San Andreas Fault Cores Go Live, Online

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.