The Southern San Andreas fault has not generated a major earthquake in 300 years, and San Diego researchers think a shrinking Salton Sea may partly be responsible.
A new paper published in the current edition of the scientific journal Nature suggests that the ebb and flow of water in the desert region may be linked to seismic activity there.
The Salton Sea was created in 1905 when an irrigation berm broke and flooded a part of Imperial County with Colorado River water. The valley sits below sea-level about 130 miles east of San Diego. California’s largest lake has been shrinking ever since.
That contraction is happening more rapidly in recent years because of drought and less agricultural runoff.
The filling and emptying of that desert floor has happened regularly over the past 1,000 years and the dry and wet cycles are affecting the region’s unstable geology.
San Diego State University researchers pointed to the geological record, which shows that a large lake has formed there at least six times over the past 10 centuries.
One incident created Lake Cahuilla, a body of water that held 32 times the amount of water in the current Salton Sea.
Researchers found the water is heavy enough on its own to create seismic activity.
The huge lake bent the earths’ crust — which is especially thin in this region — and forced water into crevices underground. That essentially lubricated the fault, making it easier for major ruptures to occur.
“When the lake was really high, stress changes on the lake were high enough both to promote an earthquake, but also potentially change the timing of that earthquake, either accelerate or decelerate it,” said Matt Weingarten, a San Diego State University researcher who co-authored the paper.
There are more than 5,000 earthquakes measured in the area every year, although most are too small to feel.
The North American and Pacific tectonic plates are rubbing against each other along the 800-mile long San Andreas Fault. The north portion of the fault is responsible for the damaging San Francisco earthquake in 1906 and the Loma Prieta quake in 1989. The southern tail runs beside the Salton Sea before it ends under the desert valley.
And the earth’s crust is also thin there, making Imperial County a prime spot to harvest geothermal energy.
The region is also overdue for a major seismic event.
“It’s a section that is currently locked,” said Ryley Hill, the study’s lead author and a graduate student at San Diego State University and the Scripps Institution of Oceanography. “And it’s been locked for 300 years. The last major rupture was in 1725. And over the past 1,000 years we’ve had probably six or seven large events .”
A major rupture typically happens every 180 years.
Scientists do not know why there has been such a long earthquake drought, but a smaller lake could extend that run.
However, they also worry that pressure building along the fault might mean the next major rupture could be massive.
“This implies that the tectonic stress has accumulated in that time period,” Hill said. “Which, instead of relieving that stress in a sequence of events that was shorter in time. You’re building up a lot of stress.”
The next major temblor to erupt in the region has the potential to be “The Big One.”
A strong earthquake centered in this valley would likely reverberate up into the Los Angeles basin with the potential to create billions of dollars in property damage while putting lives at risk.
