Evolution of Fault Surface Topography and Structure: Field Measurements, Experimental Results and Model Predictions
Abstract
Geometrical irregularities along faults drive stress heterogeneities that affect the onset of seismic rupture and the ensuing slip dynamics. Field measurements of fault surface topography demonstrate that on-going slip tends to smooth the fault surface parallel to the slip direction. The rate of smoothing is however gradual and decreases with the slip amount. As surface evolution is associated with shear and wear, we measured the width of the fault core with respect to the surface roughness in a single fault zone and found a positive correlation between fault surface amplitudes and fault core width. Measurements of fault core width as function of slip displacement in a few fault branches show that the core width increases with slip amount.
To test how slip surfaces evolve we measured in a series of direct shear laboratory experiments the topographical variations of initially mated and interlocked rough fractures as function of slip distance, normal stress and shear rate. Surfaces were first sheared under constant normal stress of 2 MPa and sliding velocity of 0.05 mm/s, with different target displacements (≤15 mm). We found that shearing smooths the initial surface roughness at all measurement scales. We then measured the roughness evolution as a function of the normal stress for a constant slip target of 10 mm and found that increasing normal stress is associated with surfaces roughening. In the last phase, roughness evolution was measured as a function of slip rate and we found that the final roughness increases moderately with increasing slip velocity. We further study the evolution of slip surfaces roughness and fault-core widths using the framework of a damage-breakage rheological model. The model utilizes a fault structure accommodating wear in a centimeter-scale weak fault core that separates two blocks with damage level decreases smoothly from the core. Our simulations demonstrate that wear process is affected by the initial heterogeneity generated by fault roughness or by initial strength variations. During rupture, wear production is higher along strong patches (barriers). For a given set of boundary conditions, high initial heterogeneity as parameterized by roughness amplitudes or by strength variations results in both a decrease of slip amount and wear production in a rupture event.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.T52C0055S