[S-SS07] Fault Rheology and Earthquake Physics

[SSS07-P05] Stick-slip behavior of San Carlos olivine aggregates at the brittle-plastic transition and the strength profile of the oceanic mantle

*Keishi Okazaki¹ (1.Japan Agency for Marine-Earth Science and Technology)

Keywords:Peridotite, Outer rise earthquake, Friction, Fracture, Olivine

Rheology of olivine in the mantle peridotites largely controls the overall dynamics of the plate tectonics. While various flow laws of olivine aggregates have been reported/proposed at various conditions, deformation behavior of olivine aggregates at the brittle-plastic transition, which could also control the outer-rise seismicity, is poorly understood. In this presentation, I will talk on the deformation behavior of olivine aggregates at pressure-temperature conditions of the base of the seismogenic zone around outer-rise regions around the Japan trench. Audible and violent stick-slips followed by acoustic emissions were observed even at the temperature of 800 degC. However, the nominal friction coefficient at this condition is ~0.4, which value is significantly lower than that expected from the Byerlee’s friction law (i.e., 0.6–0.85). Comparison between mechanical data and microstructural observation indicates that the strain was localized along R1-shear connected to Y- (or B-) shear with some contents of crystal-plastic deformation. These weak but seismic deformation could be dominant in the oceanic lithosphere. Initial results on high coffining and pore fluid pressures deformation experiments of olivine aggregates under drained condition will also be talked.