Continental Crash May Trigger California Earthquake and Tsunami

California may be in danger of facing a tsunami. Researchers have discovered several major faults that lie offshore and could cause quakes and tsunamis that may impact the west coast.

"We're dealing with continental collision," said Mark Legg, one of the researchers, in a news release. "That's fundamental. That's why we have this mess of a complicated logjam."

In this case, the researchers examined blocks of the Earth's crust that are caught in the ongoing tectonic battle between the North American tectonic plate and the Pacific plate. The blocks are wedged together all the way from the San Andreas Fault on the east, to the edge of the continental shelf on the west, from 90 to 125 miles offshore. These chunks of crust get squeezed and rotated as the Pacific plate slides northwest, away from California, relative to the North American plate. The mostly underwater part of this region is called the California Continental Borderland, and includes the Channel Islands.

The researchers combined older seafloor data and digital seismic data from earthquakes along with 2,756 miles of new seafloor depth measurements collected in 2010. This revealed the structure of two of the larger seafloor faults in the Santa Cruz-Catalina Ridge Fault and the Ferrelo Fault.

In the end, the researchers found ridges, valleys and other clear signs that the fragmented, blocky crust has been lifted upward, while also slipping sideways like the plates along the San Andreas Fault do. The Ferrelo Fault zone actually showed thrust faulting, which is an upwards movement of one side of the fault. The vertical movement means that blocks of crust are being compressed as well as sliding horizontally relative to each other.

As Southern California's pile-up continues, the plate movements that build up seismic stress on the San Andreas are also putting stress on the long Santa Cruz-Catalina Ridge and Ferrelo Faults. Like the Sand Andreas, these faults may rupture in the same way.

"Such large faults could even have the potential of a magnitude 8 quake," said Christopher Sorlien of the University of California who wasn't involved in the study. "This continental shelf off California is not like other continental shelves-like in the Eastern U.S."

The findings are published in the Journal of Geophysical Research: Earth Surface.

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