The role of shear fabric and normal stress on the mechanics of slow-slip
Abstract
Seismic and geodetic observations show that fault slip occurs via a spectrum of behaviors that include slow earthquakes. These phenomena have been observed in a variety of tectonic environments worldwide, however the underlying processes are poorly understood. Here we show results from lab experiments on simulated fault gouges such as quartz and a mixture on anhydrite and dolomite. Using the double direct shear configuration we obtain slow-slip events varying the loading system stiffness (k) to match the critical fault rheologic stiffness (kc) (i.e., k kc). We find that the stress drop, micromechanical deformation (i.e. dilation/compaction), and the slip velocity (duration, shape and peak value) during the slow-slip events depend on how shear localizes within the fault gouge. For quartz gouge, shear deformation localizes along sharp shear planes resulting in a similar Gaussian slip velocity function where a clear pre-seismic slip is easily detectable. On the other hand, the anhydrite and dolomite mixture, that is characterized larger grain-size and a more distributed deformation, shows a Yoffe slip velocity function having a short acceleration phase and a long deceleration with no pre-seismic creep. In addition, we performed dynamic normal stress steps and document that the slip behavior is strongly controlled by fault zone history for both the lithologies investigated. For overconsolidated fault zones we observe that the transition from stable to unstable behavior is expanded, with slow slip events observed well below the predicted threshold of k kc. By stepping down the normal stress we also document fast and slow stick slip on the same fault patch, however the typical and distinct evolution of slip velocity for quartz and anhydrite/dolomite mixture is maintained. Our results suggest that minor changes in fault loading stiffness, i.e. kc and k, and fault fabric, result in dramatic changes in the mode of fault slip. As applied to tectonic faults, our results suggest that a single fault segment can experience a spectrum of fault slip behaviour depending on the evolution of fault rock frictional properties and elastic conditions of the loading system.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T14B..01S
- Keywords:
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- 3902 Creep and deformation;
- MINERAL PHYSICSDE: 7215 Earthquake source observations;
- SEISMOLOGYDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICSDE: 8163 Rheology and friction of fault zones;
- TECTONOPHYSICS