Japan Geoscience Union Meeting 2015

Presentation information


Symbol S (Solid Earth Sciences) » S-CG Complex & General

[S-CG59] Rheology, fracture and friction in Earth and planetary sciences

Thu. May 28, 2015 9:00 AM - 10:45 AM 106 (1F)

Convener:*Osamu Kuwano(Japan Agency for Marin-Earth Science and Technology), Tomohiro Ohuchi(Geodynamics Research Center, Ehime University), Ichiko Shimizu(Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo), Hidemi Ishibashi(Graduate School of Science, Shizuoka University), Chair:Hidemi Ishibashi(Graduate School of Science, Shizuoka University), Osamu Kuwano(Japan Agency for Marin-Earth Science and Technology)

9:15 AM - 9:30 AM

[SCG59-07] Effect of liquid viscosity on the shaking condition required for the granular medium fluidization

*Ikuro SUMITA1, Nao YASUDA1 (1.Graduate School of Natural Science & Technology, Kanazawa University)

Keywords:earthquakes, liquefaction, fluidization, magma, triggered eruption, shaking experiments

A liquid-immersed two-layered size-graded granular medium, where the upper layer forms a permeability barrier against the upward percolating liquid, is shaken vertically. A gravitational instability occurs above a critical acceleration (½c) and its amplitude grows. We have previously reported the results of experiments for the water-immersed case (Yasuda & Sumita, 2014). Here we proceed to study the viscosity dependence by conducting experiments for the case in which the liquid is more viscous such that the Stokes velocity is smaller by a factor of 17, and shake it for a corresponding longer time span. We vary the acceleration and frequency of the shaking by 2 and 3 orders of magnitude, respectively, and find that fluidization occurs most efficiently at a frequency band centered around 100 Hz. Importantly, the high viscosity (HV) case has a smaller ½c. In addition the instability of the HV case has a shorter wavelength, and when scaled using the Stokes velocity, the growth rate is faster. The critical acceleration becoming minimum at 100 Hz can be interpreted as follows. For a flame structure to form, a sufficient amount of liquid should accumulate at the 2-layer boundary. A combined condition of energy and jerk of shaking exceeding their critical values, can explain this frequency dependence. A smaller critical acceleration for the HV case can be interpreted as a result of viscous lubrication. To confirm this, we conducted shear stress controlled fluidization experiments of the jammed particles using a rheometer. We indeed find that the fluidization occurs under a smaller shear stress for the HV case. Our experimental situation in which the gravitational instability occurs can be approximated as a thin low density, low viscosity layer underlying a thick high density, high viscosity (with a viscosity which is × ε that of the low viscosity layer) layer. For this situation, linear stability analysis for viscous fluids indicate that the wavelength (λ) scales as λ ∝ ε1/3. Our experimental results suggest that ε becomes smaller for HV case such that λ becomes shorter. A smaller ε value for HV case is consistent with our result indicating that fluidization occurs under a smaller acceleration.
Our experiments indicate that if shaken for a sufficiently long time, fluidization of the HV case occurs under a smaller acceleration because of viscous lubrication. This implies that fluidization of magma is more susceptible to fluidization than the water-saturated case. This may be relevant to liquefaction of magma and earthquake triggering of volcanic eruption.
Yasuda, N., Sumita, I. 2014, Shaking conditions required for flame structure formation in a water-immersed granular medium, Progress in Earth and Planetary Science, 1:13.