Boso Triple Junction

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Tectonic plates under Japan RedDisc.svgBoso Triple Junction

Boso Triple Junction is a triple junction off the coast of Japan; it is the only example of a Triple Trench Junction (Trench, Trench, Trench) on the Earth. It is the meeting point of the North American Plate (represented by the Okhotsk subplate) to the north, the Pacific Plate to the east and the Philippine Sea Plate to the south.

Name origin[edit]

It is named the Boso Triple Junction after the Boso peninsula.


It is formed from the junction of the Izu-Bonin-Mariana Arc where the Izu-Bonin Trench meets with the Japan Trench and the Sagami Trench.


Tokyo is some 300 km from the Boso triple junction, and is subject to quakes and tsunamis generated from slips along this junction. Furthermore, there is a large populated region along the coast of the main island that would also be subject to damage. This junction likely has the highest associated insurance risk in the world, due to proximity to extensive urban development.

The 2011 Tōhoku earthquake and tsunami were generated along the Japan trench well to the north of the junction, and did not involve the other trenches, although quakes which may be aftershocks have been observed there.