While most people are obsessed with the disaster portrayed in the big-budget movie San Andreas, a group of researchers have found that there looms a real tsunami threat offshore Southern California. Just 90 miles off the coast, there are several major faults with the potential of producing massive earthquakes, sending tsunami waves crashing into Los Angeles and San Diego.
Active offshore faults can produce magnitude 8 quakes
According to a study published in the Journal of Geophysical Research: Earth Surface, these active faults offshore Southern California can produce greater than magnitude 8.0 quakes. Geologist Mark Legg, the lead author of the study, said that there is no need to panic, but we should be prepared because now we know there is a real tsunami potential in California.
There is evidence that the last major tsunami hit Southern California in 1812. However, Legg said geologists don’t have the necessary data to predict when the next one could occur. They are working on a detailed seismic forecast. A project to map the Pacific seafloor within 200 miles of the coast was shelved in 1990s due to federal budget cuts. It hasn’t been revived yet.
Don’t ignore offshore faults that could trigger massive tsunami waves
Legg said people mostly focus on the onshore faults such as San Andreas that go through cities and have the potential to produce massive earthquakes, but we cannot ignore offshore faults. To conduct the study, Legg and his colleagues used mapping data from a depth survey in 2010 that covered approximately 2,800 miles of fault lines on the ocean floor.
The survey showed a “complicated logjam” of faults resulting from the smash-up of the North American tectonic plate and the Pacific plate. They focused on two fault zones in the Borderland: the Ferrelo Fault and the Santa-Cruz-Catalina Ridge. The seafloor crust in these areas is subject to vertical compression as well as horizontal strike-slip forces. Computer simulations showed that these offshore faults could produce magnitude 8 earthquakes.
Researchers found evidence that the Santa Cruz-Catalina Ridge Fault was slipping sideways, just like the plates along the San Andreas fault line.