The earthquake in 2014 took the lives of two people and damaged more than 2,000 structures.
The west Napa Fault runs north to south from Saint Helena to Vallejo nearly parallel to Highway 29.
Scientists say its potential to cause major damage is greater than they anticipated.
USGS researchers have been working to better understand the fault system. A fault is a fracture or zone of fractures between two blocks of rock.
Faults allow the blocks to move relative to each other and the movement may occur rapidly, in the form of an earthquake. Now one of those researchers, Belle Philibosian, has discovered that the West Napa Fault stretches approximately 9 miles farther North than previously thought.
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Stephen DeLong is a Research Geologist at the USGS and colleagues with Philibosian.
"Because we think it's a longer fault that means it may be able to release more energy in an earthquake," said DeLong.
In essence, more shaking.
Yusuf Topal owns Tarla Grill in Napa. In 2014, he owned Napkins Bar and Grill in downtown Napa. He described the damage his business sustained from the 6.0 quake.
"If the earthquake happened an hour before we had hundreds of people leaving the bar, so it will be huge damage for all of our guests and maybe employees as well," said Topal.
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As for the news the Napa fault line is longer than previously suspected --
"Definitely, it makes me anxious," said Topal.
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Still DeLong says the West Napa Fault is considered a secondary fault or a minor fault compared to others in the Bay Area.
"It is an active fault, it will have more earthquakes but it certainly not as big a player as the San Andreas Fault or the Hayward fault," said DeLong.
DeLong says any of the faults in the Bay Area can have an earthquake at any time.
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And while researchers are adept at studying fault lines, what they can't do is predict when earthquakes will occur.
"It certainly is a reminder that any of the faults in the Bay Area can have an earthquake and anyone who lives in the greater Bay Area or really in California should have a plan to be prepared for strong shaking due to earthquakes," said DeLong.
DeLong says the new research isn't a big change in how researchers think about the hazard of the West Napa fault.
Click here for the latest stories and videos about earthquakes here in the Bay Area and around the world, and click here for more information on disaster preparedness.
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