Surviving The Big One

Hayward Fault hasn’t seen major earthquake since 1800s

Surviving The Big One

SAN FRANCISCO (KRON) — This summer’s magnitude 7.1 earthquake east of Bakersfield near Ridgecrest is a stark reminder that a similar earthquake can also happen in the Bay Area.

It’s also a reminder of just how long it’s been since the Bay Area experienced a major quake.

In fact, you have to go back five years to the Aug. 24, 2014 magnitude 6 earthquake in Napa.

Does that mean we are amid a major earthquake hiatus?

“Actually, in the Bay Area, we only rarely get magnitude 6 earthquake,” said U.S. Geological Survey Seismologist Andrew Michael.

Michael said it’s not that the Bay Area is on a hiatus from a big one, it’s that it’s unusual to see big quakes here.

“We only have magnitude 6 earthquakes once a decade. Sometimes we have several decades off without them,” he said.

In fact, in the 100 or so years following the 7.9 San Francisco earthquake of 1906, there have been just six earthquakes that are magnitude 6 and above.

In 1911, there was a 6.6 quake between San Jose and Morgan Hill.

In 1926, a 6.1 and a 6.3 quake struck off the coast near Pacific Grove.

Then almost 60 years passed before the most recent three: Morgan Hill’s 6.2 magnitude quake in 1984, the 6.9 Loma Prieta quake in 1989 and then 25 years later, 2014’s 6.0 quake in Napa.

Those three more recent earthquakes were all on different faults, Michael said.

The Napa earthquake was on a small network of faults, while the Loma Prieta was near the the San Andreas Fault.

The Morgan Hill earthquake was along the Calaveras Fault.

This leaves out the Hayward Fault, which hasn’t seen a magnitude 7 or higher earthquake since the 1800s.

“That’s the one we worry about because it runs though the most populated area in the East Bay and when it goes, it will create a lot of damage,” Michael said.

The earth’s surface is divided into plates and we get earthquakes when the pacific plate moves past the North American plate. 

Experts say part of the reason we get so few big quakes here in the Bay Area is due to our geography.

“The Pacific Plate is out here and it’s moving in this direction, parallel to the san andreas fault and parallel to the other faults and so the North American plate is moving this way so we have fairly smooth motion across these faults,” he said. 

Things are quite different in Southern California.

In fact down there, the San Andreas Fault takes a big bend.

“While the Pacific Plate here is moving here past the San Andreas, here it is running into it so this area is compressing, so that creates the mountains and also some extra earthquakes,” Michael said.

The key takeaway is even though those magnitude 6 and above quakes are few and far between, it  doesn’t mean they are not coming and it doesn’t mean you shouldn’t prepare for it.  


Below is a look at all of California’s fault lines.

Fault descriptions courtesy: U.S. Geological Survey

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