Researchers have discovered that ancient rising lakes may trigger California earthquakes along the San Andreas fault line.
Collecting field data from rocks near the fault, Hill and his colleagues found earthquakes occurred about every 180 years, give or take 40 years, and coincided with the high water levels of the nearby ancient Lake Cahuilla.
The San Andreas Fault is the border section between two massive tectonic plates under the surface of the Earth and stretches for more than 800 miles through California, past San Francisco down to San Diego.
The southern end of the fault lies next to what is now known as the Salton Sea, a remnant of the ancient lake. Lake Cahuilla used to fill periodically over the past thousand years but is now causing a seismic drought, going more than 300 years without a major earthquake.
The San Andreas Fault has been causing concern among experts as multiple segments appear to be significantly stressed. For this reason, they fear that a gigantic earthquake could be imminent.
“This fault poses the largest seismic hazard in all of California,” Hill explains. “The southern San Andreas fault is a locked section, and when this fault ruptures … it would cause significant damage to the Los Angeles metropolitan area.”
According to this new study, this earthquake could have been triggered by a rapid filling of the Salton Sea.
“This section of the San Andreas Fault has accumulated much tectonic stress. While it is doubtful that Lake Cahuilla will fill again, there is potential that the Salton Sea, the modern-day remnant of Lake Cahuilla, may be filled again,” Hill said. “There is evidence to suggest that it might not just be the total weight/size of the lake that can trigger an event but the rate at which the lake fills. So if we were to rapidly increase the Salton Sea filling, I would be apprehensive about potentially triggered earthquakes on the [southern fault].”
The U.S. Geological Survey has previously predicted that it is very likely that some areas across the San Andreas Fault will experience a magnitude 6.7 earthquake in the next 30 years.
Hill says the positives are that the odds of the Salton Sea refilling back to the size of ancient Lake Cahuilla “is impossible, thankfully.” But warns that he and his colleagues found that it’s not necessarily the volume that could add stress but the rate at which the lake could be filled.
Lake Cahuilla was about 32 times as big as the present-day Salton Sea and fed from the Colorado River. Hill adds that the Colorado River cannot deliver as much water to the Salton Sea because of drought and overallocation.
This is problematic because of plans to restore the Salton Sea, which has increasingly been affected by climate change and an area of toxic dust.