Geology of the Napa Valley Earthquake
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The article linked above at IO9 is informative and packed full of information. A short quote:

Californians woke up to the largest earthquake in the Bay Area since the infamous 1989 Loma Prieta interrupted the World Series and collapsed the Bay Bridge. While the human cost is relatively low — dozens of injuries reported with no fatalities — the epicentre in the heart of wine country and its historic buildings will make this an expensive disaster.

[…]
While the San Andreas Fault is a specific fault line, it’s also the collective name for a 70-kilometer wide shear zone of individual cracks and faults along the boundary between the two plates. The entire fault system is nearly 1,300 kilometers long, and extends at least 15 kilometers deep into the crust.

Within the Bay Area, the main San Andreas Fault cuts through San Francisco and sections off Point Reyes. Many other faults within the zone are also prominent and active enough to earn names — the Hayward Fault shows up in real estate paperwork, and Rodgers Creek shares a name with a Vineyard. Many of these faults, like San Joaquin and Green Valley, are the structural underpinnings of the long valleys characteristic to the region. Even more faults don’t have names at all, especially if they haven’t had major damaging activity in the recent past.

[…]

It’s impossible to predict the exact timing of an earthquake, but we can take advantage of the different velocities of seismic waves to create earthquake early warning systems. Systems already exist in Japan and Mexico, but California does not yet have a functional, funded system.

For anyone interested in both the science of earthquakes and surviving them, this article is highly recommended.

More at links above

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