Californians have been keeping an eye on the San Andreas Fault for years fearing a “big one” would strike and cause massive damage.

Now, scientists say that a quake of 7.5 or bigger on a lesser known fault might be even more catastrophic than a quake along the San Andreas Fault line.

The Puente Hills thrust fault, which was the fault which brought Friday night’s 5.1 magnitude quake, runs from northern Orange County through downtown Los Angeles and all the way into Hollywood.  The San Andreas Fault runs along the outskirts of Southern California’s metro areas.

Thus, scientists say, a massive quake along the Puente Hills fault would cause significantly more damage and likely brings hundreds or thousands of deaths.  One estimate from the U.S. Geological Survey estimated as many as 1,800 deaths and $250 billion in damage.

The same fault in 1987 had a 5.9 quake that killed eight people and caused $350 million in damage.

One USGS staffer said that a 7.5 quake centered in Los Angeles would be so intense that it would throw heavy objects like a grand piano into the air.