ALBERT

Description: 〈span〉〈div〉Summary〈/div〉The recently evolving crustal deformation monitoring systems detect slow slip events, which are failures that are slower-paced than ordinary earthquakes, in the decollement zone of the shallow part of the plate subduction boundary zone. When the 2011 earthquake off the Pacific coast of Tohoku occurred, the decollement zone became the source of a massive tsunami. Deep-sea scientific drilling of the decollement zone has shown that the surrounding shear zone area is composed of a mixture of smectite and illite. These clay minerals differ in their frictional characteristics. This study proposes a mathematical model using a continuity equation to express the interactions between the solid and liquid phases and an elasto-plastic constitutive relation for the soil skeleton, considering the alteration of smectite to illite. In doing so, the decollement zone is viewed as a problem involving soil/water coupling in a mixture, where the soil skeleton is the solid and the pore water is the liquid. The dehydration of interlayer water in smectite, changes in frictional characteristics resulting from illitization, and changes in dilatancy characteristics are considered in this model. Shear simulations were also conducted, factoring in alteration. The simulation results revealed that the shear strength increased with alteration, and accordingly shear stress increased when the shear deformation is further applied. Since the shear strength increased with alteration, shear deformation was less likely to occur in the decollement zone, and it was considered that the sticking between the plate could be simulated.〈/span〉