Drive about 100 miles east-northeast of San Diego and you’ll come to the Salton Sea, a quasi-oasis whose surface is so glassy it reflects the sky in exquisite detail.

Don’t be fooled by the serenity. You’re looking at a potential killer.

Beneath the seafloor lie strands of the southern San Andreas fault, a 340-mile system that could rupture all the way to Monterey County.

The result would be the “Big One,” an earthquake that experts said would collapse buildings, destroy freeways, warp rail lines and crack dams. Thousands of people could die.


No one knows when this will happen; scientists cannot predict quakes. And temblors don’t repeat on a neat schedule.

All we know for certain is that the fault has produced monster quakes in the past — and will do so in the future.

“The section of the fault from Parkfield to the Salton Sea is ripe for an earthquake,” said Tom Rockwell, a seismologist at San Diego State University. “Based on geodetic measures, about 15 feet of potential slip has accrued. Just think about what that will do to the (Interstate) 10 freeway, not to mention numerous other infrastructural elements. And then there is the shaking …”

Rockwell is describing a quake that could reach 8.0 in magnitude, which would be the second-largest ever recorded in California. But he isn’t trying to scare you.


He simply believes the public needs to be regularly reminded that it lives in earthquake country, a brittle nirvana that could be whacked by Mother Nature at any moment.

It’s a hard message to sell.

Big quakes are rare. San Diego hasn’t been jolted by one since April 2010, when a 7.2 temblor in northern Baja California ripped through Southern California.

“Everyone thinks about wildfires because they happen all the time,” said Neal Driscoll, a geoscientist at UC San Diego’s Scripps Institution of Oceanography. “That’s not true of quakes.”


They’re still worth talking about. As the late journalist Charles Kuralt said, “It takes an earthquake to remind us that we walk on the crust of an unfinished earth.”

Slowly but steadily, scientists are figuring out how this process works. And some of the findings are freaky and sobering.

Just ask Driscoll and Rockwell. They’ve been at the forefront of the research for decades.

As you might expect, they’ve spent a lot of time on the San Andreas, the dividing line between two of Earth’s great tectonic plates, the North American and the Pacific.


The southern tip of the fault passes through the Salton Sea, a shallow inland lake in the Colorado Desert. But the geology is more complicated than that. Driscoll published a paper last year that said a different fault crosses the San Andreas at the same spot, affecting the dynamics.

“We were able to show that when the Salton Sea floods, these cross-faults increase stress on the San Andreas,” Driscoll said. “That could trigger an earthquake.”

Such discoveries grab attention because much of the public believes the San Andreas is basically the only major seismic threat in Southern California.

That simply isn’t true.


Drive west from the Salton Sea and you’ll pass over the San Jacinto and Elsinore faults. Both systems are partly located in rural San Diego County. And both represent a clear and present danger.

Rockwell knows this from years of digging into the faults and reconstructing their history. In 2014, he announced that “A magnitude 7.5 was generally accepted to be the largest earthquake that would like occur on the San Jacinto. We have shown that the central and northern sections of the San Jacinto fault appear to fail together at times, and that would be in the magnitude 7.6 to 7.7 range.”

Such a quake would rattle skyscrapers in downtown San Diego.

More recently, Rockwell and doctoral student Drake Singleton discovered that San Diego’s Rose Canyon fault produces major earthquakes more frequently than scientists once believed. The trenching they did in Old Town showed that the fault appears to generate a 6.5 to 6.8 quake roughly every 700 years, rather than on a time-scale of 1,000 to 1,500 years.


The fault last produced a quake of that size about 300 years ago, so another major jolt doesn’t appear to be imminent. But the news is still worrisome because of the fault’s path — and because the scientific estimates keep changing as more discoveries are made.

The Rose Canyon fault extends from San Diego Bay through Old Town and across Mission Valley, then up Rose Canyon through Mt. Soledad and finally heading offshore at La Jolla, where it connects with the Newport-Inglewood fault.

“A powerful quake in the mid- to upper 6s could cause liquefaction around San Diego and Mission bays and locally in Mission Valley, and cause the land to be offset across the fault, which would damage buildings,” Rockwell said.

His announcement came in June, shortly after Driscoll and his collaborators revealed the clearest data yet that the Rose Canyon and Newport-Inglewood faults aren’t separate. They’re one system.


And that system is capable of producing a 7.3 quake that could damage the coasts of San Diego, Orange and Los Angeles counties.

Driscoll’s announcement struck many as logical. But people were a bit incredulous a year earlier when he and his colleagues disproved a 16-year-old hypothesis that said a large blind thrust fault existed off, and along, the coast of Oceanside.

“Science is about testing hypotheses,” Driscoll said. “Our tests showed that the fault doesn’t exist.”

Scientists now have a variety of tools to image fault systems in great detail, including those buried beneath the seafloor. And they can distribute data rapidly.


“As recently as 25 years ago, scientists struggled to determine locations, magnitudes and shaking maps for earthquakes like (the 6.7) Northridge (temblor) because seismic networks were blown out of the water, figuratively speaking, by big quakes,” said Susan Hough, a seismologist at the U.S. Geological Survey in Pasadena.

The bigger struggle may involve getting the public to prepare for the threats it already faces.

“It’s been a while since an earthquake of significant consequence has struck anywhere in California,” Hough said. “So people start to forget what a real earthquake can do. …

“If an earthquake struck at 2:30 a.m. and it was suddenly pitch dark, how many people would have a flashlight within reach of their beds? Or a pair of sturdy shoes within reach?


“How many people have automatic shut-off devices on their natural gas lines? Or have thought seriously about vulnerabilities of their homes?

“It isn’t an easy investment to make, retrofitting a chimney or cripple walls. Not every family can afford it.”

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gary.robbins@sduniontribune.com