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Two fault systems thought to be separate are actually one. Yikes!

A new bit of anxiety producing research about two major fault systems in Southern California has just been released.  The two fault zones were always thought to be separate but now research has showed that they one continuous fault system running through San Diego, Orange and Los Angeles counties.

If all the offshore and onshore segments of the so-called Newport-Inglewood/Rose Canyon fault system were to rupture at once, a magnitude 7.4 earthquake could seize the region.

While previous research had suggested that breaks in the Newport-Inglewood and Rose Canyon faults were as wide as three miles, new research has found that these gaps were no more than 1.25 miles wide. The general belief is that the size of an earthquake is directly related to the length of the fault that’s rupturing — the longer the fault, the larger the earthquake.

Researchers spent more than 100 days at sea using acoustic waves to image the sedimentary layers of the seafloor. Combining this data with previous seismic surveys, the scientists were able to study the fault system at an unprecedented level of detail.

Their study, published this month in The Journal of Geophysical Research, was funded by Southern California Edison after the state government asked the utility to evaluate potential earthquake activity around its San Onofre nuclear power plant. For unrelated reasons, the plant is being decommissioned.

The fault is never more than four miles from the California coastline, and in some places — like Newport Beach and La Jolla — it runs under houses and other buildings. Over all, the fault moves and accumulates stress at less than one-tenth the rate of the nearby San Andreas fault.

Data suggest that the fault’s strands have not all ruptured simultaneously in more than 11,000 years. Portions of the fault have ruptured several times, however, including a magnitude 6.4 temblor in Long Beach, Calif., that killed 115 people in 1933.

https://www.nytimes.com/2017/03/27/science/earthquake-fault-line-southern-california.html?emc=edit_sc_20170327&nl=science-times&nl_art=&nlid=21404504&ref=headline&te=1

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