Scientists have detected a cluster of 11 recent earthquakes off the west coast, five of which struck in just the last 24 hours.
The quakes shook the sea 126 miles (203 km) off the coast of Crescent City, California.
The tremors, which ranged in magnitude from 2.8 to 5.6 on the Richter scale, occurred some six miles (10km) underwater on the seabed at the Juan de Fuca tectonic plate.
This area forms part of the Cascadia Subduction Zone, which runs from Northern California to the Canadian region of British Columbia, and is considered just as infamous as the San Andreas fault by experts.
Previous studies have warned the Cascadia zone has the potential to deliver an earthquake even stronger than the one predicted to devastate the area above the San Andreas’ one.
A full rupture along the 650-mile-long (1,000 km) offshore fault could trigger a 9.0 magnitude earthquake which would be followed by a horrifying tsunami, according to seismologists.
The ‘Big One’, a huge earthquake expected to occur in the future along the San Andreas Fault, could be of magnitude 8 or greater.
The Juan de Fuca tectonic plate is considered dangerous because it is under constant strain from the neighbouring Pacific plate, which for the last 300 years has been pushing it beneath it, creating the Cascadia Subduction Zone.
Scientists expect the Juan de Fuca will eventually be pushed underneath the North America plate, where Canada and the US sit, causing the region to sink at least six feet.
This movement could trigger one of the biggest earthquakes ever recorded in history, seismologists said.
Chris Goldfinger, a professor of geophysics at Oregon State University told CNN: “Cascadia can make an earthquake almost 30 times more energetic than the San Andreas to start with.
“Then it generates a tsunami at the same time, which the side-by-side motion of the San Andreas can’t do.”
Despite sparking fears, the latest cluster striking the area didn’t bring the United States Geological Survey (USGS) to issue a warning, as the institute doesn’t believe they pose a risk of tsunami.
Don Blakeman, a geophysicist at the National Earthquake Information Center, said quakes of this calibre are not serious, and occur fairly often off the coast.
The largest of the earthquakes occurred at 7.44am local time (3.44pm BST) on 24 July.
Earthquakes of similar magnitudes on the Richter scale are categorised as “causing damage of varying severity to poorly constructed buildings”.