The earthquake that rattled Napa Valley and other parts of northern California on Sunday measured 6.0 on the magnitude scale.
That was the biggest quake in the Bay Area since the Loma Prieta earthquake in 1989 that caused severe damage in Santa Cruz, San Francisco, and Oakland, killing 63 people. That one measured 6.9.
So how did the two earthquakes compare in terms of actual shaking on the ground? The map below, put together by UC Davis geologist Dawn Sumner, shows the difference. The 1989 earthquake (on the right) had much,
much more shaking throughout the Bay Area: The 2014 Napa earthquake (magnitude 6.0) vs the 1989 Loma Prieta earthquake (6.9)
It's worth remembering that the scale geologists use to measure the energy released by an earthquake is logarithmic. That means that a magnitude 6.9 earthquake releases roughly 22 times as much energy as a magnitude 6.0 earthquake.
That said, the amount of ground shaking that actually happens depends on a variety of additional factors besides magnitude - the depth at which the earthquake occurs, the type of rock and soil in the region, as well as how the seismic waves propagate through the Earth's crust. Further reading:
David Perlman of the
San Francisco Chronicle has a good rundown of what geologists know about the 2014 Napa earthquake so far. The quake appears to have occurred along the West Napa Fault, a right-lateral strike slip fault. (Strike slip faults are common in California - in an earthquake, the sides on either side of the fault slip horizontally past each other.)
By contrast, the 1989 quake occurred further south - likely on an offshoot of the San Andreas Fault. Here's a rundown from the US Geological Survey of that earthquake.
Here's a helpful list of California earthquakes since 1989.
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