The section of sidewalk curbing at the corner of Rose and Prospect Streets in Hayward, California had become the unofficial barometer of seismic activity in the region since the early 1970s.
It turns out that the corner curb had been built almost exactly on the Hayward fault line, one of many potentially dangerous faults that make up California’s geography. The Hayward fault’s activity has been visually measured, as seen in vintage photographs from 1971 to the present, as the curbing has pulled apart from the rest of the corner.
The Los Angeles Times describes the movement of the fault as being akin to someone pulling a tome off the bookshelf, disturbing the alignment of the neat row of books. But the curbing shows seismologists much more than a piece of sidewalk that has shifted.
Holy Grail to seismologists
The L.A. Times reports that by word of mouth, and later as social media became popular, the piece of curbing became a landmark of sorts, someplace that you had to come and see.
There is even a website, geologyfieldtrips.com, dedicated to the curb, with pictures documenting the movement of the fault line.
But one fine day in June, a city crew appeared, intent on fixing the faulty curbing, replacing it with a wheelchair accessible ramp, just like the 150 or so the city installs at street corners every year. While the city was only doing what city’s are supposed to do, fix streets — the repairs stunned earthquake scientists.
“They really took it out. Wow,” David Schwartz, a U.S. Geological Survey geologist, said when he clicked on a photo of the curb’s destruction. “It really was an iconic location on the Hayward fault.”
Oakland, Calif. science writer Andrew Alden documented the destruction of the curbing and was invited by the USGS to come to Hayward the last Friday in June, while a scientist was hoping to give emergency preparedness officials a look at “what a real fault looks like.”
Aiden’s blogs and posts were picked up by Canadian media as the story of the displaced curbing spread.
Fault creeping
The once straight curbing runs perpendicular to the Hayward fault which runs in a North-South direction parallel to its more famous westerly neighbor, the San Andreas Fault that also runs in a North-South direction offshore of San Francisco.
Over the years, the eastern half of the curb got pulled south, while the other side of the curb was pulled north. To the curious, and especially those who study earthquakes, actually measuring and documenting the sidewalk are proof of just how powerful the movements of the tectonic plates underneath the Earth really are.
The surface of the fault is creeping at a rate of about 0.5 centimeters (0.2 inches) per year, while the extreme southern region of the fault may creep a little faster. While the creep in not sufficient to prevent an earthquake, it will displace roads, sidewalks, fences and even cause fractures in the walls of buildings.
For those people who will say that a piece of sidewalk is not a good indicator of impending earthquakes, that is probably correct. But not everyone happens to have a seismograph sitting on the kitchen table. But for anyone interested in knowing just how strong the forces of nature are, then observing tectonics at work is a good place to start.
