Polarity reversal in the Solomon Islands arc

Abstract

McKenzie¹ proposed that the direction of subduction beneath an island arc will reverse following arc–continent collision. Dewey and Bird² suggested that such an arc polarity reversal occurred in northern New Guinea; Johnson and Molnar³, however, proposed two alternative models of plate convergence that could explain the observed seismicity. We present here a spatial seismicity study of the Solomon Islands region which has revealed the existence of two juxtaposed Wadati–Benioff (W–B) zones of opposite polarity. Shallow and intermediate foci define a north-east-dipping W–B zone associated with active subduction along the New Britain and San Cristobal trenches and a south-west-dipping W–B zone associated with the inactive North Solomon trench (NST). These data provide the first direct seismic evidence of a reversal in subduction polarity at an island arc.