Abstract
Combined knowledge on the magnitude as well as the orientation of paleo-stress is usually not given. Based on drilling investigations and laboratory experiments, we are able to provide both, constraints on paleo-stress magnitude as well as orientation in the shallow part of the Nankai accretionary wedge at Sites C0001 and C0002 of the Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE). Slip data of core-scale faults indicate multiple paleo-stress geometries, including normal, strike-slip, and reverse faulting regimes. Combining new and previously obtained results from triaxial compressional tests that constrain internal friction angles at critical state with the paleo-stress inversion results, we examine paleo-stress magnitudes for each stress state at each site. We observe that the paleo-stress magnitude for the normal faulting regime is smaller than that for the reverse faulting regime, although the paleo-stress magnitude for Site C0002 is not well-constrained. The change in stress magnitude may reflect changing horizontal tectonic stresses transmitted to the accretionary wedge from changing friction conditions along the subduction plate interface and in turn may have implications for the evolution of the accretionary wedge and/or the seismic cycle.
Highlights
The state of stress in a subduction zone system exerts important controls on accretionary wedge architecture, intra-wedge fault development, and seismic behaviors along the megathrust plate boundary and splay faults (e.g., Wang and Hu 2006;, Lin et al 2013; Schumann et al 2014a)
The contemporary stress state within the shallow portion of an accretionary prism can be obtained by borehole observations (Chang et al 2010; Zoback et al 2003) or anelastic strain recovery (ASR) measurements on core
At the Nankai trough, recent studies have integrated borehole and ASR results with constraints on material properties to conclude that the stress state for the shallow portion of the wedge is consistent with a normal faulting regime with vertical maximum principal stress (e.g., Byrne et al 2009; Lin et al 2015; Kitajima et al 2017; Oohashi et al 2017)
Summary
The state of stress in a subduction zone system exerts important controls on accretionary wedge architecture, intra-wedge fault development, and seismic behaviors along the megathrust plate boundary and splay faults (e.g., Wang and Hu 2006;, Lin et al 2013; Schumann et al 2014a). At the Nankai trough, recent studies have integrated borehole and ASR results with constraints on material properties to conclude that the stress state for the shallow portion of the wedge is consistent with a normal faulting regime with vertical maximum principal stress (e.g., Byrne et al 2009; Lin et al 2015; Kitajima et al 2017; Oohashi et al 2017).
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