[S-CG45] Science of slow-to-fast earthquakes

[SCG45-26] Thermal regime and slab dehydration beneath the Izu-Bonin arc: Implications for fast and slow subduction earthquake

*Weiling Zhu^1,2、Yingfeng Ji^1,2、Shoichi Yoshioka^3,4 (1.State Key Laboratory of Tibetan Plateau Earth System, Environment and Resources (TPESER), Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China、2.University of Chinese Academy of Sciences, Beijing 100049, China、3.Research Center for Urban Safety and Security, Kobe University, Rokkodai-cho 1-1, Nada ward, Kobe 657-8501, Japan、4.Department of Planetology, Graduate School of Science, Kobe University, Rokkodai-cho 1-1, Nada ward, Kobe 657-8501, Japan)

キーワード：Izu-Bonin, Thermal regime, Slab dehydration, 3D model

The transition from cold forearc to hot arc is considered fundamental to subduction dynamics. However, the range and depth of the cold nose changing significantly along the strike are difficult to constrain. By incorporating the three-dimensional high-resolution slab topography and MORVEL plate motion field to constrain thermomechanical modeling, we estimate the 3-D subduction thermal state, petrological metamorphism, and slab dehydration in Izu-Bonin. The multilayered hydrothermal regime gradually transitions from cold to less cold forearc, associated with a large-scale subduction dewatering process varying along the strike. The dehydration embrittlement resulting from eclogitization and harzburgitization influences the occurrence of fast to slow earthquakes on megathrusts. The depth of the cold nose and slab-mantle decoupling is widely believed to extend to sub-arc depths of 80-100 km. However, the observations and modeling in this study from surface heat flow and interface seismicity evidence support that the depth of the cold nose is constrained to a depth of approximately 60 km between the arc and the Moho-depth plate interface with a variation in depth along the arc. The lowered temperature and delay of rock harzburgitization in the cold center of the subducted plate at depth contribute to the occurrence of deep earthquakes below the hot backarc interface. For the first time, this study estimates the thermal state and slab dehydration regime for a deep portion of the incoming plate where deep (>200 km) M>5 earthquakes usually occur with temperatures <1000°C deep within the subducted lithosphere and slab dehydration rates varying at approximately >0.02 wt%/km.