Fault Mechanics Webinar Friday March 17: Exploring flash heating coupled with mm-scale contact evolution in granite

FRIDAY MARCH 17, 2023 @ 1P PDT

Exploring flash heating coupled with mm-scale contact evolution in granite

Monica Barbery, Brown University

Flash-weakening models show good agreement with the total magnitude of weakening observed in high-velocity rock friction experiments, however deviations from model predictions during the acceleration and deceleration phases remain unresolved. Here, I present recent work on Westerly granite using a high-speed biaxial apparatus outfitted with a high-speed infrared camera. We use unique sliding surface geometries to control mm-scale life-times and rest-times and to inform 1-D thermal models. We compare model predictions with measured surface temperatures to constrain the evolution of local normal stress at the mm-scale and incorporate this evolution into a flash heating model that considers weakening at both the µm- and mm-scale. [more info] [register]

FRIDAY MARCH 24, 2023 @ 1P PDT

Hydrothermal friction experiments on simulated basaltic fault gouge and implications for megathrust earthquakes

Hanaya Okuda, University of Tokyo

Nucleation of earthquake slip at the plate boundary fault (décollement) in subduction zones has been widely linked to the frictional properties of subducting sedimentary facies. However, recent seismological and geological observations suggest that the décollement develops in the subducting oceanic crust in the depth range of the seismogenic zone, at least in some cases. To understand the frictional properties of oceanic crustal material and their influence on seismogenesis, we performed hydrothermal friction experiments on simulated fault gouges of altered basalt, at temperatures of 100–550°C. The friction coefficient (μ) lies around 0.6 at most temperature conditions but a low μ down to 0.3 was observed at the highest temperature and lowest velocity condition. The velocity dependence of μ, (a−b), changes with increasing temperature from positive to negative at ∼100°C and from negative to positive at ∼450°C. Compared to gouges derived from sedimentary facies, the altered basalt gouge showed potentially unstable velocity weakening over a wider temperature range. Microstructural observations and microphysical interpretation infer that competition between dilatant granular flow and viscous compaction through pressure-solution creep of albite contributed to the observed transition in (a−b). Alteration of oceanic crust during subduction produces fine grains of albite and chlorite through interactions with interstitial water, leading to reduction in its frictional strength and an increase in its seismogenic potential. Therefore, shear deformation possibly localizes within the altered oceanic crust leading to a larger potential for the nucleation of a megathrust earthquake in the depth range of the seismogenic zone. [more info] [register]