An earthquake has struck California's Bay Area right along a fault line experts now fear may be the surprise cause of the long-awaited 'Big One.'

The US Geological Survey (USGS) said the 3.2 magnitude quake struck in the city of Concord at 3:11pm ET Friday afternoon.

Concord, home to more than 120,000 Californians, is just 25 miles from San Francisco. There have been no reports of any injuries, according to KGO.

This is the fourth minor earthquake to strike the city in the last 24 hours. However, the other three were weaker than Friday' 3.2 magnitude tremor. 

Concord sits just five miles from the Hayward Fault, a 74-mile fault line that runs along the foot of the East Bay hills.

While Friday's earthquake likely wasn't felt in San Francisco, experts fear the Hayward Fault could soon unleash a historical earthquake that devastates the entire Bay Area.

Although the 800-mile San Andreas Fault has been the focal point of most seismic studies in California, researchers fear the Hayward Fault is now overdue in delivering an earthquake greater than 7.0 in magnitude in the next few years.

A USGS simulation, called the HayWired Scenario, projected that a magnitude 7.0 quake on the Hayward Fault could result in between 800 and 2,500 deaths throughout major Bay Area cities like San Francisco and Oakland.

The last major earthquake along the Hayward hit on October 21, 1868, measuring 6.8 in magnitude.

Scientists at the University of California, Berkley have found that the fault line produces a major earthquake every 140 years. 

'Since it has been more than 144 years since the last major earthquake, the clock is ticking,' the researchers warned.

'It is very likely that the Hayward fault will rupture and produce a significant earthquake within the next 30 years.'

USGS has made an even more ominous prediction, warning that a massive seismic event could strike the Bay Area by 2032, just seven years from now.