[S-CG46] Uncovering stress accumulation and fault strengthening of megathrust earthquakes

[SCG46-P11] The Impact of Hydrothermal Circulation on Megathrust Earthquake in Subduction Zones

*Jae Hoon Lee¹, Dongwoo Han², Changyeol Lee¹ (1.Department of Earth System Sciences, Yonsei University, 2.Department of Earth Sciences, University of Oxford)

Keywords:Hydrothermal Circulation, Megathrust Earthquake, Numerical Modeling, Brittle-Ductile Transition, Smectite-Illite Transformation

Numerous studies on subduction zones have focused on the mechanism of megathrust earthquakes occurring along the plate interface between the overlying crust and sinking oceanic plate, directly threatening humane lives and properties. One major factor that constrains the location and magnitude of megathrust earthquakes is the effective coefficient of friction of the plate interface. The coefficient represents the overall characteristics of the plate interface, including the effects of hydrothermal circulation, brittle-ductile transition, and mineral transformation on the friction of the seismogenic zone. However, many previous studies of numerical models suggested very low effective coefficient of friction values without quantitative consideration of the major hydraulic, rheologic, and phase-change phenomena. Therefore, our numerical models implement hydrothermal circulation, brittle-ductile transition, and mineral transformation to estimate the effective coefficient of friction of the plate interface in the Southwest (young and hot) and Northeast Japanese (old and cold) subduction zones. In the models, we vary the effective coefficient of friction and compare the heat flow observed across the forearc region to validate the coefficient. Our model results show that vigorous hydrothermal circulation occurs along the plate interface in Southwest Japan because of the young and hot subducting slab and high permeability of the oceanic crust. The hydrothermal circulation distributes heat along the plate interface and increases the overall temperature, which results in a shallower depth of brittle-ductile transition and smectite-illite transformation. On the other hand, Northeast Japan shows weak hydrothermal circulation occurs along the plate interface because of the old and cold subducting slab and low permeability of the oceanic crust. In this case, heat conduction instead of hydrothermal circulation only transports heat toward the overlying crust, resulting in a deep depth of brittle-ductile transition and smectite-illite transformation. The effective coefficient of friction in the Southwest and Northeast Japan subduction zones is used to estimate the pore pressure along the plate interface, constrained by seismological studies and drilling data. In addition, the calculated thermal structure of the forearc region is expected to unravel the earthquake process at the updip of the seismogenic zone.