Oceanic plate diving beneath continental crust — slab rollback, megathrust, arc volcanism
Occur at the plate interface. The 2011 Tohoku M9.0 ruptured ~500 km of the Japan Trench. Recurrence: hundreds to thousands of years. Slab age & rate control coupling.
As dense old slab sinks, the trench migrates oceanward, stretching the overriding plate and forming back-arc basins (e.g., Mariana Trough).
Sediments scraped off the downgoing slab pile up in a fold-and-thrust belt. Subduction erosion can destroy it (e.g., Chile).
Fluids released from the slab (~100 km depth) lower mantle melting point. Magma rises to form volcanic arcs 100–200 km from the trench.