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Southern California could be hit by major earthquakes and tsunamis, if little-researched offshore fault lines are as active as geologists think.

New research led by geologist Mark Legg, and to be published in the Journal of Geophysical Research: Earth Surface, found that movement along the Santa Cruz-Catalina Ridge Fault and the Ferrelo Fault could mean 7.9 to 8.0 magnitude earthquakes in the region. So that sucks.

O'Hanlon

Image via AGU.

And back in March, the U.S. Geological Survey reported that the likelihood that a magnitude 8 (or larger) earthquake will hit California in the next 30 years has gone up. The lead author of that study, Ned Field, pointed out at the time that the major earthquakes could be prompted by multiple faults, saying "the new likelihoods are due to the inclusion of possible multi-fault ruptures, where earthquakes are no longer confined to separate, individual faults, but can occasionally rupture multiple faults simultaneously."

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Image via the U.S. Geological Survey.

Legg and his colleagues found that both the Santa Cruz-Catalina Ridge Fault and the Ferrelo Fault showed signs of having shifted — which means they could again. And if they do, they could cause quakes or tsunamis.

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The American Geophysical Union (AGU) explained in a press release how Legg and his co-authors reached their conclusion:

By combining older seafloor data and digital seismic data from earthquakes along with 4,500 kilometers (2,796 miles) of new seafloor depth measurements, or bathymetry, collected in 2010, Legg and his colleagues were able to take a closer look at the structure of two of the larger seafloor faults in the Borderland: the Santa Cruz-Catalina Ridge Fault and the Ferrelo Fault.

There’s a reason Legg is piecing together years-old data to figure out what’s going on off the California coast. Per the press release, NOAA was in the process of putting together a bathymetry (which looks at underwater topography) of the U.S. Exclusive Economic Zone, or the swath of ocean under American jurisdiction. Then, NOAA's budget was cut, and the project stalled.

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Seems like that would have been money well spent.

Danielle Wiener-Bronner is a news reporter.