Hi All. I found an interesting article about a discovery made by the University of Berkeley concerning the San Andreas fault and fluids and the source of those fluids. I still not sure that I fully understand the implications of this discovery, but somehow I don’t think it means we don’t have to worry about a major quake on the San Andreas fault.

The thing I wonder about is this related only to the San Andreas, or are there other faults that have the same fluids and if so is the source the same. Take Care…Don in creepy town

Scientists suspect that high-pressure fluids act as lubricants, making it easier for rocks in a fault zone like the San Andreas to be displaced. However, they need to know much more about these fluids, starting with the basic question: where do they come from? Two competing models attempt an answer. One says high-pressure fluids originate in the crust, seep into the fault zone and become trapped by mineral reactions. The other says these fluids originate in the mantle and get siphoned into the fault zone through the ductile base of the crust.

To test these models, Kennedy and Kharaka measured high-pressure fluids along the San Andreas fault for ratios of helium isotopes. To their surprise, they found ratios of the exceedingly rare helium-3 (helium with only one neutron) to common helium-4 (two neutrons) that were hundreds of times higher than the helium-3 to helium-4 ratios typically found in crustal fluids.

"Some of this fluid could have come only from the mantle," says Kennedy who believes that as fluids move upward from the mantle, helium-3 becomes increasingly diluted by the helium-4 that is common to the crust. This makes it difficult to determine the degree to which high-pressure mantle fluids contribute to the weakness of the San Andreas Fault, but the effect is thought to be large. The Kennedy and Kharaka study also raises the possibility that mantle fluid is flowing into the San Andreas Fault from great distances away.

• San Andreas Study