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Figure 4

From: Ultra-thin clay layers facilitate seismic slip in carbonate faults

Figure 4

Experimental microstructures. (a) Left: FE-SEM image of dry layered gouge experimentally-sheared at subseismic velocity (0.001 ms−1). Grain size reduction occurs toward the principal slip zone. Inset shows a detail of phyllosilicate lamellae showing no nanospherules or nanotubes that occur, in contrast, in samples from experiments at seismic velocity (see d). Right: EDS map showing no concentration and segregation of phyllosilicates along distinct layers that occur, in contrast, in samples from experiments at seismic velocity (see b–d). FE-SEM image of (b left) wet mixed gouge experiment and (c left) wet layered gouge experiment sheared at seismic-slip velocity (1 ms−1) showing grain size reduction toward the principal slip zone. EDS map shows segregation and concentration of phyllosilicates along micrometer-thick layers both for mixed (b right) and for layered (c right) gouges under wet conditions. Insets show carbonate clasts within phyllosilicate-bearing layer wrapped by phyllosilicates. (d) Left: FE-SEM image of dry layered gouge experiment sheared at seismic-slip velocity (1 ms−1) showing, toward the principal slip surface, grain size reduction and compaction stronger than wet gouges. Inset shows the nanostructures from the principal slip zone. These structures consist of clumped and chained nanospherules and nanotubes identical to those observed within phyllosilicates along the Tre Monti principal fault (see Fig. 2e and f). Right: EDS map showing concentration and segregation of phyllosilicates along a micrometer-thick layer.

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