Fault & Rock Rheology

Shear experiments on quartz-albite mixtures at simulated mid-to-lower crustal conditions revealed the microphysical mechanisms controlling the brittle-plastic transition. Grain boundary sliding in nano-grain domains governs crustal strength at the transition zone, providing key insights into the strongest part of the crust where large earthquakes nucleate.

High-pressure deformation experiments on germanate olivine triggered phase-transformation faulting from olivine to spinel. The resulting acoustic emissions followed magnitude-frequency distributions consistent with natural deep-focus earthquakes, providing experimental evidence that transformational faulting can produce seismicity analogous to deep earthquakes in subducting slabs.

A split Hopkinson pressure bar system was developed for experimental investigation of dynamic pulverization of rocks at very high strain rates, simulating seismic rupture propagation. This apparatus enables quantitative analysis of fragmentation processes relevant to earthquake source physics.

High-temperature deformation experiments on quartz and granulite under wet conditions revealed transient creep behavior that deviates from steady-state flow laws. These results have important implications for modeling postseismic deformation and understanding the time-dependent rheology of the lower crust and upper mantle.

Deformation experiments demonstrated that metamorphic reactions involving the formation of hydrous phases fundamentally weaken oceanic lithosphere, enabling the initiation of subduction. This reaction-induced rheological weakening provides a critical mechanism for understanding how rigid oceanic plates begin to subduct.

Laboratory studies of unstable slip along simulated fault zones of serpentine and olivine revealed that lower friction coefficients (μ from 0.7 down to 0.5) lead to increasing slow rupture mode. Slow rupture velocities (0.07 to 5.43 m/s) are largely consistent with short-term SSEs observed in nature, suggesting that SSE generation is facilitated by low normal stress and low fault-zone strength.

Pin-on-disk friction experiments on single crystalline quartz revealed velocity weakening from μ~0.6 to 0.4. Raman spectra showed pressure- and strain-induced amorphization of quartz, and FT-IR mapping suggested selective hydration of wear materials. Strained Si-O-Si bridges in amorphous silica may react with water to form silica-gel, leading to significant fault strength reduction during slip.

The effect of lattice preferred orientation on flow strength of quartz aggregates dynamically recrystallized from single crystals was investigated using general shear experiments in a Griggs apparatus at 900°C and 1.5 GPa. All three initial crystal orientations undergo dynamic recrystallization, developing domains with c axes parallel to Y of the strain ellipsoid, indicating geometrical softening of up to an order of magnitude in effective viscosity.