In this multimethodological study, microstructural observations of fault rocks are combined with\udmicromechanical property analyses (contact resonance atomic force microscopy (CR-AFM)) and with rotary\udfriction experiments (Slow- to High-Velocity rotary-shear friction Apparatus apparatus) to find evidence of\udseismic to aseismic slip and understand the nanoscale rheology of clay-bearing, carbonate-hosted faults.\udFluidized structures, truncated clasts, pores and vesicles, and phyllosilicate nanosized spherules and tubes\udsuggest fast deformation events occurred during seismic slip, whereas clay-assisted pressure-solution\udprocesses, clumped clasts, foliation surfaces, and mantled clasts indicate slow deformation events occurred\udduring postseismic/interseismic periods. CR-AFM measurements show that the occurrence of ~5 wt % of clay\udwithin the carbonate-hosted gouges can significantly reduce the fault core stiffness at nanoscale. In addition,\udduring high-velocity friction experiments simulating seismic slip conditions, the presence of ultrathin\udphyllosilicate-bearing (≤3 wt %) layers within calcite gouges, as those observed in the natural fault, show\udfaster dynamic weakening than that of pure calcite gouges. The weak behavior of such layers could facilitate\udthe upward propagation of seismic slip during earthquakes, thus possibly enhancing surface faulting.\udMicrostructural observations and experimental evidence fit some well-known geophysical and geodetic\udobservations on the short- to long-term mechanical behavior of faults such as postseismic/interseismic\udaseismic creep, interseismic fault locking, and seismic slip propagation up to the Earth’s surface.
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