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Sun and Moon Nudge Deep Fault Tremor

A paper in the 24 December Nature shows that the deep crust can be an extraordinarily sensitive place: Deep in the San Andreas fault near Parkfield, California, nonvolcanic tremor responds to the daily tides raised by the Moon and Sun. This does nothing for the seismic syzygy theory beloved of geologist Jim Berkland (and debunked again and again) because actual earthquakes there have no such pattern. But it does suggest that the deep fault is in an exquisite balance between lithostatic pressure—the weight of the rock above—and the hydrostatic pressure of fluids in the fault zone. We already had a notion that this is true, because slow seismic waves from large, distant earthquakes also excite tremor here, but this adds independent evidence. The press release on this paper, from the authors' institution, UC Berkeley, is unusually lucid.

Sun and Moon Nudge Deep Fault Tremor originally appeared on About.com Geology on Wednesday, December 23rd, 2009 at 15:50:20.

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