17:15 〜 19:15
[SSS10-P25] 東北沈み込み帯アウターライズ域から採取された堆積物試料の摩擦特性及び透水性への続成作用の影響に関する実験的研究
キーワード：続成作用、スロー地震、摩擦特性、岩石変形
Slow earthquakes and earthquakes occur along the plate boundary of the Tohoku subduction zone. The plate boundary is thought to be composed of subducting sediments enriched in silica and clay minerals. Subduction progressively induces diagenesis in sediments at plate boundaries, leading to dehydration and lithification. Active dehydration of subducting sediments occurs at depths corresponding to the seismogenic zones of both slow earthquakes and earthquakes. Therefore, diagenesis of incoming sediments can significantly influence the mechanical properties of faults, potentially affecting the fault slip movement of plate boundary faults.
The friction experiments on sediments under hydrothermal conditions were performed using a gas-medium, high pressure-temperature triaxial deformation apparatus at Hiroshima University. The samples were collected from the outer-rise region of the Tohoku subduction zone, meaning that this sample has the potential to become a material composing the plate boundary fault at the seismogenic zone in a subduction zone in the future. Prior to the friction experiment, we conducted hydrothermal hot-press experiments on the incoming sediments to simulate diagenesis at a confining pressure of 150 MPa, a pore fluid pressure of 58 MPa, and temperatures ranging from 20℃ to 230℃, and running (cooking) durations of 10 minutes, 1 day, 1 week, and 1 month. After simulating diagenesis, friction experiments with velocity steps were conducted to obtain friction parameters of the rate- and state- dependent friction law.
During cooking, a logarithmic shortening of the sample thickness was observed. This indicates that time-dependent compaction and possibly reaction occurred during experiments. Friction coefficient of sediments from the Tohoku outer rise increased with increasing cooking time and temperature. The value of (a - b) decreased with temperature and with time. Velocity weakening (i.e., negative (a-b) value) was observed when the sample was heated at 100℃ for a week and at 150 ℃ for 10 minutes and 1 day. This condition corresponds to the shallow part of the seismogenic zone. These results indicate that sediments tend to transition from velocity-strengthening to velocity-weakening behavior as diagenesis progresses. This transition from velocity-strengthening to velocity-weakening will take for less than 10 minutes at the temperature above 150℃, for about a week at 100℃, for a few years at 60℃ and for 10 thousand years at 40℃.
These results suggest that long-term, low-temperature diagenetic processes on a geological timescale could induce the spectrum of fault slip behaviors such as steady slip, slow earthquakes and earthquakes
The friction experiments on sediments under hydrothermal conditions were performed using a gas-medium, high pressure-temperature triaxial deformation apparatus at Hiroshima University. The samples were collected from the outer-rise region of the Tohoku subduction zone, meaning that this sample has the potential to become a material composing the plate boundary fault at the seismogenic zone in a subduction zone in the future. Prior to the friction experiment, we conducted hydrothermal hot-press experiments on the incoming sediments to simulate diagenesis at a confining pressure of 150 MPa, a pore fluid pressure of 58 MPa, and temperatures ranging from 20℃ to 230℃, and running (cooking) durations of 10 minutes, 1 day, 1 week, and 1 month. After simulating diagenesis, friction experiments with velocity steps were conducted to obtain friction parameters of the rate- and state- dependent friction law.
During cooking, a logarithmic shortening of the sample thickness was observed. This indicates that time-dependent compaction and possibly reaction occurred during experiments. Friction coefficient of sediments from the Tohoku outer rise increased with increasing cooking time and temperature. The value of (a - b) decreased with temperature and with time. Velocity weakening (i.e., negative (a-b) value) was observed when the sample was heated at 100℃ for a week and at 150 ℃ for 10 minutes and 1 day. This condition corresponds to the shallow part of the seismogenic zone. These results indicate that sediments tend to transition from velocity-strengthening to velocity-weakening behavior as diagenesis progresses. This transition from velocity-strengthening to velocity-weakening will take for less than 10 minutes at the temperature above 150℃, for about a week at 100℃, for a few years at 60℃ and for 10 thousand years at 40℃.
These results suggest that long-term, low-temperature diagenetic processes on a geological timescale could induce the spectrum of fault slip behaviors such as steady slip, slow earthquakes and earthquakes