Mud volcanism and diapirism along the Japan Trench axis: evidence for a complex earthquake plumbing system on the down-going plate

Mud volcanoes occur in a variety of geodynamic settings, and are common in subduction zones, usually within the accretionary prism. Although mud volcanism occurs along the Ryukyu Trench in southern Japan, no such activity has been documented along the Japan Trench. Sub-bottom profile data from International Ocean Discovery Program Expedition 386 show acoustically anomalous features in the basin-fill stratigraphy consistent with mud diapirism and mud volcanism along the Japan Trench. Unusually these features occur in basins along the trench axis itself, and not primarily as part of the accretionary complex. We present evidence for diapirism along ∼600 km of the Japan Trench and for mud volcanoes in the central and northern part of the trench. Mud diapirism and nearby igneous volcanic activity shows close spatial relationships to flexural faults on the down-going plate, which may provide the plumbing system for mobile muds to reach the surface.