Yesterday morning a series of 10 earthquakes struck Monterey County, California along the San Andreas fault line and has Cali residents increasingly concerned that the "Big One" could be next. The quakes, the biggest of which measured 4.6 on the Richter scale, hit near Salinas, California but were felt 90 miles away in San Francisco. Per SF Gate:
A 4.6-magnitude earthquake rattled Monterey County on Monday and was felt more than 90 miles away in San Francisco, officials said.
The quake hit at 11:31 a.m. about 13 miles northeast of Gonzales, near Salinas, and was followed by nine smaller aftershocks, with the largest measuring magnitude 2.8, said Annemarie Baltay, a seismologist with the U.S. Geological Survey in Menlo Park.
There were no reports of injuries or damage.
Baltay said the quake occurred on the San Andreas Fault, close to an area where the Calaveras Fault branches off. The quake happened at a depth of about 4 miles.
While a seismologist for the US Geological Survey, Annemarie Baltay, dismissed the recent quakes as part of 'normal seismic activity', the Director of the Southern California Earthquake Center offered a slightly different opinion to the LA Times last year:
“Any time there is significant seismic activity in the vicinity of the San Andreas fault, we seismologists get nervous,” said Thomas H. Jordan, director of the Southern California Earthquake Center, “because we recognize that the probability of having a large earthquake goes up.”
As seismic activity drops, the probability of having a large earthquake also decreases.
Experts said it’s important to understand that the chance of the swarm triggering a big one, while small, was real.
“When there’s significant seismicity in this area of the fault, we kind of wonder if it is somehow going to go active,” said Caltech seismologist Egill Hauksson. “So maybe one of those small earthquakes that’s happening in the neighborhood of the fault is going to trigger it, and set off the big event.”
Of course, Thomas Jordan is the same California Seismologist who raised some eyebrows last year when he proclaimed that the San Andreas fault is well overdue for a major quake.
“The springs on the San Andreas system have been wound very, very tight. And the southern San Andreas fault, in particular, looks like it’s locked, loaded and ready to go,” Jordan said in the opening keynote talk.
Other sections of the San Andreas fault also are far overdue for a big quake. Further southeast of the Cajon Pass, such as in San Bernardino County, the fault has not moved substantially since an earthquake in 1812, and further southeast toward the Salton Sea, it has been relatively quiet since about 1680 to 1690.
Here’s the problem: Scientists have observed that based on the movement of tectonic plates, with the Pacific plate moving northwest of the North American plate, earthquakes should be relieving about 16 feet of accumulated plate movement every 100 years. Yet the San Andreas has not relieved stress that has been building up for more than a century.
Jordan went on to say that when the tension that has been building along the San Andreas fault is finally relieved, it could potentially produce a magnitude 8 earthquake. Here's what a Magnitude 8 quake would look like...