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

• Published in: Nature geoscience Vol. 2; no. 9; pp. 648 - 652
• Main Authors: Strasser, Michael, Moore, Gregory F., Kimura, Gaku, Kitamura, Yujin, Kopf, Achim J., Lallemant, Siegfried, Park, Jin-Oh, Screaton, Elizabeth J., Su, Xin, Underwood, Michael B., Zhao, Xixi
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.09.2009; Nature Publishing Group
• Subjects: Earth and Environmental Science; Earth Sciences; Earth System Sciences; Fault lines; Geochemistry; Geology; Geophysical studies; Geophysics/Geodesy; letter
• ISSN: 1752-0894; 1752-0908
• DOI: 10.1038/ngeo609

The sedimentary wedge in the Nankai Trough off the coast of Japan is cut by a landward-dipping thrust fault, which is an important plate boundary structure in this region. Geological and seismic reflection data indicate that the fault initiated ∼1.95 million years ago and underwent uplift and reactivation ∼1.55 million years ago. 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 prism 1 , 3 , 4 , 5 , 6 . Megasplay faults have been the subject of numerous geological and geophysical studies 4 , 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.