Why you should see the Hayward fault in person

Earthquakes have always shaken the Bay area, but for thousands of years residents have lived with them. Today we’re better off than any of our predecessors: we know just where the faults that cause earthquakes are located. We know where the ground is likely to rupture, and we even have some idea of when.

I submit that now is a good time to get to know the Hayward fault, and understand it a little better, before the next time it disrupts our lives. Though earthquake faults may be objects of dread, they’re safe to approach today, while they sleep (except for a little bit of creep).

The Hayward fault stretches from Point Pinole in Richmond to Alum Rock in San Jose, and its telltale signs aren’t hard to learn: lines of roadway cracks, skewed buildings, bent curbs, odd landforms. The fault may be hiding in plain sight, but it’s not a secret.

Since humans first arrived during the latest ice age, Bay area residents have known the land is prone to large, unpredictable earthquakes. The Indigenous tribes knew. The Spanish explorers and Mexican colonists who followed were not surprised, from long experience in their homelands. But starting in 1849, the Gold Rush brought a wave of naive outsiders to the Bay area. If the newcomers heard Mexican old-timers tell about the great shock of 1838 in Monterey, well, those were just stories, not experiences: there and then, not here and now.

Soon enough, California gave notice of its nature when the massive quake of 1857 shook the state from end to end. After that, major seismic events in the Bay area came hard and often. The newcomers wised up and adapted. Between 1858 and 1898 the Bay region experienced ten more earthquakes of at least magnitude 6 — the size of the Napa earthquake in August 2014. The largest of these, the “great San Francisco earthquake” of 1868, was the last big rupture on the Hayward fault.

By that time, builders in the young cities of the Bay area had learned to keep structures strong and low, no higher than three or four stories, to resist the effects of shaking. During the 1868 earthquake, the brand-new Wilcox Building, the tallest in Oakland at three stories, survived undamaged thanks to heavy iron bracing and still stands today at 9th Street and Broadway.

San Jose’s county courthouse also weathered it well. Architects had learned firsthand how to meet the demands of earthquake country.

The 1906 San Francisco quake, a great rupture of the San Andreas fault, gave birth to modern earthquake science. In the century that followed, California geologists learned to read the landscape in terms of tectonic movements along specific faults, active cracks in the earth’s crust. Today seismologists monitor active faults around the clock. Our phones can alert us to significant Bay area earthquakes before the shaking even arrives. Architects design quake-resistant structures, and building codes mandate them. We have good tools for living with earthquakes.

However, the Bay area faults have been much quieter than they used to be, producing only four magnitude-6 events in the last hundred years, none of them with epicenters in the central Bay area. During that century, the Bay area’s population has grown more than six times larger, and relatively few residents have ever experienced damaging shaking.

This matters especially for the East Bay, where cities grew up directly on the Hayward fault for decades before geologists mapped it. Modern practices have offset some of the resulting risk. But when the next big rupture happens on the fault — geologists put the odds during the next 20 years at about one in three — the region will be severely tested. As many as a million buildings in the greater Bay area will suffer damage, and tens of thousands of people will be displaced. It’s urgent to cope with this prospect in advance, but the task is not easy or simple.

We can’t depend on the Earth to keep reminding us about earthquake-resistant living. There’s a lot of slow, hard work yet to do — retrofitting or replacing vulnerable structures, teaching good practices to children and new residents, and maintaining disaster preparedness. The drive to sustain that work has to be embedded in our culture, generation after generation.

It’s easy to fear our active Hayward fault, and plenty of media stories reinforce the dread, but fear may not be the best long-term motivator. I believe that seeing this sleeping giant and taking its measure in person can help change attitudes. Two good places to see its marks on the landscape, with interpretive signs, are at Lake Temescal Regional Park in Oakland and in Fremont’s Central Park.

Geologists are wary of the Hayward fault, like the rest of us, but they also regard it with wonder and respect. They see the fault as an ancient channel of energy that has built our beautiful landscape over millions of years and maintains the landscape with each earthquake. As the Indigenous tribes might put it, Earthquake is our uncle, part of the country, who has a seat among us at the evening fire, and the Hayward fault is the place where it wakes and sleeps.

2 Responses to “Why you should see the Hayward fault in person”

  1. John Rummel Says:

    Andrew, thank you for the book and for this website. I’m a geology nerd and have extensively road-tripped the SAF to see the best examples of surface manifestation of the fault. I have also visited Hollister a couple of times to see the great examples of creep along the Calaveras. I have extensive notes on the Hayward fault but have not yet had a chance to spend the two to three days necessary in the East Bay to really visit all the good sites. When I saw your book drop, I was glad I waited. Regarding the book, I have to say I appreciate your cultural sensitivity as much as I do the sharing of your geology knowledge. I can’t wait to visit this summer with the book in hand and give the Hayward its due. Thanks again.

  2. Chris Bryant Says:

    Hi Andrew,

    Thanks for all your writings and insights. In your new blogpost, the style of faulting in the first photograph looks awfully left-lateral to me. Am I wrong, is the photo flipped, or does the Hayward fault somehow actually express itself left-laterally in some locations?

    Again, thanks for the knowledge. Chris Bryant


Leave a reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: