Structural profiles in the New Britain / New Ireland region

Abstract

Seismic interpretations along lines of shots and stations in the New Britain/New Ireland region have revealed structural detail in this tectonically complex region. When correlated with marine and land gravity measurements, they indicate a comparatively uniform crust 18 km thick in the eastern Bismarck Sea, thickening to between 30 and 40 km approximately under New Britain and New Ireland. The interpretations indicate crustal thinning of the order of 8 km under the gravity high of central New Britain, and it is suggested that this is upwarping due to northsouth compressional forces. The gravity data indicate that a similar structure could apply to other islands in the Solomon chain. Shear forces seem to dominate the geological structure in the region of the Gazelle Peninsula and southern New Ireland, and the 30 km thick crust there contrasts sharply with an 18 km Bismarck Sea crust along the west coast of the Peninsula. The crustal thickness under New Ireland is the same as that under the islands to the east. The seismicity of the region indicates a multiple junction of crustal plates in the Rabaul area, and the structural characteristics are predominantly a result of a lithospheric subduction zone under New Britain and a multiple shear zone extending across the Bismarck Sea.