 |
| Clinton Johnson/Bancroft Library |
| Quake-tilted homes in San Francisco, April 1906 |
 |
|
To understand California’s next big earthquake, you need to understand the last one. Given that scientists have been studying the 1906 quake for a century, you might think we already know all about it. Yet even basic knowledge of where the quake was centered has shifted: not beneath Marin County, the hypothesis for decades, but farther south, offshore from San Francisco. And there remain many other gaps in our understanding. This is why Jack Boatwright, a USGS geophysicist, found himself driving around the countryside north of San Francisco, looking for cemeteries near Sebastopol. He was trying to answer the question: How hard did the earth shake that April morning, and where did it shake most strongly?
Boatwright noticed that cemetery headstones were vulnerable in the 1906 quake. They toppled over. In many rural cemeteries, the fallen stones had never been replaced. By calculating the percentage of toppled versus upright pre-1906 headstones, Boatwright could determine how hard the ground shook.
 |
| James Chiang |
| USGS geophysicist Jack Boatwright scouted
cemeteries to unlock secrets of the 1906 quake. |
|
|
So Boatwright spent months scouring Northern California graveyards. He hired his daughter, Phoebe, then 9, to help. “I paid her a dime for every headstone before 1906.”Based in part on his gravestone research, Boatwright and his colleagues have produced a new Shake Map for the 1906 earthquake, showing in vivid color the intensities of shaking that California experienced. The results are unsettling. The Sebastopol area, for example, shook far harder than anyone would have predicted, given its distance from the quake’s epicenter.
You could look at this data two ways, Boatwright says. If you live right on top of the San Andreas, you may not be in as much trouble as you fear. “Or,” he adds, “if you live 30 miles away from the fault, maybe you shouldn’t feel too secure.”
