Microstructural evidence for seismic and aseismic slips along clay‐bearing, carbonate faults. Issue 5 (27th May 2017)

• Record Type: Journal Article
• Authors: Smeraglia, Luca; Bettucci, Andrea; Billi, Andrea; Carminati, Eugenio; Cavallo, Andrea; Di Toro, Giulio; Natali, Marco; Passeri, Daniele; Rossi, Marco; Spagnuolo, Elena
• Is Part Of: Journal of geophysical research. Volume 122:Issue 5(2017)
• Page Start: 3895
• Page End: 3915
• Publication Date: 2017-05-27
• Subjects: seismic cycle -- earthquake -- carbonate fault -- clay -- deformation mechanisms -- rotary experiments; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2017JB014042
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: In this multimethodological study, microstructural observations of fault rocks are combined with micromechanical property analyses (contact resonance atomic force microscopy (CR‐AFM)) and with rotary friction experiments (Slow‐ to High‐Velocity rotary‐shear friction Apparatus apparatus) to find evidence of seismic to aseismic slip and understand the nanoscale rheology of clay‐bearing, carbonate‐hosted faults. Fluidized structures, truncated clasts, pores and vesicles, and phyllosilicate nanosized spherules and tubes suggest fast deformation events occurred during seismic slip, whereas clay‐assisted pressure‐solution processes, clumped clasts, foliation surfaces, and mantled clasts indicate slow deformation events occurred during postseismic/interseismic periods. CR‐AFM measurements show that the occurrence of ~5 wt % of clay within the carbonate‐hosted gouges can significantly reduce the fault core stiffness at nanoscale. In addition, during high‐velocity friction experiments simulating seismic slip conditions, the presence of ultrathin phyllosilicate‐bearing (≤3 wt %) layers within calcite gouges, as those observed in the natural fault, show faster dynamic weakening than that of pure calcite gouges. The weak behavior of such layers could facilitate the upward propagation of seismic slip during earthquakes, thus possibly enhancing surface faulting. Microstructural observations and experimental evidence fit some well‐known geophysical and geodetic observations on the short‐ to long‐term mechanical behavior of faults such as postseismic/interseismic aseismic creep, interseismic fault locking, and seismic slip propagation up to the Earth's surface. Key Points: Fault microstructures record fast (seismic) to slow (aseismic) deformation stages consistent with some geophysical observations A few % of clays in natural fault gouge may strongly affect frictional behavior Shear experiments suggest that clay‐bearing layers have shorter weakening distance than carbonate‐pure gouges during seismic slip