Modern and ancient seismogenic out‐of‐sequence thrusts in the Nankai accretionary prism: Comparison of laboratory‐derived physical properties and seismic reflection data

Tsuji, Takeshi; Kimura, Gaku; Okamoto, S.; Kono, Fumio; Mochinaga, Hisako; Saeki, Tatsuo; Tokuyama, Hidekazu

doi:10.1029/2006gl027025

Cited by 33 publications

(56 citation statements)

References 16 publications

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“…The deep mega-splay fault landward of the transition zone off Kumano has been imaged as a single reflector with strong reflection amplitude (Figure 2; Park et al 2002;Bangs et al 2009), indicating a large contrast in seismic velocity (Tsuji et al 2006;Kamei et al 2012), which in turn originates from large pore pressure contrast or difference in lithology. Overpressured fluid may be trapped by a low-permeability barrier along the deep mega-splay fault (e.g., Brown et al 1994).…”

Section: Discussionmentioning

confidence: 99%

Strike-slip motion of a mega-splay fault system in the Nankai oblique subduction zone

Tsuji

Ashi

Ikeda

2014

Earth, Planets and Space

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We evaluated the influence of the trench-parallel component of plate motion on the active fault system within the Nankai accretionary wedge from reflection seismic profiles, high-resolution seafloor bathymetry, and deep-towed sub-bottom profiles. Our study demonstrated that a large portion of the trench-parallel component of oblique plate subduction is released by strike-slip motion along a fault located just landward of and merging down-dip with a mega-splay fault. The shallow portion of the splay fault system, forming a flower structure, seems to accommodate dominant strike-slip motion, while most of the dip-slip motion could propagate to the trenchward décollement. Numerous fractures developed around the strike-slip fault release overpressured pore fluid trapped beneath the mega-splay fault. The well-developed fractures could be related to the change in stress orientation within the accretionary wedge. Therefore, the strike-slip fault located at the boundary between the inner and outer wedges is a key structure controlling the stress state (including pore pressure) within the accretionary prism. In addition, the strike-slip motion contributes to enhancing the continuous mega-splay fault system (outer ridge), which extends for approximately 200 km parallel to the Nankai Trough.

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Section: Discussionmentioning

confidence: 99%

Strike-slip motion of a mega-splay fault system in the Nankai oblique subduction zone

Tsuji

Ashi

Ikeda

2014

Earth, Planets and Space

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“…Porosity, resistivity, and P-wave velocity values may be influenced by cracks and fractures opened during unloading. Possible approaches to exclude the effect of cracks opened during exhumation include laboratory experiments under confining pressure and theoretical calculations for velocity and effective stress (Tsuji et al 2006;2008). In the current study, we quantified the physical property values of host rocks (intact zones), cohesive damage zones, and brecciated fracture zones.…”

Section: Data Acquisition and Methodology For Core-log Integrationmentioning

confidence: 99%

“…In addition to physical property measurements on samples from the outcrop of the Nobeoka Thrust (Tsuji et al 2006), Hamahashi et al (2013) documented physical properties near the main fault core from geophysical logs. Clear structural and physical property contrasts across the thrust were characterized, which are partially due to different maximum burial depths of the hanging wall and footwall ).…”

Section: Geologic Setting Of the Nobeoka Thrustmentioning

confidence: 99%

Multiple damage zone structure of an exhumed seismogenic megasplay fault in a subduction zone - a study from the Nobeoka Thrust Drilling Project

et al. 2015

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To investigate the mechanical properties and deformation patterns of megathrusts in subduction zones, we studied damage zone structures of the Nobeoka Thrust, an exhumed megasplay fault in the Kyushu Shimanto Belt, using drill cores and geophysical logging data obtained during the Nobeoka Thrust Drilling Project. The hanging wall, composed of a turbiditic sequence of phyllitic shales and sandstones, and the footwall, consisting of a mélange of a shale matrix with sandstone and basaltic blocks, exhibit damage zones that include multiple sets of 'brecciated zones' intensively broken in the mudstone-rich intervals, sandwiched by 'surrounding damage zones' in the sandstone-rich intervals with cohesive faults and mineral veins. The fracture zones are thinner (2.7 to 5.5 m) in the sandstone-rich intervals and thicker in the shale-dominant intervals (2.3 to 18.6 m), which indicates a preference of coseismic slip and velocity-weakening in the former, and aseismic deformation in the latter. However, the surrounding damage zones observed in the current study are associated with an increase in resistivity, P-wave velocity, and density and a decrease in porosity, inferring densification and strain-hardening in the sandstone-rich intervals and strain-weakening in the mudstone-rich intervals. These observations indicate that the sandstone-rich damage zones may weaken in the short term but may strengthen in the geologically long term, contributing to a later stage of fault activity. In contrast, the mudstone-rich damage zones may strengthen in the short term but develop weak structures through longer time periods. The observed shear zone thickness in the hanging wall is thinner (2.3 to 18.6 m) compared to the footwall damage zones (12 to 39.9 m), possibly because faults in the hanging wall were concentrated and partitioned between the preexisting turbiditic sequence of alternating shale/ sandstone-dominant intervals, whereas in the footwall, faults were more sporadically distributed throughout the sandstone block-in-matrix cataclasites. A splay fault may evolve and be characterized by physical property contrasts, the lithology dependence of deformation, and the variability of damage zone thickness due to a heterogeneous lithology distribution in the hanging wall and footwall. The deformation patterns observed in the Nobeoka Thrust provide insights to the strain-hardening/weakening behaviors of sediments along megathrusts over geological timescales.

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“…[16] Because the acoustic velocities of the core samples from Sites 1173, 1174, and 808 were not measured under confining stresses, we measured the velocities of outcrop samples from the Nobeoka thrust in Kyushu, southwestern Japan [Tsuji et al, 2006], and of seafloor outcrop samples obtained from the Nankai accretionary prism off the Kii Peninsula by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) submersible vessel Shinkai 6500. Although these samples were different from those of our study area, they do come from the Nankai accretionary prism.…”

Section: Laboratory-derived Velocitiesmentioning

confidence: 99%

Effective stress and pore pressure in the Nankai accretionary prism off the Muroto Peninsula, southwestern Japan

Tsuji¹,

Tokuyama²,

Pisani³

et al. 2008

J. Geophys. Res.

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[1] We developed a theoretical method for predicting effective stress and pore pressure based on rock physics model. We applied the method to reveal the pore pressure distribution within the Nankai accretionary prism off southwestern Japan and to investigate variations in pore pressure associated with evolution of the plate boundary décollement. From the crack aspect ratio spectrum estimated from laboratory and well-log data, we calculated a theoretical relationship between acoustic velocity and mean effective stress by using differential effective medium theory. By iteratively fitting the theoretically calculated velocity to the seismic velocities derived from 3D tomographic inversion, we estimated in situ mean effective stress within the accretionary prism. Pore pressure is then the difference between the effective stress and the confining stress. When we calculated pore pressure, we considered compressive state of stress in the accretionary prism. Our results confirm that pore fluid pressure is high within the subducting sedimentary sequence below the décollement; we determined a normalized pore pressure ratio (l*) of 0.4-0.7. Abnormal pore pressures develop in the underthrust sequence as a result of the increase in overburden load because of the thickened overlying prism and a low permeability barrier across the décollement. Overpressuring within the accreted sequence is initiated at the deformation front and proceeds landward. The increase in horizontal compaction within the accreted sequence may raise pore pressures within the accreted sequence, and the pore pressure (mean effective stress) contrast at the décollement becomes smaller landward of the deformation front.Citation: Tsuji, T., H. Tokuyama, P. Costa Pisani, and G. Moore (2008), Effective stress and pore pressure in the Nankai accretionary prism off the Muroto Peninsula, southwestern Japan,

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Modern and ancient seismogenic out‐of‐sequence thrusts in the Nankai accretionary prism: Comparison of laboratory‐derived physical properties and seismic reflection data

Cited by 33 publications

References 16 publications

Strike-slip motion of a mega-splay fault system in the Nankai oblique subduction zone

Strike-slip motion of a mega-splay fault system in the Nankai oblique subduction zone

Multiple damage zone structure of an exhumed seismogenic megasplay fault in a subduction zone - a study from the Nobeoka Thrust Drilling Project

Effective stress and pore pressure in the Nankai accretionary prism off the Muroto Peninsula, southwestern Japan

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