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Data report: tectonic and induced structures in the JFAST core: Expedition 343

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Proceedings of the IODP

Integrated Ocean Drilling Program

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      Abstract

      Structures surrounding the inferred location of the Japan Trench plate boundary decollement define the fault damage zone. We quantify the density of tectonic and induced structures in the damage zone from drill cores collected between 770 and 835 meters below seafloor from Hole C0019E during Integrated Ocean Drilling Program Expedition 343/343T, the Japan Trench Fast Drilling Project (JFAST). Cores contain structures formed by tectonic deformation and structures resulting from drill core recovery and handling. Differentiating between these two origins is essential for structural analyses and interpretation. We defined 10 styles of induced structures that we used to develop a new set of criteria for identifying induced structures in drill cores containing fine-grained sedimentary rocks. These criteria were used to categorize structures according to confidence in a tectonic origin. Our results show structure density (including all fractures, faults, breccias, and phyllosilicate bands) has a maximum adjacent to the decollement. This pattern in structure density is apparent for both exclusively tectonic structures and tectonic and induced structures combined. Local increases in induced structure density mask trends in tectonic structures, demonstrating that detecting trends in spatial variability in structure density is dependent on the recognition of induced structures. Additionally, the tectonic structure density increases where cores contain faults with significant displacements inferred from stratigraphic information, indicating that tectonic structure density can be used to identify secondary faults. We suggest that the criteria for identifying induced structures used in this study could be applied during visual core description in a variety of tectonic settings as a method to collect and assess reliable structural data.

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      Most cited references 29

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      Shallow dynamic overshoot and energetic deep rupture in the 2011 Mw 9.0 Tohoku-Oki earthquake.

      Strong spatial variation of rupture characteristics in the moment magnitude (M(w)) 9.0 Tohoku-Oki megathrust earthquake controlled both the strength of shaking and the size of the tsunami that followed. Finite-source imaging reveals that the rupture consisted of a small initial phase, deep rupture for up to 40 seconds, extensive shallow rupture at 60 to 70 seconds, and continuing deep rupture lasting more than 100 seconds. A combination of a shallow dipping fault and a compliant hanging wall may have enabled large shallow slip near the trench. Normal faulting aftershocks in the area of high slip suggest dynamic overshoot on the fault. Despite prodigious total slip, shallower parts of the rupture weakly radiated at high frequencies, whereas deeper parts of the rupture radiated strongly at high frequencies.
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        Implications for mechanical properties of brittle faults from observations of the Punchbowl fault zone, California

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          The 2011 Tohoku-Oki earthquake: displacement reaching the trench axis.

          We detected and measured coseismic displacement caused by the 11 March 2011 Tohoku-Oki earthquake [moment magnitude (M(W)) 9.0] by using multibeam bathymetric surveys. The difference between bathymetric data acquired before and after the earthquake revealed that the displacement extended out to the axis of the Japan Trench, suggesting that the fault rupture reached the trench axis. The sea floor on the outermost landward area moved about 50 meters horizontally east-southeast and ~10 meters upward. The large horizontal displacement lifted the sea floor by up to 16 meters on the landward slope in addition to the vertical displacement.
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            Author and article information

            Journal
            10.2204/iodp.proc.343343T.2013
            Proceedings of the IODP
            Integrated Ocean Drilling Program
            1930-1014
            04 March 2016
            10.2204/iodp.proc.343343T.204.2016

            This work is licensed under a Creative Commons Attribution 4.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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            Self URI (journal page): http://publications.iodp.org/

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