The California coast has been rocked by seven earthquakes in less than a day, sparking fears that the 'Big One' could be on the way.

The United States Geological Survey (USGS) detected a 3.7 magnitude quake at 4:59 pm ET in the city of Hayward Thursday.

Just two hours earlier, three earthquakes hit near Hayward and Petrolia.

All four struck less than 12 hours after three seismic events rocked those same areas early morning.

A 3.4 magnitude earthquake was detected in the city of Hayward at 2:52 pm ET, followed by a 3.2 magnitude quake just two minutes later.

At 2:40 pm ET, a 2.9 magnitude earthquake was reported just off the coast near Petrolia and was preceded by a 2.7 magnitude quake at 8:03 am ET in nearly the exact same part of Hayward.

Two more earthquakes struck less than six hours earlier, roughly 250 miles north of the Hayward quakes.

The tremors near Petrolia hit on the San Andreas fault that scientists have been monitoring due to it being overdue for a major event that would cause significant damage and loss of life. 

USGS says the first tremor hit at 2:06 am ET, measuring a 3.3 magnitude.

It was quickly followed by another 3.4 magnitude quake less than three hours later at 4:51 am ET.

Those earlier earthquakes near Petrolia were centered roughly 20 miles apart from each other off the coast.

While the three quakes near Petrolia struck a relatively quiet part of northern California, the ones in Hayward are in an area of the state right in between major cities like San Francisco, Oakland, and Fremont.

The newest quakes in Hayward occurred right by the aptly named Hayward fault line, which USGS notes is an active fault in the San Francisco Bay region.

The USGS shows that hundreds of people reported feeling all three seismic events Thursday morning, with more than 100 residents reporting shaking during the 2.7 magnitude quake.

The Hayward Fault runs along the foot of the East Bay hills. The last major earthquake hit on October 21, 1868, measuring a 6.8 magnitude. 

Historical records show that five people were killed and 30 were injured. 

Scientists have been monitoring the fault, finding it produces major quakes ever 140 years. 

'Since it has been more than 144 years since the last major earthquake, the clock is ticking,' researchers at the University of California, Berkley stated.

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

The three magnitude-3 quakes near Petrolia took place near the northern portion of the infamous San Andreas fault, a major fracture in the Earth's crust that spans 800 miles up and down California.

The seismic events also occurred right along the border of the Pacific plate - the oceanic tectonic plate that lies beneath the Pacific Ocean.

It is the biggest tectonic plate on Earth, and recent studies have suggested that large undersea faults may be pulling it apart.

A 2024 study in Geophysical Research Letters found that the deep underwater faults are the result of enormous forces within the Pacific plate dragging it westward.

The San Andreas fault line also sits just miles away from the Hayward fault.

Experts have warned that California is overdue for another massive earthquake along the San Andreas.

A potential magnitude 8 quake would wreak havoc upon the state's most populated cities, causing roughly 1,800 deaths, 50,000 injuries, and $200 billion in damage, according to estimates by the California Earthquake Authority.

Experts are 'fairly confident that there could be a pretty large earthquake at some point in the next 30 years,' Angie Lux, project scientist for Earthquake Early Warning at the Berkeley Seismology Lab, told DailyMail.com in 2024.

As for this most recent series of smaller earthquakes, seismic activity above 2.5 in magnitude can often be felt and cause minor damage.

The San Andreas fault released another pair of earthquakes on February 10, rocking San Bernardino.

The USGS detected a preliminary 3.5 magnitude at 12:44pm ET, followed by a 3.0 magnitude about four minutes later. 

The 3.5 earthquake was felt in San Bernardino, as well as Ontario, Victorville, Hesperia and Riverside.

Residents in Inglewood, Redondo Beach, Palm Springs, Huntington Beach and north San Diego County reported feeling them as well, as one X user said: 'Felt both!'

'Yup felt that one...another day in California,' wrote another.

More than 230 people said they felt shaking, the USGS Felt Report said.

Others said they didn't feel the quakes at all, as California is used to larger tremors.

'Hell, I'm IN San Bernardino - and I needed social media to tell me there was an earthquake,' a person said on X.

'No, did not feel it. And I'm in that area,' another said on Facebook.