[S-CG58] New Developments in fluid-rock Interactions: From Surface to Deep Subduction Zone

[SCG58-12] Surface physico-chemical properties of smectite-rich fault gouges: An example of plate-boundary fault at the Japan Trench

Motoki Kamei¹, *Jun Kameda², Keisuke Nakamoto² (1.Department of Earth and Planetary Sciences, School of Science, Hokkaido University, 2.Earth and Planetary System Science Department of Natural History Sciences, Graduate School of Science, Hokkaido University)

Keywords:Japan Trench, plate boundary fault, smectite

Smectite is one of the major clay minerals that make up shallow crustal faults, and its frictional and other physico-chemical properties such as swelling and cation exchange capacity, have a strong influence on faulting behaviors including seismogenesis (Logan and Rauenzahn 1987; Kameda et al., 2016; Kameda et al., 2019). The plate subduction boundary fault at the Japan Trench, which triggered the 2011 Tohoku-Oki earthquake (Mw 9.0) and generated a huge tsunami, is characterized by smectite concentrations exceeding 60% (Chester et al., 2013; Kameda et al., 2015), suggesting that the above physico-chemical properties of smectite are particularly pronounced in fault processes. For example, experiments have shown that such a high smectite concentrations can locally generate high swelling forces within the fault that are nearly equivalent to the overburden load, which may result in very low fault strength conditions (Kameda et al., 2019). Recent our rheological experiments using the analogue fault materials (smectite-quartz mixture with brine) are revealing that the slip behavior of the relevant fault can be approximated by flow deformation with a viscoplastic fluid (Kameda and Hamada, 2020; Kameda and Hamada, 2022). In general, the rheological properties of clay-water systems strongly depend on the interactions forces between clay particles. Such a force is described within the framework of DLVO (Derjaguin and Landau, Verwey and Overbeek) theory, which consists of electrostatic repulsive forces and van der Waals attraction between clay particles. This framework, although classical, has been successfully applied to evaluate the stability of dispersion systems and their rheological parameters such as yield stress and viscosity (e.g., Montoro and Francisca, 2019).
In this study, we conducted zeta potential measurements of the recovered fault gouges from the Tohoku fault zone by electrophoresis using solutions that simulate extracted pore fluids. We also determined surface free-energy of particles by contact angles measurements of three probe liquids (diiodomethane, water, and formamide) of known surface-tension components on dry pellets. The interaction forces between the particles were then assessed by using extended form of DLVO theory, which also includes acid-base contribution (i.e., electron donor-acceptor interactions) in addition to the other forces described above (Van Oss, 1994). Based on the results, we discuss the importance of surface physicochemical properties of clay particles on the slip behavior of the relevant fault.

Reference Logan and Rauenzahn, 1987, Tectonophys 87–108. Kameda et al., 2016 GRL 43. Kameda et al., 2019 EPS 71:131. Chester et al., 2013, Science 1208–1211. Kameda et al., 2015 Geology 155–158. Kameda and Hamada, 2020 GRL 47. Kameda and Hamada, 2022 PRR 4. Montoro and Francisca, 2019, ACS, 178. Van Oss et al., 1988 Chem Rev 88.