10:45 AM - 12:15 PM
[SCG45-P47] Structure and phase diagram of model clay in fault zone using molecular dynamics
Keywords:Clay, Fault slip, Structure
The slip behavior of a fault is governed by the frictional resistance of the solid contacting surface. This can be altered when other geomaterials intervene. During the March 2011 Tohoku-Oki earthquake, a large slip in the shallow part of the fault zone caused a huge tsunami. The shallow part of this fault was generally considered as non-seismogenic before. Further drilling investigation shows the fault zone is composed of 60~80% smectite clay (Fulton et al., 2013). The low friction of the weak smectite (mainly montmorillonite) and the rise of pore-water pressure are considered as the main causes of the slip from shear experiment on the fault material (Ujiie et al., 2013). Although some models for the stick-slip behavior have been proposed, the rheology of clay-rich zones are still unclear (Kameda & Hamada 2022). A more detailed study to consider the effect of clay on fault slip is needed.
As clay is the product of chemical weathering of other silicate minerals, its sheet structure and nanometer size is different from common granular particles in the gouge layer. Once dispersed in water, clay particles hydrate and swell. The cation exchange leads to charges on the surface and edges. Therefore, clay particles are sensitive to environmental parameters such as salt concentrations and pH value (Shen & Bourg 2021).While many previous clay studies focus on room temperature and atmosphere pressure, changing salt concentration and clay concentration give the clay-water system a versatile phase diagram (Ruzicka & Zaccarelli 2011). But for studies of earthquake and fault zone, a different range should be specified with higher temperature/ pressure. High salt concentration in the seawater environment (Kameda et al., 2016) and the presence of shear stress should also be taken into account.
In this study, we present a tentative approach to study the phase and structure of clay in molecular dynamics simulation. The detailed atomistic structure of clay mineral is neglected in the Coarse-Grained Molecular Dynamics (Ebrahimi et al., 2014). an individual clay particle is simplified as a rigid ellipsoid with a large aspect ratio. Gay-Berne potential, which is commonly used for liquid crystal, is adopted for clay to present the anisotropy characteristics in both particle shape and interaction. The phase/ structure of the particle system is investigated for a range of temperature and pressure and then compared to the condition in the fault zone.
As clay is the product of chemical weathering of other silicate minerals, its sheet structure and nanometer size is different from common granular particles in the gouge layer. Once dispersed in water, clay particles hydrate and swell. The cation exchange leads to charges on the surface and edges. Therefore, clay particles are sensitive to environmental parameters such as salt concentrations and pH value (Shen & Bourg 2021).While many previous clay studies focus on room temperature and atmosphere pressure, changing salt concentration and clay concentration give the clay-water system a versatile phase diagram (Ruzicka & Zaccarelli 2011). But for studies of earthquake and fault zone, a different range should be specified with higher temperature/ pressure. High salt concentration in the seawater environment (Kameda et al., 2016) and the presence of shear stress should also be taken into account.
In this study, we present a tentative approach to study the phase and structure of clay in molecular dynamics simulation. The detailed atomistic structure of clay mineral is neglected in the Coarse-Grained Molecular Dynamics (Ebrahimi et al., 2014). an individual clay particle is simplified as a rigid ellipsoid with a large aspect ratio. Gay-Berne potential, which is commonly used for liquid crystal, is adopted for clay to present the anisotropy characteristics in both particle shape and interaction. The phase/ structure of the particle system is investigated for a range of temperature and pressure and then compared to the condition in the fault zone.