Timothy Lesle

The following is part one of a three-part series of posts. You can download the entire text (without images) as one file here. It was reported in late 2007 and early 2008.

Hayward
Phil Stoffer squinted through the glass to see a sign of the past and, almost certainly, the future of this part of California. He knew what he was looking for and grinned when he found it. It was a crack, a big one. Stoffer held a hand near his wire-rimmed glasses to block the glare and traced the path of the crack as it ran along the high ceiling, then down a sea-green wall. Smaller cracks fractured the wall farther down and along a sweeping flight of stairs to the floor.

We were in Hayward, California, a small city across the bay from San Francisco, south of Oakland, north of San Jose. We stood in a little alcove pressing our noses against the outside of a modest side door. We were looking into what was, once upon a time, Hayward City Hall. It looked the part. It was an imposing concrete structure painted a sandy beige. It had a cornerstone inscribed MCMXXX and was decorated with geometric art deco flourishes and cornices shaped like the heads of cattle and goats. On one side of the building was busy Mission Boulevard, where Stoffer’s car was parked, and some landscaped grounds. Near its southern corner was a shiny, new playground where children swung back and forth through the air. There were a few other buildings on the block, but this one was abandoned, full of broken windows and old office equipment. Stoffer pointed out more cracks.

They were evidence of a much larger crack in the ground underneath. That crack is the Hayward Fault. Though the nearby San Andreas Fault is more famous, and much bigger, scientists like Phil Stoffer believe the Hayward poses a more imminent threat to northern California. Stoffer is a geologist with the U.S. Geological Survey who works from an office in Menlo Park, one of the small cities that make up Silicon Valley. Much of Stoffer’s current work entails mapping the remoter parts of Arizona’s Navajo reservations, where the geology is not overlain by development. But Stoffer had also been assembling a layman’s guide called “Where’s the Hayward Fault?”

The answer to that question is unsettling: the Hayward Fault is under one town after another along the eastern edge of San Francisco Bay. In his guide, Stoffer describes sites along the fault that are of historical or geological interest. He also highlights locations where locals can reach the fault by bicycle, foot, or mass transit (but not by car—it’s subtitled “A Green Guide to the Fault.”). The day we visited Hayward, we were going to add a few more sites to his guide.

This project is part of a larger effort this year to highlight the Hayward Fault. A group called the 1868 Hayward Earthquake Alliance is commemorating the 140th anniversary of a big earthquake on the fault. The alliance’s chairman is Tom Brocher, a senior USGS seismologist. If 140 is an unusual number for an anniversary, Brocher has his reason: “The Hayward Fault takes about 140 years to accumulate strain for a big earthquake. And that time has pretty well come and gone.”

Stoffer set off past the expansive set of concrete steps at the city hall’s main entrance and ambled along a cement sidewalk around the corner of the building. He carried a coffee cup and wore blue jeans and a plain gray sweatshirt with the initials USGS printed in small letters on the front. I followed him around the corner. Several feet in, the sidewalk on that side of the city hall abruptly shifted to the right, putting a kink into the straight ribbon of cement. It looked as if the workers who laid it down realized, after planting a few squares of cement, that they had misread the plans by a couple of inches.

In a parking lot full of cars north of the old city hall, Stoffer pointed to a red brick building with dozens of metal plates screwed into the walls. “Classic retrofit,” he said. He continued north and admired several curbs that had been either cracked or warped severely, each one veering to the right and then straightening again, as if correcting course. We stopped in another parking lot and Stoffer paced back and forth along a series of cracks in the asphalt, each about a foot long. The cracks were parallel to each other and scudded along an invisible line through the parking lot, like the wrinkles at the corner of a smile or a string of Christmas lights.

“These are en echelon cracks,” Stoffer said. They had formed because the Hayward Fault was directly underneath the parking lot. As the chunks of earth on either side of the fault crept past each other, the moving earth tugged at the asphalt above, cracking it. The fault also created the kink in the sidewalk, and the bent curbs; it’s the reason the old city hall was cracked and abandoned.

Stoffer swung his arm roughly northwest to southeast, indicating the trend of the en echelon cracks. They emanated from a small shop next to the lot, On Time Signs. Stoffer opened the door, a little bell rang, and soon a young woman appeared at the counter, asking if she could help us. Stoffer needed information: “Do you make neon signs?”

They did. He asked how much it might cost to make a little green dinosaur. He had been toying with an idea for another project, which he declined to describe. He asked how much neon lettering costs. The woman told him that the price depends on the number of bends it takes to make each letter. He asked her what she thought of working on top of a fault.

A couple of weeks earlier, an earthquake occurred near San Jose, on yet another Bay Area fault, the Calaveras. The Bay Area took notice—it had a magnitude of 5.6 and was felt throughout the region. The next day, the San Francisco Chronicle warned that this quake increased the chances of earthquakes “along the much more dangerous Hayward Fault.” Stoffer thought of it as the “perfect” earthquake. Perfect because it did so little damage, yet was big enough to be widely felt and covered by all the local media. It reminded locals that they live among active faults. And it gave Stoffer and his colleagues an opportunity to talk about the threat posed by the Hayward Fault, as well as the need to be prepared.

“It’s a concern,” the woman behind the counter answered. “But what are you going to do?”

Lake Temescal

Stoffer wanted to visit Lake Temescal to take some photos for his guide. He had some trouble getting there. Most of that trouble came from other cars. It was a long drive from Hayward to this little corner of a long valley tucked into the exclusive hill neighborhoods of Oakland. He drove a red Subaru wagon with a Darwin fish affixed to the back. Stoffer had to swerve mightily to avoid being sideswiped by a truck as he drove onto highway 254, then got caught in a jam on interstate 880, surrounded by rumbling tractor trailers bound for the nearby Port of Oakland. He negotiated the traffic and switched onto the 980. “Look at this tangle of freeways,” he said as he passed under a knot of freeway interchanges that rose two, three, and four stories into the air. Here the 980 met the 580 and became state highway 24. “Would you want to be here during a major earthquake? I assume it’s built to code.”

The exit for Lake Temescal was poorly marked. Stoffer’s first glimpse of it was at 40 miles per hour as he zipped past, consequently merging from highway 24 onto the Warren Freeway. He took the nearest exit and hooked onto a street called Broadway Terrace; it shunted us up a steep hill and into the affluent upper Rockridge section of Oakland. Far below were Lake Temescal and the fault.

Stoffer drove down the other side of the hill, passing huge homes. He followed the road through a golf course and stopped at a crosswalk to let a golf cart cross to the next hole. As he circled back to Lake Temescal, he craned his head over the dash to better examine the pavement ahead of him. “Gosh, those cracks running down here are pretty suspect.”

After a few more turns, Stoffer pulled into the parking lot at Lake Temescal. One side of the lot was hemmed in by a steep hillside—the same hill Stoffer had just crested. At the very top was a house that looked like it was built on the crowns of the trees below it. A little push, it seemed, and the house might tumble into the lot.

Stoffer rummaged in the back seat and pulled out a tripod and a pair of small digital cameras, which he screwed onto a metal bar on the top of the tripod. As part of his field guide, he was also including 3-D photographs of cracks, buildings, or the scenery—thus the twin cameras, which, like a pair of eyes, would produce a stereoscopic view. He walked over a green, manicured knoll to get a better view of the lake.

Temescal is a sag pond , dammed at one end to hold water, that formed in a depression in the ground—a sag—created by the Hayward Fault. During hot summer days, it is a popular swimming spot. On its northeast shore is a small stretch of beach and nearby is a stone house built by the Works Progress Administration.  But that November morning, the kids who might otherwise be found there were in school at nearby Chabot Elementary and College Prep. The lake was quiet, its surface interrupted only by a few ducks. A light fog hung overhead, and the leaves on some of the trees had turned. It looked like a Hudson River School painting.

Stoffer took a couple of snapshots and then strode across the grass in search of signs of the fault. He studied several cracks in a paved hiking path, but didn’t think they showed anything. He wandered closer to the highway and sized up several ruptures in the pavement. Tree roots, he decided.

The Hayward Fault runs along the length of this valley. It’s believed to be the reason the valley exists, its motion enabling the forces of erosion to carve the valley out more easily.  But Stoffer was searching for signs of creep. He wasn’t having any luck.

The blocks of earth along the three miles of the fault just below the surface tend to move past each other slowly, on the order of a few millimeters per year.  That motion, or creep, can often be detected as it damages all the stuff people build above the fault—like downtown Hayward. (Unsatisfied with our initial survey, Stoffer went back to Lake Temescal and found en echelon cracks and an old rail tunnel that had been offset by creep at the lake’s southern end.)

“The little effects,” Stoffer said, “aren’t anything tremendous. But it’s an amazing story.” Still, those little effects are only the faintest harbingers of the fury buried miles below the surface. The fault extends about eight miles below ground,  and the sections of earth along the fault below the three-mile mark—the part that’s not creeping—are stuck to each other. Because they aren’t moving, they are building up the stress that fuels a big earthquake.

Tom Brocher, the USGS seismologist, visualizes the earth on either side of that deep section of the fault as a pair of metal sheets similar to those seen on roads. They lie flat, and are pressed together along their thin edges. At a few places, those sheets are welded together—in geological terms, those spot welds are called asperities. “And somebody has grabbed these plates and tried to rip them apart,” Brocher said in an interview in his office. His hands pantomimed someone struggling to open a stuck drawer. “For a while, those welds will hold. But eventually they break. And that’s the earthquake.”

A recent USGS map shows many of the fault’s active surface traces, a series of bold red lines that underlie homes and offices and roads.  But in some places, like Lake Temescal, the line peters out, replaced by a timid little thread showing where the trace of the fault probably is.  Stoffer wouldn’t be making that red line any bolder the day he visited.

“This would be a good place to come after a major earthquake,” he said, as he walked back to his car. “At least you’d have water.”

Next: Background on the Hayward Fault, potential damage from Hayward quake, and the Claremont Resort.

By Tim | 11th June 2009 at 7:32 am
Filed under: earth
Tags: 1868, Bay Area, california, geology, Hayward, Hayward Fault, Phil Stoffer, ruins, sag pond, strike-slip, Temescal, Tom Brocher