuts through California. It’s a big fault where the two sides are moving three or four centimeters a year sideways. Strain builds up for one or two hundred years along that boundary, and then finally that strain becomes so great that the fault can’t take it anymore. It breaks and moves 15 ft or so all at once, causing an earthquake.
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There’s three, four, five sections, to this fault—and many other faults running in parallel—but we worry about a Big One striking in the north or in the south of the San Andreas. There’s a part between north and south in central California that seems act like a buffer. There’s some chance a rupture could go end-to-end, but we think it’s either unlikely or that it just doesn’t happen.
How often do these massive earthquakes hit?
It’s every few hundred years. The earthquakes that have happened in the meantime are still devastating to a local area, but instead of magnitude eight, they’re more like magnitude seven. It’s a logarithmic scale, so an eight has about 30 times more energy than a magnitude seven.
Don’t smaller quakes help to dissipate some of the energy that’s building up deep underground?
Those little earthquakes let out only a tiny amount of energy compared to the big ones. It would take 10 magnitude seven earthquakes to let out the strain of a magnitude eight. We don’t have that many, so those little earthquakes hardly slow the big ones at all.
Does that mean the next big one is inevitable?
That’s right. When we look at the history of the fault, we can see these big earthquakes have happened many times over the last few thousand years, so yeah, it’s an inevitability. We just don’t know if it’s going to be now or two hundred years from now.
What kind of impact would a northern or southern California Big One have?