LOS ANGELES (CBSLA.com) — The San Andreas fault may be the villain in Hollywood’s latest blockbuster disaster movie, but geologists say offshore faults pose a bigger threat to California, according to a new study.

Vertical fault zones in the undersea landscape off Southern California and northern Baja California have the potential for a magnitude 7.9 to 8.0 earthquake and a destructive tsunami wave aimed right at the cities of Los Angeles and San Diego, according to a study published recently in the Journal of Geophysical Research: Earth Surface.

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New seafloor depth measurements of the area called the California Continental Borderland, which includes the Channel Islands, show the structures of the Santa Cruz-Catalina Ridge fault and the Ferrelo fault to look alarmingly similar to the San Andreas fault, geologist and co-author of the study Mark Legg said.

“We can have a very large earthquake, maybe up to magnitude 8, like the San Andreas, but maybe not as frequent. The San Andreas fault is moving fastest in California, so it has the large earthquakes most often,” Legg said.

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But unlike the San Andreas, these seafloor faults are moving vertically as well as sideways, which makes tsunami activity for large cities like Los Angeles and San Diego a very real concern.

“We can’t predict earthquakes, so we can’t predict a tsunami,” said Monica Kohler, a Legg’s co-author and an assistant research professor at Caltech’s Department of Mechanical and Civil Engineering.

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“Tsunami risk, even not a large tsunami, should still be something we worry and prepare for, because these faults are so close to the shore and the [Channel] Islands,” Kohler said.