Where it is
The Solomon Sea Plate covers about 129,000 km² under the Solomon Sea, between the Papuan Peninsula, New Britain and Bougainville. It carries no land. Its earthquakes are recorded under the names of the nearest towns in Papua New Guinea, such as Kokopo and Panguna.
The plate is a leftover piece of older ocean floor trapped between converging arcs. Geologists treat it as a separate plate because it is bounded on all sides by trenches that sink at very different speeds, so it cannot belong to any of its neighbors.
A plate with only convergent edges
Every boundary of the Solomon Sea Plate is convergent, which is rare. Along the north, it sinks beneath the South Bismarck Plate at the New Britain Trench. Relative speeds there average about 11.3 cm/yr and reach about 15.8 cm/yr, which places the New Britain Trench among the fastest subduction zones in the PB2002 model.
On the southwest side, the plate meets the Woodlark Plate along 899 km of the Trobriand Trough. Here convergence is slow, about 1.3 cm/yr, and part of the boundary is transform faulting. At the eastern corner, where the New Britain Trench bends toward Bougainville, the plate also sinks beneath the North Bismarck Plate at about 8.2 cm/yr and beneath the Pacific Plate at about 9.1 cm/yr.
Earthquakes
The dataset lists 17 earthquakes of magnitude 6.5 or larger on the plate since 1900, none reaching magnitude 8. The largest was an M7.5 quake in August 1972, about 199 km south-southeast of Kokopo. Others include an M7.2 quake in 1974 and an M7.1 quake in May 2015, both southwest of Panguna on Bougainville. Most of these quakes were shallow, at depths under 50 km.
The biggest earthquakes linked to this plate actually happen just outside its borders. As the Solomon Sea slab sinks under New Britain and New Ireland, it breaks in great quakes that the dataset assigns to the overriding plates, such as the 1971 New Britain (M8.0) and Bougainville (M8.1) earthquakes.
The plate has no volcanoes of its own. Magma forms only after the slab sinks deep beneath its neighbors, so the volcanoes it feeds, such as Ulawun and Rabaul on New Britain, sit on the South Bismarck Plate.