Which plate subducts beneath the Okhotsk plate at the Japan Trench?

At the Japan Trench, the Pacific Plate subducts beneath the Okhotsk Plate.

Subduction occurs when the older, denser oceanic Pacific Plate bends downward and sinks below the Okhotsk microplate, which carries northeastern Japan, including much of Tōhoku and Hokkaido. This descending slab creates the Japan Trench, an approximately 800-km feature running from the Kuril Islands toward the Izu Islands.

The boundary is one of the most seismically active zones on Earth. As the plates converge, stress can accumulate along the locked interface and then release in powerful earthquakes. The best-known example is the magnitude 9.0–9.1 Tōhoku earthquake of 11 March 2011, which generated a devastating tsunami and caused severe damage along Japan’s northeastern coast.

A common source of confusion is the Philippine Sea Plate: it subducts beneath parts of southern Japan and is involved with the Nankai Trough and Izu-Ogasawara system, but it is not the plate descending at the Japan Trench. The Okhotsk Plate itself is sometimes treated as part of the North American Plate in older models, but modern descriptions commonly identify it as a separate microplate.