Project Abstract
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Zones of ‘pulverized rock’ have been observed in surface outcrops adjacent to the fault cores of the San Andreas and other major faults in Southern California. These pulverized rocks crumble in one’s hand, yet do not appear to have experienced significant strains, judging by the original grain
textures present in the rocks. The origin of these pulverized rocks is not clear. An understanding of their origin might allow inferences to be drawn about the nature of dynamic slip on these faults, perhaps including inferences concerning the coseismic resistance to slip. Brune [2001] has proposed that pulverization occurs at depth and results from normal vibrations on the fault surface during slip that involve reductions in normal stress and hence reductions in shear resistance. This proposal seeks to understand the origin of the pulverization by conducting experiments aimed at producing pulverized rocks in the laboratory under well-controlled conditions. Considerable
attention has been paid recently to the origin and significance of pulverized rocks, including a SCEC workshop [Evans et al., 2006] and associated field trip at the 2006 SCEC annual meeting [Dor, 2006]. There is a vigorous current debate concerning both the description and the origin of these rocks as is briefly outlined below. |
