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Strain decoupling reveals variable seismogenic risk in SE Japan (Nankai Trough)

Van Tuyl, James, Alves, Tiago and Moore, Gregory F. 2015. Strain decoupling reveals variable seismogenic risk in SE Japan (Nankai Trough). Geochemistry Geophysics Geosystems 16 (7) , pp. 2025-2037. 10.1002/2015GC005778

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The determination of in situ stress states is vital in understanding the behavior of faults and subsequent seismogenesis of accretionary prisms. In this paper, a high quality 3D seismic volume is used to map the depth of the extensional-compressional decoupling (ECD) boundary in the accretionary prism of Nankai, with the prior knowledge that strike-slip and compressional stresses occur deeper than 1250 meters below seafloor (mbsf) in the Kumano Basin, changing to extension towards the seafloor. A total of 1108 faults from the accretionary prism are analyzed to estimate paleostresses via fault inversion and slip tendency techniques. A key result is this paper is that the ECD boundary can be used as a proxy to identify active structures on accretionary prisms as its depth depends on: a) local tectonic uplift in areas adjacent to active faults, and b) on the thickness of sediment accumulated above active thrust anticlines. The depth of the ECD boundary ranges from 0 to ∼650 mbsf, being notably shallower than in the Kumano Basin. In Nankai, frontal regions of the imbricate thrust zone, and the megasplay fault zone, reveal the shallower ECD depths and correlate with the regions where faulting is most active. As a corollary, this work confirms that estimates of stress state variability based on the analysis of 3D seismic data are vital to understand the behavior of faults and potential seismogenic regions on convergent margins. This article is protected by copyright. All rights reserved.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Additional Information: Pdf uploaded in accordance with publisher's policy at (accessed 22.05.15).
Publisher: American Geophysical Union.
ISSN: 1525-2027
Date of First Compliant Deposit: 30 March 2016
Date of Acceptance: 13 May 2015
Last Modified: 27 Mar 2020 02:20

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