Tectonic regime of the southern Kurile Trench as revealed by multichannel seismic lines

Abstract

The analysis of the two multichannel seismic reflection records P-855 and P-856 reveals the complexity of the tectonic structure of the Kurile margin. The absence of trench fill and the relatively constant thickness of the subducted sediments on top of the oceanic basement shows that little or no accretion is occurring at present. The lower slope is characterized by active thrusting within a small accretionary prism. The toe of the middle slope is a more consolidated unit that constitutes an efficient buttress. A piggy back basin, possibly filled by sediments that have drifted down slope, has formed on top of this unit. A narrow high marks the transition to the edge of the continental terrace. Furthermore, the upper slope reveals an unconformity marking the top of the basement. The similarity of this unconformity and its sedimentary cover with the well documented data acquired around DSDP Legs 56–57 suggests that northern Japan and the southern Kurile forearcs may have experienced a similar Cenozoic vertical history.