Experimental fault zones developed in Carrara marble that were deformed at seismic slip rates (1.18-1.30ms-1) using a high-velocity-rotary-shear apparatus exhibit very low friction (friction coefficient as low as 0.06) at steady state due to nanoparticle lubrication of the decomposition product (lime). The fault zones show a layered structure; a central slip-localization layer (5-60μm thick) of lime nanograins mantled by gouge layers (5-150μm thick) and a plastically deformed layer (45-500μm thick) between the wall rock and gouge layer in the marginal portion of cylindrical specimens. Calcite grains of the wall rock adjacent to the slip zone deform by dislocation glide when subjected to frictional heating and a lower strain rate than that of the principal slip zone. The very fine (2-5μm) calcite grains in the gouge layer show a foam structure with relatively straight grain boundaries and 120° triple junctions. This foam structure is presumed to develop by welding at high temperature and low strain once slip is localized along the central layer. We suggest that a seismic event can be inferred from deformed marbles, given: (i) the presence of welded gouge with foam structure in a fault zone where wall rocks show no evidence of thermal metamorphism and (ii) a thin plastically deformed layer immediately adjacent to the principal slip zone of a cataclastic fault zone.
Bibliographical noteFunding Information:
We thank William Dunne, Kyu Kanagawa and an anonymous reviewer for their constructive comments which improved the paper. The observations of the experimental specimens were made using TEM (JEOL JEM-2010) housed at the Natural Science Center for Basic Research and Development of Hiroshima University, FE-SEM (JEOL JSM-7000F) at Geodynamics Research Center of Ehime University and FE-SEM (Hitachi S4300) at the Korea Basic Science Institute, Seoul. This work was funded by a research grant of Korea Hydro and Nuclear Power Co. Ltd. to Ree.
Copyright 2014 Elsevier B.V., All rights reserved.
- Carrara marble
- Coseismic microstructure
- High-velocity-rotary-shear apparatus
- Seismic faulting
- Thermal decomposition
- Welded gouge
ASJC Scopus subject areas