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2.5 Mile Deep Hole Drilled Into San Andreas Fault
iandoh writes "Cool research: Geologists at Stanford University and the US Geological Survey have drilled a 2.5 mile deep borehole into the San Andreas fault. They've extracted over one ton of rock from 2 miles down, and they'll be installing sensors down the length of the borehole."
It does seem to be less than the record there. But we can hardly fualt (har har) the team for not digging the full 50 miles to the asthenosphere. :)
They drilled in a part of the San Andreas fault that creeps and doesn't generate big earthquakes. My take is that they're looking for a lubricant, something that allows the fault to slide. Another possibility would be merely that the fault doesn't have bends or splits in it unlike the faulting at the south end of the San Francisco Bay. The San Andreas fault runs along a chain of mountains south of Silicon Valley and then north through San Francisco, following the coast thereafter, while the Haywood fault runs along the base of mountains east of the Bay area from Milpitas to north of Oakland.
If a lubricant is responsible for the fault creep, there are apparently several possibilities: water, serpentine (which can be formed by weathering or metamorphization of several minerals including olivene/peridot), or talc (formed by serpentine exposed to water). If you have talc, you probably have the other two as well. Serpentine is a bit harder than talc (the latter is soft enough to easily scratch with a fingernail), but both deform easily under pressure. I seem to recall cases where serpentine has "bubbled up" over millions of years through denser rock, acting as a very slow moving fluid.
As I see it, if we can understand how to lubricate faults, then it is possible to not just trigger faults, but also to ease pressure on a fault. Maybe the cost of the materials will make it infeasible, but we can consider it now.