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Singlechannel seismic-reflection profiles collected acros the convergent plate boundary in the central New Hebrides Arc display structures that can account for the observed absence of a deep geotectonic trench. These structures include (1) the protrusion of the Sanbhlalakula block at the leading edge of the overriding plate, (2) collision of ridges on the downgoing plate with this block, (3) slumping of sediment from the insular wall of the trench, and/or the tectonic displacement of material outward to compensate for adjacent indentation by colliding features, (4) compressive doming of the downgoing plate adjacent to the zone of plate contact, and (5) sediment filling of incipient trenches. The superficial structures indicate that there are three major zones of dominant stress affecting the top of the downgoing plate in this region. North of the North D'Entrecasteaux Ridge and south of latitude 17 S, tensional stress regimes are related to the passive bending of the plate under the weight of the downgoing slab. There is weak coupling between the plates and subduction is mainly controlled by creep. Between the North D'Entrecasteaux Ridge and latitude 17 o S, a compressional stress regime indicates relatively strong coupling between the plates. The highest compressional stresses occur at the Bougainville Spur and probably at the North D'Entrecasteaux Ridge-collision points that can be related to localized shallow asperities in the Benioff zone. The transitions between these regions of contrasting stress regime that occur at latitude 17"s and along the northern flank of the D'Entrecasteaux zone are probably areas of shearing transverse to the trench.