Fig. 9

Conceptual rheological model of the Japan trench at Miyagi. a The down-going Pacific slab intersects different terranes of the Japanese arc at various dip angles, introducing rheological and morphological gradients that shape the seismic super-cycle. The megathrust occupies the brittle regime of the plate interface, stopping down-dip at the brittle–ductile transition. In the mantle wedge, the coupling between the two plates is permanent, entraining corner flow below the volcanic arc. Fluids enter the mantle wedge underneath Honshu from the Pacific lithosphere and the Sea of Japan asthenosphere. b The megathrust is segmented into the weak frontal prism and the forearc upper crust, the forearc basement, the mantle-wedge corner, cold nose, and upper mantle. The segments are named after the hanging wall block that they underlie. The mega-splay fault delineates the active frontal prism. Large Mw\(\sim\)7 earthquakes are mostly confined in a single segment, with rupture nucleation close to structural boundaries. Giant Mw\(\sim\)9 ruptures break the entire offshore section, reaching the trench. Megathrust segments in the upper mantle exhibit stable creep. The cross-section area in b) is shown as a dashed box in the top panel