“Clusters of 0.5–8 ton boulders in the Atacama Desert (Sierra del Buitre, Chile) worn smooth around their midsections. It is suggested that this boulder smoothing is the cumulative result of at least 1 m.y. of rubbing between boulders during earthquakes. See “Seismicity and the strange rubbing boulders of the Atacama Desert, northern Chile,” by Quade et al., p. 851–854.
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Geology September 2012, v. 40, no. 9 (http://geology.gsapubs.org/content/40/9.cover-expansion)