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Origin and evolution of a splay fault in the Nankai accretionary wedge


Subduction zones are often characterized by wedge-shaped sedimentary complexes—called accretionary prisms—that form when sediments are scraped off the subducting plate and added to the overriding plate. Large, landward-dipping thrust faults can cut through such a prism: these faults, known as ‘megasplay faults’1,2, originate near the top of the subducting plate and terminate at the shallow, landward edge of the prism1,3,4,5,6. Megasplay faults have been the subject of numerous geological and geophysical studies4,5,6,7,8,9,10,11,12,13,14,15, but their initiation and evolution through time remains poorly constrained. Here we combine seismic reflection data from the Nankai accretionary wedge with geological data collected by the Integrated Ocean Drilling Program (IODP) and find that the splay fault cutting this wedge initiated 1.95 Million years (Myr) ago in the lower part of the prism as an out-of-sequence thrust (OOST). After an initial phase of high activity, the movement along the fault slowed down, but uplift and reactivation of the fault resumed about 1.55 Myr ago. The alternating periods of high and low activity along the splay fault that we document hint at episodic changes in the mechanical stability of accretionary prisms.

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Figure 1: Geological setting of the Nankai accretionary wedge.
Figure 2: Data compilation across the shallow megasplay system.
Figure 3: IODP Sites C0004 and C0008; core data.
Figure 4: Summary diagram showing the splay-fault origin and evolution in the Nankai accretionary wedge.


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This research used samples and data provided by the Integrated Ocean Drilling Program (IODP). This work was supported by fellowship grants from the Swiss National Science Foundation (Grant No PBEZ2-118865) and the DFG-Research Centre/Cluster of Excellence ‘The Ocean in the Earth System’ (to M.S.), the US National Science Foundation to the University of Hawaii (G.M.) and the Japanese Ministry of Education, Culture, Science, Sports, and Technology to JAMSTEC.

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M.S., paper writing, lithostratigraphy, data integration, conceptual model; G.M., paper writing, seismic stratigraphy, conceptual model, project planning; G.K., E.J.S., project planning, data integration, J.-O.P., seismic data processing, conceptual model; A.J.K., S.L., conceptual model; Y.K., X.Z., magnetostratigraphy, X.S., biostratigraphy, M.B.U., lithostratigraphy, mineralogy, data integration.

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Correspondence to Michael Strasser.

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Strasser, M., Moore, G., Kimura, G. et al. Origin and evolution of a splay fault in the Nankai accretionary wedge. Nature Geosci 2, 648–652 (2009).

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