5:15 PM - 7:15 PM
[SSS10-P24] Frictional properties of limestone from seamounts under high temperature and high pressure
Keywords:Friction experiment, Subduction zone, Seamount, Limestone
Earthquakes at a subduction plate interface are considered to occur due to the rupture of asperities. Topographic irregularity of subducted seafloor, such as seamount, is one of the factors influencing asperity formation. Seamounts are thought to generate large earthquakes by increasing the normal stress on the subduction interface (e.g., Cloos, 1992). On the other hand, they are also assumed to act as barriers for rupture propagation (e.g., Kodaira et al., 2000), or may promote creep or slow slip behavior (e.g., Mochizuki et al., 2008). Okuma et al. (2022) reveal that the friction on the surface of seamounts as well as the topographical influence contributes to forming geologically complex structures. Despite these numerous studies on subducting seamounts, systematic friction experiments focusing on subducting seamounts remain insufficient. This study aims to investigate the frictional properties of seamount-derived rocks and their relationship with earthquake generation through the experiments.
We used limestone sample collected from a Jurassic accreted seamount at the Funafuseyama Unit, the Mino Belt in Gifu Prefecture, Japan. Thin-section observations and X-ray diffraction analyses revealed that the limestone sample consists of calcite (98.2 wt%) and quartz (1.8 wt%).
Experiments were conducted using a gas-medium, high-temperature, high-pressure triaxial apparatus at AIST, at a confining pressure of 150 MPa, a pore pressure of 100 MPa, temperatures of 20-200°C, and axial displacement rates of 0.1-100 µm/s. The steady state friction (μss) ranged from 0.70 to 0.80 under all temperature conditions we investigated. The value of friction parameter (a-b) (rate dependence of μss) depend significantly on temperatures: it decreases from positive (0.0023-0.0159) to neutral with increasing temperatures to 100°C, then it becomes negative (-0.0012--0.0041) at temperatures higher than 150°C.
The same trend of (a-b) was also observed in seamount-derived basalt (Sawai et al., 2024 JpGU). This suggests that a seamount may be a site of earthquake nucleation at depths with temperatures of >100°C if limestone or basalt is present on a seamount at the plate boundary. In addition, since limestone has a higher strength (μss: 0.70-0.80) than basalt (μss: 0.39-0.55), basalt is more likely to undergo deformation than limestone when both lithologies coexist.
We used limestone sample collected from a Jurassic accreted seamount at the Funafuseyama Unit, the Mino Belt in Gifu Prefecture, Japan. Thin-section observations and X-ray diffraction analyses revealed that the limestone sample consists of calcite (98.2 wt%) and quartz (1.8 wt%).
Experiments were conducted using a gas-medium, high-temperature, high-pressure triaxial apparatus at AIST, at a confining pressure of 150 MPa, a pore pressure of 100 MPa, temperatures of 20-200°C, and axial displacement rates of 0.1-100 µm/s. The steady state friction (μss) ranged from 0.70 to 0.80 under all temperature conditions we investigated. The value of friction parameter (a-b) (rate dependence of μss) depend significantly on temperatures: it decreases from positive (0.0023-0.0159) to neutral with increasing temperatures to 100°C, then it becomes negative (-0.0012--0.0041) at temperatures higher than 150°C.
The same trend of (a-b) was also observed in seamount-derived basalt (Sawai et al., 2024 JpGU). This suggests that a seamount may be a site of earthquake nucleation at depths with temperatures of >100°C if limestone or basalt is present on a seamount at the plate boundary. In addition, since limestone has a higher strength (μss: 0.70-0.80) than basalt (μss: 0.39-0.55), basalt is more likely to undergo deformation than limestone when both lithologies coexist.