The US state sits on top of the potentially catastrophic fault, a chasm between two massive plates of the Earth’s crust that extends hundreds of miles across the country.
Recently, there have been signs the fault is building pressure beneath the surface and could rupture.
In the last week, a three mile stretch of the San Andreas Fault around Monterey County, just south of San Jose, has been hit by 134 earthquakes, with the largest registering at 4.6 on the Richter scale – strong enough to be felt 90 miles away in San Francisco – at 11.31 AM local time on Last Monday.
Of the rest, 17 were of a magnitude 2.5 or higher, and six above 3.0.
Now experts warn there could be more to come.
Ole Kaven, a US Geological Survey (USGS) seismologist, said: “This one has been a quite productive aftershock sequence.
“We suspect there will be aftershocks in the two to three [magnitude] range for at least a few more weeks.”
The fear remains a huge quake could strike and researchers warn that a small flurry of tremors could be a sign that a larger one is warming up – but experts can not be sure, leaving locals to hope for the best.
John Bellini, a geophysicist at the US Geological Survey (USGS), recently said: “We can’t predict or forecast earthquakes.
“Sometimes before a large earthquake you’ll have a foreshock or two, but we don’t know they’re foreshocks until the big one happens.”
Also, beneath California, the Pacific and North American tectonic plates are moving northward – although the former is moving quicker leading to a build up of tension.
A powerful earthquake in 1857 released some of this pressure, but much more still exists, and Robert Graves, a research geophysicist at USGS, suggests the Big One could be overdue by 10 years.
He told Raw Story: “The San Andreas fault in southern California last had a major quake in 1857 (magnitude 7.9).
“Studies that have dated previous major offsets along the fault trace show that there have been about 10 major quakes over the past 1,000-2,000 years… the average time between these quakes is about 100-150 years.”