San Andreas Fault Cores = Go Live Online

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San Andreas Fault Cores Go Live, Online
Larry O'Hanlon, Discovery News


How It Works

       May 30, 2008 -- For the first time ever, the thrashed and jumbled innards of the notorious San Andreas Fault are now available online for anyone to see.
     The new Google Maps-based "Core Viewer" allows scientists and the general public to peer at high-resolution images of the rock cores drilled and extracted directly from the steadily slipping section of the infamous fault two kilometers (1.2 miles) beneath Parkfield, Calif.
     "That's where all the action is," said U.S. Geological Survey geophysicist Steve Hickman. At Parkfield, that action is already contorting the metal casing installed in the San Andreas Fault Observatory at Depth (SAFOD) borehole at a rate of two centimeters (0.8 inches) per year.
     The core viewer shows the fronts and backs of the long cylindrical rocks, marked in centimeters, drilled out with circular drill heads. The cores reveal two sub-faults of the San Andreas where rocks are currently being ground up by the sidewise meeting of the Pacific and the North American tectonic plates.
      The most important parts of the core show not only highly ground-up rocks, but rocks that have been polished by the shearing forces in the fault. There are also chunks of green rocks made of a very weak, slippery mineral called serpentine, which has long been a suspect in the lubricating of the San Andreas along this section in central California.
     "The serpentine is really an important find for us," said Hickman, referring to a section shown in the Core Viewer under Hole G, Run 2, sections 7 through 9. "It allows the fault to creep. The presence of that serpentine is kind of a smoking gun."
Section 8 of the same area reveals dark rocks that appear to shimmer like opals. These rocks were essentially ground smooth by the fault, like stones polished by a rock tumbler, Hickman explained.
      The bright white minerals in the same sections are calcite, a sign that water as been present and plays a role in the fault as well. These and other important sections of the core will be marked with bubbles containing scientific information as more work is done, Hickman told Discovery News.
     "The core viewer is to show the scientific community what the core looks like," said Stanford University's Charley Weiland, who serves as SAFOD's data manager. Already there are 800 samples requested from researchers who want to conduct all sorts of research on the rocks.
     "The core is a very scarce commodity," Weiland told Discovery News. The actual core is locked away at 4 degrees Centigrade with ocean drilling cores in a store facility in Texas, he said.
     SAFOD is one of three "observatories" encompassed by the EarthScope project. The other two are the Plate Boundary Observatory, which measures the ongoing tectonic mangling of the crust throughout the Western United States, and the U.S. Array, which is moving a high-density network of seismic stations across North America to uncover the physical structure of the continent.