Where to see earthquake faults in the San Francisco Bay Area

Welcome to Bay Area Bucket List, where readers suggest things to do on the Bay and we go out and explore them. Have an idea for something to do (no skydiving, please) or a question you’d like answered? send it to us! Today Kathi C. asks:

Where are the earthquake faults? Anywhere we can see them?

Thanks for the question. The best way to see California’s earthquake faults is to go to HBO Max and stream “San Andreas,” a 2015 action movie starring The Rock and Paul Giamatti that’s holding up surprisingly well.

No seriously, fault line evidence is all around us – you just have to know what to look for. Here are some notable examples:

California Memorial Stadium

UC Berkeley’s Memorial Stadium sits on a major fault line. John Metcalfe/Bay Area News Group

When soccer players step onto the field at UC Berkeley Stadium, they actually run right over the Hayward Fault. This is a significant fault that cuts through the East Bay and is referred to as “tectonic time bomb‘ because some believe it is poised to explode with a large and damaging tremor.

Go up the stairs from Piedmont Avenue and then turn right until you are on the south edge of the stadium behind the KK seating area.

Here you can see a fist-sized gap running from the bottom of the stadium wall all the way to the top, where it seems someone tried to hold the two sections together with a thin strip of metal.

“Over time, this section of the Hayward Fault is creeping — it’s not waiting for a big earthquake to jump and move, it’s slowly creeping, creeping, creeping. And you can see the offset over time,” says Jennifer Strauss, external relations officer at the Berkeley Seismology Lab.

Normally you would never place a building on an active fault. But soccer is soccer, and you gotta protect America’s favorite pastime, I guess?

“After a while you can’t just let the stadium crawl on like that,” says Strauss. “So they had to do a rebuild (until 2012). That was a bit controversial because people were like, ‘Hey, maybe we’re not going to keep rebuilding the stadium on a fault that’s moving.’ Because it costs maybe half a billion dollars to reconstruct the stadium, and it’s not like you reconstruct it once and it’s done. It will continue.”

Look up at Cal’s Memorial Stadium and you can see the structure slowly creeping apart. (John Metcalfe/Bay Area News Group)

The engineering solution to this endless creep (at a rate of a few millimeters per year) was to install a variety of dampening devices and split the stadium in half so that the whole would not shatter in a tremor, but would instead move with it.

“Of course the stadium is used for games, so it’s not like there’s a big crack in the middle of the field,” says Strauss. “But on the outside of the stadium you can actually see that it’s in two parts, so the stadium stands can move relative to each other.”

For more information on where to find earthquake fun around the Berkeley campus, click here Self-guided hike through the Hayward Fault published by the seismology laboratory.

Point Reyes

John Metcalfe/Bay Area News Group

The earthquake of 1906 was so strong that it knocked a train from San Francisco bound for Point Reyes off the tracks. In the Point Reyes National Seashoreyou can see another sign of his immense power – a fence that “jumped” 16 feet in a matter of seconds.

Proceed to the visitor center parking lot and turn left to begin the Earthquake Trail, an easy 0.6 mile loop through fields and woods. Here you are at the heart of the San Andreas fault system, the grandfather of all Bay Area faults; the Hayward is part of this system.

The San Andreas stretches roughly from the Salton Sea in southern California to Cape Mendocino, where it empties into the ocean. It marks the place where the North American and Pacific tectonic plates inexorably grind past each other. About halfway down the Earthquake Trail you come to a fence that splits in two, a distance far enough to throw a baseball.

The 1906 earthquake was responsible for the 16-foot split in this fence line at Point Reyes National Seashore. (John Metcalfe/Bay Area News Group)

This is a replica of a historic barrier that likely demarcated a local ranch that was torn apart by the 1906 earthquake.

“This basically means there has been a lot of movement on one strand of the San Andreas fault system right there on the Earthquake Trail. It was the main breaking point for the earthquake in that area,” says Will Elder, a visual information specialist at the Golden Gate National Recreation Area.

Here’s a fun – well, quite frightening actually – illustration for kids, placed along the path, showing what would happen if they held hands during the quake:

An information board at Point Reyes illustrates the effects of the earthquake. (John Metcalfe/Bay Area News Group)

How active is the San Andreas Zone today?

“There are areas where it’s basically off-limits, and that’s the case in Point Reyes,” says Elder. “In the closed sections there appear to be large magnitude earthquakes – around 8.0 – and they occur every 100 to 300 years. Then on the decade scale there are smaller earthquakes in the sections where there is movement.”

The last major earthquake to hit Point Reyes was the big one in 1906. But who knows, that fence could soon jump another 16 feet. “The San Andreas is more than 100 years old,” says Elder. “So at some point it’s due — probably in the next 150 years.”

Say ponds and lagoons

Many of the large bodies of water in the North Bay from which we source our delicious oysters are also affected by fault activity.

https://www.mercurynews.com/2022/03/23/where-can-you-see-earthquake-faults-in-the-bay-area/ Where to see earthquake faults in the San Francisco Bay Area

Joel McCord

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