The city of Los Angeles alone has more than 13,000 soft-story buildings — structures built over open parking areas, which are at risk of pancaking during an earthquake. There are also more than 1,000 non-ductile concrete buildings — the same kind experts say collapsed after the recent earthquakes in Turkey and Syria. 

Millions of Southern Californians live in areas without retrofit mandates. The city of L.A. has one, but the deadline is still decades away. 

Structural engineer Kit Miyamoto — who saw the devastation firsthand in Turkey and compared it to the aftermath of the Hiroshima nuclear blast —  said he feels like Southern California is on borrowed time. 

"That's 100% guarantee," he said. "I mean, there would be a gigantic earthquake happening in Southern California." 

The San Andreas fault is capable of producing a magnitude-7.8 earthquake near Los Angeles, which could send waves of intense shaking through the Los Angeles basin for several minutes, said Monica Kohler, earthquake engineer at CalTech.

In 1994, the magnitude-6.7 Northridge earthquake struck L.A., killing 57 people and injuring thousands. 

"I am afraid that because the last large earthquake happened long enough ago, we've forgotten about it," Kohler said. "We need to bring that to the forefront." 

Kyle Tourjé, senior structural assessor with Alpha Structural, said his crews are staying busy retrofitting buildings.

"It's expensive to do these retrofits," Tourjé said. "But if you don't have a building left, that's more expensive. If you have tenants that you've lost, that's the biggest loss you can have."