Philippine Sea Plate
The Kanto area lies above a complex part of the convergent boundaries between the subducting Pacific and Philippine Sea Plates and the overriding Eurasian and North American Plates. Earthquakes with epicenters in the Kantō region may occur within the Eurasian Plate, at the Eurasian Plate/Philippine Sea Plate interface, within the Philippine Sea Plate, at the Philippine Sea Plate/North American Plate interface (under the Sagami Trough), at the Philippine Sea Plate/Pacific Plate interface (Izu–Bonin–Mariana Arc), or within the Pacific Plate. In addition to this set of major plates it has been suggested that there is also a separate 25 km thick, 100 km wide body, a fragment of Pacific Plate lithosphere.