The latest disaster flick, San Andreas, pulled in an estimated $53.2 million this weekend.

Hollywood loves to take disaster movies to the extreme, but Southern California faces real dangers from tsunamis.

The San Andreas fault is the most well-known in California. But, new research highlights lesser known faults just offshore of Southern California.

“We’re dealing with continental collision,” said geologist Mark Legg. “That’s fundamental. That’s why we have this mess of a complicated logjam.”

This ‘logjam’ consists of several tectonic blocks and faults that have the potential to produce earthquakes up to magnitude 8, according to Legg.

The map below shows the various blocks and faults just offshore.

faults off southern california

Credit: Mark Legg

These blocks and faults are pushed and pulled as the Pacific plate slowly slides northwest.

Legg and his colleagues were interested in two particular faults. The Santa Cruz-Catalina Ridge Fault and the Ferrelo Fault. During their study, the researchers combined older seafloor data with 4,500 kilometers of new seafloor depth measurements (also called bathymetry) collected in 2010. They also looked at digital seismic data from earthquakes.

The data shows Kegg and his researchers how much the faults have slipped over time and if this slippage caused some of the seafloor to thrust upwards.

The researchers found clear evidence of upward movement along the Santa Cruz-Catalina Ridge fault. Ridges and valleys showed the crust lifted upward and also slipped sideways. The Ferrelo Fault showed upwards movement on one side of the fault, known as thrust faulting.

Legg calls this sideways and upward movement “transpression.”

We know California is at risk of tsunamis, but how bad would it be? Ask anyone about tsunamis and they will instantly think about the one that hit areas in the Indian Ocean in 2004. Or, the massive tsunami that smashed into Japan in 2011.

Tsunamis from these two faults would be more local and not as devastating as those. But, any tsunami is dangerous.

“Because of their potential for dip-slip rupture, the faults may also be capable of generating local tsunamis that would impact Southern California coastlines, including populated regions in the Channel Islands,” the researchers write in the study abstract.

One problem the researchers highlight is the lack of information about the continental shelf right off California. It’s one of the least mapped and understood according to Christopher Sorlien, a geologist at the University of California at Santa Barbara.

“This is one of the only parts of the continental shelf of the 48 contiguous states that didn’t have complete … high-resolution bathymetry years ago,” Sorlien said

Legg added, “we’ve got high-resolution maps of the surface of Mars, yet we still don’t have decent bathymetry for our own backyard.”

Bottom line? The tsunami won’t look like this:

San Andreas movie tsunami

But, folks in California need to be aware of the potential for a regional tsunami.

Top image credit: Reuters (Tsunami impacting Japan in 2011)

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