Earlier this month, scientists announced the discovery of a new fault line in Southern California that runs parallel to the San Andreas Fault. Now, geologists have found a direct link between two fault lines underneath the waters of the San Francisco Bay.

The connection places the area and the people who live there at risk of a big earthquake in the near future.

In a new study published in the journal Science Advances, scientists from the U.S. Geological Survey used a specially designed seismic profiler to build a new map that can show where the Hayward Fault and the Rodgers Creek Fault connect, which allowed them to find a clear link between the faults.

"Detailed subsurface imaging provides definitive evidence of active faulting along the Hayward fault as it traverses San Pablo Bay and bends ~10° to the right toward the Rodgers Creek fault," the researchers wrote in their study. "Integrated geophysical interpretation and kinematic modeling show that the Hayward and Rodgers Creek faults are directly connected at the surface."

Knowing how these faults are connected allows scientists to more accurately estimate how these faults may rupture together in the future, which could potentially set off a large earthquake.

Study researcher and USGS geophysicist Janet Watt explained that the size of earthquakes that can possibly occur on a fault will depend on the length of the fault. Two faults that are interlinked instead of being separate fault segments make a longer fault and this raises the possibility of a larger earthquake.

In the new study, Watt and colleagues estimated that if the two faults would rupture together along their entire length that spans 118 miles, the event could possibly generate up to a magnitude 7.4 earthquake.

If such quake would happen, it would be California's fifth largest earthquake. Study researcher David Ponce from the USGS said that this quake could happen soon, with a 32 percent likelihood it could occur anytime in the next 30 years.

Given the population in the affected area, an earthquake this strong is likely to be very deadly. More than 2.4 million people currently live right along the fault and the whole area is populated by around 7.5 million people. Gas, water, major transportation and electrical lines also cross this fault, which means that a big earthquake would be very disastrous.

A 7.4 magnitude earthquake would release energy fivefold of that released by the 6.9 magnitude Loma Prieta earthquake that struck California in 1989, which killed 63 people and caused damage estimated between $6 billion and $10 billion.