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How the Salton Sea may be delaying California's next giant earthquake

A MARTÍNEZ, HOST:

The Salton Sea in Southern California is not a sea. It's the state's largest lake. And it might be delaying the region's next giant earthquake. That's right, possibly delaying the big one. That's according to a study just out in the journal Nature. The Lake may be helping to keep stress off the southern portion of the San Andreas Fault, one of the world's largest faults. Joining us now for more on the study is reporter Erik Anderson with member station KPBS in San Diego. So Erik, let's start by giving us a sense of where the Salton Sea is, how it came to be and why it's so important to seismologists.

ERIK ANDERSON, BYLINE: Yeah, it's located just north of Mexico, about 130 miles east of San Diego. The current lake was created by agricultural runoff after a berm broke back in 1905. Now, the Earth's crust is pretty thin here, which allows for plenty of geothermal energy - that's underground heat that can be tapped - and lots of small earthquakes. There have been just under a thousand measurable earthquakes in the past month, most of them, of course, too small to feel.

MARTÍNEZ: And I'm guessing the San Andreas Fault has a lot to do with that.

ANDERSON: Yeah, it's at the southern end of that 800-mile-long San Andreas Fault. Now, the fault line, you might know, is famous for generating the damaging San Francisco earthquake back in 1906 and the Loma Prieta quake in 1989. Scientists fear that the next big rupture generated here at the southern end could be strong enough to send multiple damaging shockwaves through the Los Angeles Basin. That's a region where more than 14 million people live.

MARTÍNEZ: And the study out in the journal Nature shows a connection between the size of the lake and its impacts on seismic activity. Tell us about that.

ANDERSON: Yeah, the study's author, Ryley Hill, says that geological research allowed them to build a computer model that links the strong ruptures over time to times when the valley was filled with water. The Colorado River has filled this valley about six times over the past thousand years. And at times, the lake has held up to 30 times more water than the current sea does. Now, the weight of that water pushes down on the Earth's crust. And it lubricates the faults, boosting chances for a big quake. And Hill says, now that the Salton Sea is shrinking because of drought and less agricultural runoff, that means there is less pressure on the volatile southern tail of this earthquake fault system.

RYLEY HILL: It's a section that is currently locked. And it's been locked for 300 years, OK? Now, the last major rupture was in 1725. And over the past 1,000 years, we've actually had probably six or seven large events.

ANDERSON: Scientists are puzzled why there hasn't been a major earthquake here in the last 300 years. Historical records show that one should have happened every 180 years or so. A smaller lake does help ease pressure on the fault.

MARTÍNEZ: The thing is, though, Erik, I mean, this is Southern California we're talking about here. This is an area that's primed for a quake. A lot of pent-up energy there - that's got to worry seismologists.

ANDERSON: Yeah, Hill and others say that the longer the region goes without a major event, more seismic stress does build up. And that increases the chances that the next big earthquake on the southern San Andreas fault could be the big one. But scientists also caution that the size of the lake in the Salton trough is only one factor that influences seismic activity. There are many others.

MARTÍNEZ: That's reporter Erik Anderson with KPBS in San Diego. Erik, thanks a lot.

ANDERSON: My pleasure.

(SOUNDBITE OF KINACK SONG, "SHINE") Transcript provided by NPR, Copyright NPR.

Erik Anderson