Silicon Valley Mansions, Swallowed Alive
The signs that something’s wrong are not immediately obvious, but, once you see them, it’s hard to tune them out. Curbs at nearly the exact same spot on opposite sides of the street are popped out of alignment. Houses too young to show this kind of wear stand oddly warped, torqued out of sync with their own foundations, their once-strong frames off-kilter. The double yellow lines guiding traffic down a busy street suddenly bulge northward—as if the printing crew arrived to work drunk that day—before snapping back to their proper place.
This is Hollister, California, a town being broken in two slowly, relentlessly, and in real time by an effect known as “fault creep.” A slow, surreal tide of deformation has appeared throughout the city. As if the houses were actually built on an ice floe, the entire west half of Hollister is moving north along the Calaveras Fault, leaving its eastern streets behind. In some cases, doors no longer fully close, many windows now open only at the risk of getting stuck and a few no longer close at all. Walking through the center of town near Dunne Park offers keen observers a hidden funfair of skewed geometry.
Go to the house at 359 Locust Avenue. The house itself is on a different side of the fault than its own front walkway, pulled inexorably north as if trapped on a slow conveyor built beneath the street, with the effect that the path is now nearly two feet off-center from the porch it still (for the time being) leads to. In another generation, it will be useless, leading visitors straight into a pillar.
Or walk past the cute Victorian at 570 5th Street. Strangely askew, it seems frozen at the start of an unexpected metamorphosis, an architectural dervish interrupted before it could complete its first whirl. Geometrically, it is a cube being forced into a rhomboid by the fault.
Now look down at your feet at the ridged crack spreading through the asphalt behind you, perfectly aligned with the broken curbs and twisted houses on either side. This is the actual Calaveras Fault, forcing its way through town, bringing architectural mutation along with it.
There’s much more. Stop at the north end of 6th Street, for example, just across from Dunne Park, and look at the half-collapsed retaining wall hanging on for dear life in front of number 558. It looks like someone backed a truck into it—but it’s just plate tectonics bulging northward without regard for bricks or concrete.
So what’s happening to Hollister? “Fault creep” occurs when the underlying geology is too soft to get stuck or to accumulate stress: in other words, the deep rocks here are slippery, more pliable, and behave more like talc. The ground sort of oozes past itself, a slow-motion landslide at a pace that would be imperceptible if it weren’t for the gridded streets and property lines being bent out of shape
The good news is that the large and damaging earthquakes associated with fault movement—when the ground suddenly breaks free every hundred years or so in a catastrophic surge—are not nearly as common here. Instead, half a town can move north by more than inch every five years and all that most residents will feel is an occasional flutter.
I spoke with Andy Snyder from the U.S. Geological Survey about the phenomenon. For Snyder, the state of California is a sprawling geological wonderland to be understood through stress-field diagrams, topographical maps the colors of tie-dye, and delicate instruments installed carefully at sites of seismic vulnerability. Snyder works on an experiment known as the San Andreas Fault Observatory at Depth, or SAFOD, which has actually drilled down through the San Andreas Fault to monitor what’s happening there in the endless pressure and darkness, studying the landscape from below through sensitive probes installed deep in the active scar tissue between tectonic plates.
On Snyder’s advice, I made my way out to one of the more awesomely mundane monuments to fault creep in the state of California. This was in Parkfield, a remote town with a stated population of 18 where Snyder and SAFOD are both based, and where fault creep is particularly active. In Parkfield there is a remarkable road bridge: a steel structure that has been anchored to either side of the San Andreas Fault like a giant, doomed staple. Anyone who crosses it in either direction is welcomed by signs onto a new tectonic plate—but the bridge itself is curiously bent, warped like a bow as its western anchorage moves north toward San Francisco. It distorts more and more every day of the month, every year, due to the slow effects of fault creep. Built straight, it will someday be a graceful curve.
Parkfield is approximately where fault creep begins in the state, marking the southern edge of a zone of tectonic mobility that extends up roughly to Hollister and then begins again on a brief stretch of the Hayward Fault in the East Bay.
Indeed, another suggestion of Snyder’s was to visit a very specific corner in Hayward where a curb at the intersection of Rose and Prospect Streets has long since been shifted out of alignment. Over the past decade—most recently, in 2011—someone has drawn little black arrows on the concrete to help visualize how far the city has drifted in that time. The result is something like an alternative orientation point for the city, a kind of seismic meridian or doomsday clock by which Hayward’s ceaseless splitting in two can be measured.
If seismic energy and plate tectonics both sound too huge to imagine—of vast earthquakes and titanic cracks appearing in the Earth’s surface—then it can be quite surprising to learn that even the tiniest of details hidden in plain sight, such as curbs, broken water mains, and tilting front porches, can actually be real-time evidence that California is on the move. But it is exactly these easily missed details that are the minor landmarks of the seismic tourist—and, for all their near-invisibility, visiting them can be a mind-altering experience.
Back in Hollister, however, Snyder warned me that many of the already subtle signs that make fault creep visible are becoming less and less easy to find. The town is rapidly gentrifying. Hollister’s population is growing as its leafy streets fill up with commuters who can no longer afford to live closer to the Bay. This means that the city’s residents are now just a bit faster to repair things, just a bit quicker to tear down structurally unsound houses. One of the most famous examples of fault creep, for example—a twisted and misshapen home formerly leaning every which way at a bend in Locust Avenue—is gone. But whatever replaces it will face the same fate.
After all, the creep is still there, like a poltergeist disfiguring things from below, a malign spirit struggling to make itself visible. Beneath the painted eaves and the wheels of new BMWs, the landscape is still on the move; the deformation is just well hidden, a denied monstrosity reappearing millimeter by millimeter despite the quick satisfaction of weekend repair jobs. Tumid and unstoppable, there is little that new wallpaper or re-poured driveways can do to disguise it.
Snyder remembered one more site in Hollister he urged me to visit. Fault creep is not without its benefits, he said. In the very center of Hollister’s Dunne Park, a nice and gentle swale—“like a chaise longue,” in Snyder’s words—has been developing. Expecting to find just a small bump running through the park, I was surprised to see that there is actually a rather large grassy knoll, a rolling and bucolic hill that few people would otherwise realize is an active tectonic fault.
In fact, he said, residents have been entirely unperturbed by this mysterious appearance of a new landform in the middle of their city, seeing it instead as an opportunity for better sunbathing.
Snyder laughed, describing the sight of a dozen people and their beach towels, all angling themselves upward toward the sun, getting tan in a moving city with the help of plate tectoni