North Bismarck Plate
The North Bismarck Plate is a small tectonic plate located in the Bismarck Sea off the northeast coast of New Guinea. It is currently regarded as a relic or inactive plate by most.

Tectonics
The plate contains most of the Melanesian arc volcanoes, related to current and historic arc volcanism, except those of New Britain which are on the active South Bismarck Plate.

To the north it has collided with the Pacific Plate and the Caroline Plate, part of the western part is subducting under other active plates in New Guinea, and it is separated from the South Bismarck Plate by a divergent boundary called the Bismarck Seismic Sea Lineation (BSSL). The BSSL is a very seismically active area but the assigned shallow earthquakes tend to be less than magnitude 7.  The plate is moving westerly along with the Pacific Plate.    Between the plate and the Caroline Plate is the Manus Trench and between the plate and the Pacific plate is the Kilinailau Trench. Neither trench has good evidence for current subduction activity but were certainly historically active. There are a few shallow low intensity earthquakes to the south/south west of these trenches on a line of the old arc that extends from the smaller northern Admiralty Islands in the west through to Mussau Island and beyond.

See also
List of earthquakes in Papua New Guinea

References

Tectonic plates
Geology of the Pacific Ocean