Tectonic Controls on the Subsidence of the Kanto Basin of Japan: An Integrated Model of Three Sided Confinement, Forearc Pull Down, and Miocene Weak Zone Inheritance

The Kanto Basin has undergone 1–3 km of subsidence throughout the Quaternary, despite being situated within an intense compressional stress field—an exceptionally rare tectonic phenomenon worldwide. Building upon the dynamic flattening model proposed in the previous study “Dynamic Flattening of the Kanto Basin”, this paper presents an integrated tectonic framework that explains the subsidence structure itself. The upper plate beneath the Kanto region is confined from the south, north, and west, severely restricting horizontal shortening and lateral flow. Under this mechanically isolated condition, the rapid subduction of the Pacific Plate induces forearc pull‑down, tilting the upper plate obliquely downward. The subsidence axis is geometrically fixed by a Miocene half‑graben structure formed during the opening of the Japan Sea. This integrated model provides a coherent explanation for features that have been difficult to interpret using conventional models, including the eccentric subsidence axis, east–west asymmetry, concentration of active faults on the western margin, persistence of Tokyo Bay, absence of alluvial fans, and the anomalous flatness of the Kanto Plain.