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doi:10.2204/iodp.proc.314315316.102.2009

Conclusions

Our 3-D seismic reflection data set images several key features of the NanTroSEIZE Kumano transect that are relevant to the drilling results reported in this volume:

• The frontal thrust region is anomalous compared to other parts of the Nankai Trough in that the thrust is a shallow-dipping detachment that extends >10 km landward, whereas the frontal thrusts in other parts of the Nankai prism dip ~30° and extend no more than 1 km landward. Near the toe of the prism is an OOST that has recently overridden the frontal block.
• At the frontal part of the megasplay system, our 3-D data show that the underlying accretionary prism thrusts have oblique slip that generated lateral (or oblique) ramp hanging wall anticlines. The oblique ramp structures have been truncated by the megasplay, which has overridden at least 1250 m of young slope sediments. The tip of the megasplay fault is a complex anastomosing series of thrusts that strongly deform the underlying slope sediments. Northwest-striking normal faults cut the slope sediment section beneath and in front of the megasplay fault.

Key interpretations of seismic reflection data across the forearc basin are (1) landward tilting of the basin section, (2) hemipelagic strata below the main basin fill that drape an older unit and are interpreted to be slope/​slope basin strata, and (3) older accretionary prism material below the forearc/​slope sediments.

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