The San Andreas fault in Southern California is “locked, loaded and ready to go,” a leading earthquake expert has warned at the National Earthquake Conference last week.

The San Andreas is the longest fault and among the riskiest in the state. Southern California, however, suffered the last big earthquake from the southern part of the fault in 1857, in which a magnitude 7.9 quake ruptured 185 miles from Monterey County and the San Gabriel Mountains, neighboring Los Angeles.

“The springs on the San Andreas system have been wound very, very tight,” said Thomas Jordan, Southern California Earthquake Data Center director.

It’s not just that part of the fault that is far overdue. Others that have not moved include those in San Bernandino County since an 1812 quake, and further southeast leading to the Salton Sea since around 1680 to 1690.

Based on tectonic plate movement observed by scientists, earthquakes must be relieving around 16 feet of cumulative plate movement every century. The San Andreas fault has not performed that stress-relieving act for more than 100 years now.

According to the Southern California Earthquake Data Center, if the 1857 shock happens today, it could bring about massive damages worth billions of dollars.

“[T]he loss of life would likely be substantial, as the present day communities of Wrightwood, Palmdale, Frazier Park, and Taft (among others) all lie upon or near the 1857 rupture area,”wrote the center.

Jordan urged the state to focus on resilience programs and prepare for a quake as strong as magnitude 8. He lauded the political will in L.A. to require quake retrofits on buildings as pushed by Mayor Eric Garcetti, but eyed other areas of focus such as fortifying the city’s telecommunications networks and aqueduct systems.

L.A. is not located directly along the fault line, yet could suffer the impact of a major quake, such as “large shaking” continuing for long time periods, warned Jordan. The center arrived at the possibility in 2010 when it simulated magnitude 8 earthquake using the largest supercomputer in the world at the time.

In 2008, a report from the U.S. Geological Survey (USGS) predicted that a magnitude 7.8 quake on the southern section of the fault would result in more than 1,800 deaths, 50,000 injuries and $200 billion worth of damages and long-term disruptions.