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The coast has been shaken by seven earthquakes in less than a day, with four of them occurring in the same city near the San Andreas fault - prompting concerns that the "Big One" might be imminent.
The United States Geological Survey (USGS) reported a 3.7 magnitude earthquake at 4:59 pm ET in Hayward on Thursday.
Two hours prior, the USGS reported three new earthquakes in the areas surrounding Hayward and Petrolia, California.
A series of new earthquakes hit the affected areas within a 12-hour time frame, following a series of three earlier seismic events that occurred in the early hours of Thursday morning.
A 3.2 magnitude earthquake hit the city of Hayward at 2:52 pm ET, followed by a 3.2 magnitude earthquake two minutes later.
At 2:40 pm Eastern Time, a 2.9 magnitude earthquake was reported just off the California coast near Petrolia.
This seismic activity occurred just hours after the USGS recorded a 2.7 magnitude earthquake at 8:03 am ET on Thursday in the area near Hayward.
Two more earthquakes occurred within six hours of each other, approximately 250 miles north of the Hayward quakes, and slightly farther out to sea from Petrolia.
The United States Geological Survey reports that the initial earthquake struck at 2:06 a.m. ET, registering a magnitude of 3.3.
A second quake, measuring 3.4 on the magnitude scale, struck less than three hours after the initial one, at 4:51 am ET.
These earlier earthquakes near Petrolia occurred approximately 20 miles apart from each other in the vicinity of the coast.
The ones in Hayward are located in a region of the state that is situated between major cities like San Francisco, Oakland, and Fremont.
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The United States Geological Survey (USGS) reported that numerous individuals felt all three seismic events on Thursday morning, with over 100 residents experiencing shaking during the 2.7 magnitude quake.
The Hayward Fault extends along the base of the East Bay hills. The most recent significant earthquake occurred on October 21, 1868, with a magnitude of 6.8.
Historical documents indicate that five individuals lost their lives and thirty were wounded.
Researchers have been monitoring the fault, discovering that it generates significant earthquakes approximately every 140 years.
"Since it has been over 144 years since the last major earthquake, the clock is ticking," researchers at the University of California, Berkeley noted.
There is a high probability that the Hayward fault will experience a major earthquake in the next 30 years.
A significant fault in the Earth's crust that stretches approximately 1,300 kilometers in both depth and length across California.
The seismic events also took place adjacent to the Pacific plate - the oceanic tectonic plate that lies beneath the Pacific Ocean.
It is the largest tectonic plate on the planet, and recent studies have indicated that significant undersea fault lines may be causing it to break apart.
It has been discovered that the deep-sea faults beneath the ocean are caused by the immense forces within the Pacific plate pulling it to the west.
The San Andreas fault line is situated just a few miles away from the Hayward fault.
Seismologists have cautioned that a major earthquake along the San Andreas Fault in California is long overdue.
A magnitude 8 earthquake could cause extensive damage in California's heavily populated cities, resulting in approximately 1,800 fatalities, 50,000 injuries, and $200 billion in losses, as per the California Earthquake Authority's estimates.
Regarding the recent series of smaller earthquakes, seismic activity with a magnitude of 2.5 or higher is typically strong enough to be felt and may result in minor damage.
The San Andreas fault experienced another pair of earthquakes on February 10, causing tremors in San Bernardino.
The United States Geological Survey (USGS) detected a preliminary 3.5 magnitude earthquake at 12:44pm ET, followed by a 3.0 magnitude earthquake about four minutes later.
A 3.5-magnitude earthquake was felt in San Bernardino, as well as in Ontario, Victorville, Hesperia and Riverside.
Residents in Inglewood, Redondo Beach, Palm Springs, Huntington Beach and north San Diego County also reported feeling them, as one user said: 'Felt both!'
"I definitely felt that one today...just another day in California," wrote another.
According to the USGS Felt Report, over 230 individuals reported experiencing shaking.
Some people reported not feeling the quakes at all, as California is accustomed to more significant tremors.
'I'm currently in San Bernardino and I needed social media to let me know there was an earthquake,' a person said on X.
"No, I did not feel it. And I am in that area," another person said on Facebook.
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