Superplastic nanofibrous slip zones control seismogenic fault friction

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Science  12 Dec 2014:
Vol. 346, Issue 6215, pp. 1342-1344
DOI: 10.1126/science.1259003

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Understanding the internal mechanisms controlling fault friction is crucial for understanding seismogenic slip on active faults. Displacement in such fault zones is frequently localized on highly reflective (mirrorlike) slip surfaces, coated with thin films of nanogranular fault rock. We show that mirror-slip surfaces developed in experimentally simulated calcite faults consist of aligned nanogranular chains or fibers that are ductile at room conditions. These microstructures and associated frictional data suggest a fault-slip mechanism resembling classical Ashby-Verrall superplasticity, capable of producing unstable fault slip. Diffusive mass transfer in nanocrystalline calcite gouge is shown to be fast enough for this mechanism to control seismogenesis in limestone terrains. With nanogranular fault surfaces becoming increasingly recognized in crustal faults, the proposed mechanism may be generally relevant to crustal seismogenesis.

Nanofibers involved in fault rupture

Changing fault properties during rupture dictates the size and extent of an earthquake. Faulting leads to well-known microstructures that may play a role in how natural faults slip during rupture. Verberne et al. investigated tiny, nanogranular fibers found in microstructures generated on simulated carbonate faults. A microphysical model was able to account for how the small and aligned fiber produced runaway fault slip, similar to that seen in natural faults. These small structures play a role in carbonate faulting and similar microstructures could control fault rupture in other types of rocks.

Science, this issue p. 1342

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