California protected from bigger quakes by talc deposits

Dermatology for tectonic plates, no less. Three kilometers under the central San Andreas Fault, talc deposits are reducing friction between the plates. Apparently the northern and southern tips are the culprits for the big quakes.

Talc is the softest mineral, with a hardness rating of 1. Diamonds are 10. It’s used to reduce friction on everything from babies’ bottoms to machinery. It bonds in platelets to give an oil-like feel. The San Andreas Fault is one of the best known, most researched, and complex big fault lines of all. It represents the split between the North American Plate and the Pacific Plate. From which you might gather that’s a lot of talc we’re talking about, and it’s affecting the behavior of uncounted millions of tons of rock. This Nature piece is a bit short on detail, but it has a new take on the physical processes of plate movement. The stick and slip effect, which creates big quakes due to sudden releases of pressure when plates move, is apparently much reduced by talc. With the talc underneath, the plates still move, but without building up as much pressure. (Note: Nature is a subscriber magazine. The link leads to an article, but doesn’t give full access.) In fact the stick and slip problem might well be being avoided. Interestingly, the person researching the subject originally wasn’t looking for talc, but another mineral, called serpentine, which he’d thought would have this effect. Serpentine is thought to be responsible for a slow creep of plates in much the same way the talc operates, but the talc is more effective. Typically, the San Andreas Fault hasn’t given up all its secrets. This is only one part of the Fault, and the other sections still aren’t talking.