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Abundant heterogeneity has been documented on faults in nature across a wide range of length scales, including structural, mineralogical, and roughness variations. The role of complex heterogeneity on fault mechanics and frictional stability is not well established, and experiments investigating heterogeneity have typically incorporated a single source of heterogeneity. Here, we conduct rock friction experiments on rough, bimaterial faults that are creeping, or steadily sliding, to explore the role of lithological heterogeneity on fault mechanics and stability. When strong asperities juxtapose weak gouge, stable sliding occurs with a low friction coefficient, µ. Encounters of strong diabase asperities on talc gouge lined faults initiate dramatic increases in µ and transitions to unstable sliding characterized by frequent stick-slip events (StSE). Seismic moments and stress drops of StSE decrease with increasing asperity abundance. Stress is concentrated at asperities during encounters, increasing with decreasing asperity abundance and leading to extensive mechanical damage. Interactions between strong, velocity weakening asperities provide a model to explain the nucleation of seismic and aseismic slip events on nominally stable, creeping faults.
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The stability of frictional sliding on dip-slip and finite length faults
SUMMARY This paper examines the linear stability of sliding on faults embedded in a 2-D elastic medium that obey rate and state friction and have a finite length and/or are near a traction-free surface. Results are obtained using a numerical technique that allows for analysis of systems with geometrical complexity and heterogeneous material properties; however only systems with homogeneous frictional and material properties are examined. Some analytical results are also obtained for the special case of a fault that is parallel to a traction-free surface. For velocity-weakening faults with finite length, there is a critical fault length $$L^{*}$$ for unstable sliding that is analogous to the critical wavelength $$h^{*}$$ that is usually derived from infinite fault systems. Faults longer than $$L^{*}$$ are linearly unstable to perturbations of any length. On vertical strike-slip faults or faults in a full-space $$L^{*} \approx h^{*}/e$$, where e is Euler’s number. For dip-slip faults near a traction-free surface $$L^{*} \le h^{*}/e$$ and is a function of dip angle $$\beta$$, burial depth d of the fault’s up-dip edge and friction coefficient. In particular, $$L^{*}$$ is at least an order of magnitude smaller than $$h^{*}$$ on shallowly dipping ($$\beta < 10^\circ$$) faults that intersect the traction-free surface. Additionally, $$L^{*} \approx h^{*}/e$$ on dip-slip faults with burial depths $$d \ge h^{*}$$. For sliding systems that can be treated as a thin layer, such as landslides, glaciers or ice streams, $$L^{*} = h^{*}/2$$. Finally, conditions are established for unstable sliding on infinitely-long, velocity-strengthening faults that are parallel to a traction-free surface.
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- Award ID(s):
- 2245540
- PAR ID:
- 10575938
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Geophysical Journal International
- Volume:
- 241
- Issue:
- 2
- ISSN:
- 0956-540X
- Format(s):
- Medium: X Size: p. 826-839
- Size(s):
- p. 826-839
- Sponsoring Org:
- National Science Foundation
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