A swarm of over 30 earthquakes hit Southern California near the Salton Sea, raising fears of the long-anticipated “Big One.” The strongest quake struck at 4.3 magnitude early Friday, followed by dozens of smaller tremors. “Several dozen small and moderate-sized earthquakes struck the area,” the USGS confirmed.

The swarm occurred near the San Andreas and Elsinore fault lines—both capable of triggering powerful earthquakes. The 4.3-magnitude quake hit just 40 miles from San Andreas and about 50 miles from Elsinore, a fault seismologist Lucy Jones warned “is still capable of producing an earthquake up to 7.8 in magnitude.”

No injuries or major damage have been reported, though people as far as 100 miles away felt the shaking. Many residents noted feeling the larger quake but missed the smaller ones.

Experts warn these swarms could precede a megaquake. A 7.8-magnitude simulation by USGS projected “violent shaking and widespread structural damage” in Los Angeles, with destruction levels reaching 7.5 to 9.0 on the Modified Mercalli Intensity scale. San Diego could also face cracked walls, collapsed chimneys, and structural damage.

While no immediate disaster has occurred, scientists continue monitoring the situation closely.