The intensity of shaking felt during Sunday’s magnitude-6.0 earthquake centered in Napa appears to have rivaled the motion felt at the epicenter of the Northridge magnitude-6.6 earthquake in 1994.
An estimate posted on the U.S. Geological Survey’s website put the Napa earthquake’s shaking intensity as level IX, which is classified as “violent” perceived shaking at the epicenter. There is only one level intensity higher than level IX, which is level X, which would be classified as extreme.
The perceived shaking during the Northridge quake was also a level IX.
Intensity of shaking is different than the magnitude, which is a number that represents total energy released during an earthquake.
It’s possible, however, that the intensity level could be downgraded later by the USGS, said state geologist John Parrish.
It’s important to point out that there was far more land that suffered from intensity IX shaking during the Northridge earthquake than in the Napa area, Parrish said.
“There has been substantially less damage in the Napa area than there was at Northridge,” Parrish said.
A day after the Napa temblor, inspectors had deemed 70 buildings here uninhabitable. The number of people treated for injuries had risen to 208, and schools remained closed. The Northridge quake was much more destructive and killed about killing about 60.
Napa residents described the shaking Sunday morning as so violent, they described struggling to get out of bed.