Listening to the San Andreas

Discover what today's scientists are learning about the earthquakes to come

Listening to the San Andreas

The San Andreas cuts past the Temblor Range in California’s San Luis Obispo County.

Michael Collier

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  • Listening to the San Andreas

    Quake-tilted homes in San Francisco, April 1906

  • Listening to the San Andreas

    USGS geophysicist Jack Boatwright scouted cemeteries to unlock secrets of the 1906 quake.

Take a flight between Los Angeles and San Francisco and you see it about the time you finish your peanuts. Below you, running across central California, a scar as vivid as any caught on a plastic-surgery show like Dr. 90210 or Extreme Makeover. The San Andreas Fault.

One hundred years ago this month, the San Andreas changed history. The earthquake that struck the San Francisco Bay Area at 5:12 a.m. on April 18, 1906, shattered cities, helped create modern earthquake science, and established the image of California as a Marilyn Monroe-like place where seductive beauty joins with fatal instability.

A century later, earth scientists are uncovering the secrets of San Francisco's extreme makeover and the fault that caused it. "Like the San Andreas itself, our understanding of it has been locked," says Mary Lou Zoback, senior research scientist at the U.S. Geological Survey. "Now it is starting to move."

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.

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."


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