CALIFORNIA could be at risk of a small-scale tsunami due to two fault lines off the state’s coast that could shake Los Angeles, a new study says.
The new information published in the Journal of Geophysical Research: Earth Surface follows the release of disaster film “San Andreas,” which depicts a catastrophic earthquake, resulting in a tsunami that destroys San Francisco’s Golden Gate Bridge.
Mark Legg, the study’s lead author, said a real-life offshore earthquake and tsunami would not mirror what happened in the movie, although the hazard deserves more attention than it has received.
“That has not been looked at carefully when it comes to the potential for large earthquakes and tsunamis from offshore faults,” Legg, who runs a Southern California consulting firm called Legg Geophysical, told NBC News.
The two other faults that could prompt a tsunami – the Santa Cruz-Catalina Ridge Fault and Ferrelo Fault – are underwater and building up stress similarly to the San Andreas Fault, and could potentially generate an 8.0 magnitude earthquake.
“We’re dealing with continental collision,” Legg said in a press release. “That’s fundamental. That’s why we have this mess of a complicated logjam.”
Other earthquake experts, however, say the hazard has been examined, although they acknowledge that offshore faults deserve further study.
“It’s a complicated picture, and this is an important piece of it,” said Lucy Jones, science adviser for risk reduction in the U.S. Geological Survey’s Natural Hazards Mission Area, according to NBC News.
Research used mapping data from a 2010 depth survey that spanned more than 2,800 miles of fault lines on the ocean floor, and data from previous surveys. From measurements, researchers concluded that the seafloor crust in the regions was subject to strike-slip forces and vertical compression.
“What they were searching for are signs, like those seen along the San Andreas, that indicate how much the faults have slipped over time and whether some of that slippage caused some of the seafloor to thrust upwards,” the American Geophysical Union, which publishes the journal, said in a press release.
In an Los Angeles Times article, Thomas Jordan, director of the Southern California Earthquake Center and a professor at University of Southern California, explained that the San Andreas Fault would not be able to create a tsunami that would inundate San Francisco, as the fault is mostly on land; big tsunamis are created by faults underwater.
Thomas added that the fault is vertical, so even when it goes underwater, “it doesn’t move the ocean floor up or down very much.”
Legg’s research focused on “transpression” faults, which follow more of a side-to-side movement. Jones said these wouldn’t produce such devastating consequences as the tsunamis that hit Sumatra in 2004 and Japan in 2011; both of these instances occurred in subduction zones, where one tectonic plate slips under another.
“It’s not that it’s not a risk,” Jones said. “It’s just not as big a risk as the ones we see from the big subduction zones.”
The subduction zone closest to Southern California is the Cascadia Subduction Zone, which is found off the coast of Northern California, Oregon and Washington.
Legg said the there are two big takeaways from the research. The first is not to panic and be prepared.
“Worrying doesn’t do any good. Preparedness is key,” he said.
For instance, if one is at the beach and sees the ocean receding dramatically, one should run to higher ground, as a large tsunami wave is probably on its way.
Secondly, Legg called for a closer study of undersea faults.
“We’ve got high-resolution maps of the surface of Mars,” he said in a statement. “Yet we still don’t have decent bathymetry for our own backyard.” (Agnes Constante/AJPress with reports from Los Angeles Times, International Business Times, NBC News and TIME)
