A concerning new study identified significant earthquake and tsunami risks associated with seven major faults off the coast of Southern California.
The recent study suggests these vertical fault zones have displaced the sea floor, upping the risk of 7.9 to 8.0 earthquakes and tsunami waves that could damage cities such as Los Angeles and San Diego, the American Geophysical Union reported.
"We're dealing with continental collision," said geologist Mark Legg of Legg Geophysical in Huntington Beach, Calif., in reference to the cause of the offshore danger. "That's fundamental. That's why we have this mess of a complicated logjam."
The "logjam" is created by blocks of the Earth's crust involved in a "tectonic battle" between the North American tectonic plate and the Pacific plate. The blocks get moved around and squeezed together as the Pacific plate slides away from California.
The researchers combined seafloor and digital seismic data to determine how much the faults have slipped over time whether it was causing the seafloor to pucker upwards. The data confirmed both upward and sideways movement of the seafloor along the Santa Cruz-Catalina Ridge Fault. Regions around the Ferrelo Fault zone showed signs of thrust faulting, which is an upward movement on one side of the fault. This suggests the blocks of crust are being compressed and sliding horizontally in what was described as "transpression." The plate movement is believed to be building up seismic stress on the San Andreas, Santa Cruz-Catalina Ridge, and Ferrelo Faults.
"Such large faults could even have the potential of a magnitude 8 quake," said geologist Christopher Sorlien of the University of California at Santa Barbara, who is not a co-author on the new paper. "This continental shelf off California is not like other continental shelves - like in the Eastern U.S."
The findings were published in a recent edition of the Journal of Geophysical Research: Earth Surface.