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DURING EARTHQUAKES, MINERAL GEL MAY REDUCE ROCK FRICTION TO ZERO
Researchers have discovered a mineral gel created when rocks abrade each other under earthquake-like conditions. If present in faults during a quake, the gel may reduce friction to nearly zero in some situations, resulting in larger energy releases that could cause more damage. Terry Tullis and David Goldsby of Brown University in Providence, R.I., and Giulio Di Toro of the University of Padova in Italy announce their findings in the Jan. 29 issue of the journal Nature. The researchers sheared quartz-rich rocks against each other under controlled conditions, simulating several aspects of a geologic fault environment. Future experiments will take advantage of a salvaged 100-horsepower BMW motorcycle engine, which will allow the apparatus to reach seismic slip speeds of one meter per second. As the shearing progressed, resistance between the rocks approached zero at the highest shearing speeds. Scanning electron microscope images suggest that mineral powder, in this case comprised of silica, generated during the abrasion combines with water from the atmosphere to form a gel that lubricates the rock surfaces. If confirmed with field observations, researchers could apply these findings to computer earthquake models. The simulations may help scientists and emergency personnel better predict the magnitude of strong ground motions that damage man-made structures. All three researchers were supported by NSF awards 0003543 and 0352548, and grants from the United States Geological Survey. Di Toro was also supported by an Italian MURST grant.
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