Dynamic changes in fluid redox state associated with episodic fault rupture along a megasplay fault in a subduction zone

Yamaguchi, Asuka; Cox, S. F. J.; Kimura, Gaku; Okamoto, S.

doi:10.1016/j.epsl.2010.12.029

Cited by 53 publications

(69 citation statements)

References 31 publications

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“…In fact, such vertical, extensional fault-fracture systems of different scales were reported from ancient accretionary prisms where fluid percolation along the fractures was exemplified by the formation of mineral veins precipitated from the solution. Sibson (2013) argued that different scales of extensional fault-fracture systems exist, which depend on the degree of release of seismic energy, and for example, one can refer to the large-scale Alsaska-Juneau Au deposit hosted by quartz veins (Goldfarb et al 1988;Miller et al 1994) and the small-scale quartz-carbonate veins in the Nobeoka thrust zone in the Shimanto accretionary complex in Kyushu, Japan (Yamaguchi et al 2011). The forearc horizontal extension immediately after the earthquakes is again succeeded by horizontal compression when the fractures along the megathrust are sealed by mineral veins and the strength is recovered.…”

Section: Discussionmentioning

confidence: 99%

Stress reversal recorded in calcite vein cuttings from the Nankai accretionary prism, southwest Japan

2014

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The Nankai Trough subduction zone in southwest Japan is a typical convergent margin where the Philippine Sea plate subducts in the northwest direction beneath the Eurasian plate, and devastating earthquakes have repeatedly occurred in this region in the past. In order to investigate the evolution of the stress state in the subduction zone, we analyzed deformation microstructures and the preferred orientation of calcite grains in two cuttings of calcite veins from Hole C0002F that was drilled through the inner wedge of the Nankai accretionary prism during the Integrated Ocean Discovery Program (IODP) Expedition 338 in 2012. For both samples collected at depths of 1,085.5 and 1,885.5 meters below the sea floor (mbsf), the c-axes of calcite grains are preferentially oriented perpendicular to the vein wall, which is indicative of competitive growth of calcite during the vein opening caused by a vein normal extension. Also, mechanical e-twins were developed in both samples, and these are inferred to have been developed under the same stress field as that responsible for the formation of calcite veins based on the paleostress analyses in grains with e-twins. For the calcite vein retrieved at the depth of 1,885.5 mbsf, kink bands were also developed by the compression in the direction perpendicular to the vein wall, which is indicative of stress reversal after the formation of mechanical e-twins. Although we could not reach a definite conclusion for the cause of the stress reversal, it could have occurred during either fold development or seismic cycles in the Nankai accretionary prism.

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Section: Discussionmentioning

confidence: 99%

Stress reversal recorded in calcite vein cuttings from the Nankai accretionary prism, southwest Japan

2014

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“…The fault core is bordered by phyllite overprinted by a brittle shear zone of several meter thickness in the hanging wall (Kondo et al 2005;Kimura et al 2013) and a footwall with a thickness of about 100 m (Kondo et al 2005;Yamaguchi et al 2011). Within the brittle damage zone of the hanging wall, pseudotachylyte-bearing faults and tension-crack-filling veins exist at high angles to the cleavage (Okamoto et al , 2007Kimura et al 2013).…”

Section: Geologic Setting Of the Nobeoka Thrustmentioning

confidence: 99%

“…The deformation of fault rocks in the footwall is brittle deformation accompanied by pressure solution as inferred from microstructural observations on quartz aggregates in sandstone blocks (Kondo et al 2005). Subsidiary fractures and a cataclastic composite planar fabric are categorized into types Y, R, P, and T (Logan et al 1981;Chester and Logan 1986) and are occasionally filled by mineral veins (Kondo et al 2005;Yamaguchi et al 2011).…”

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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“…Fault zones in exhumed accretionary complexes record fluid-rock interaction processes, many of which are interpreted in terms of a seismic cycle or coseismic fluid-rock interactions (Okamoto et al 2006;Meneghini and Moore 2007;Ujiie et al 2007a;Ishikawa et al 2008;Hamada et al 2011;Yamaguchi et al 2011aYamaguchi et al , 2012Kimura et al 2013).…”

Section: Fluid-rock Interactions In Fault Zonesmentioning

confidence: 99%

Earthquake faulting in subduction zones: insights from fault rocks in accretionary prisms

Ujiie

Kimura

2014

Prog Earth Planet Sci

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Subduction earthquakes on plate-boundary megathrusts accommodate most of the global seismic moment release, frequently resulting in devastating damage by ground shaking and tsunamis. As many earthquakes occur in deep-sea regions, the dynamics of earthquake faulting in subduction zones is poorly understood. However, the Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) and fault rock studies in accretionary prisms exhumed from source depths of subduction earthquakes have greatly improved our understanding of earthquake faulting in subduction zones. Here, we review key advances that have been made over the last decade in the studies of fault rocks and in laboratory experiments using fault zone materials, with a particular focus on the Nankai Trough subduction zone and its on-land analog, the Shimanto accretionary complex in Japan. New insights into earthquake faulting in subduction zones are summarized in terms of the following: (1) the occurrence of seismic slip along velocity-strengthening materials both at shallow and deep depths; (2) dynamic weakening of faults by melt lubrication and fluidization, and possible factors controlling coseismic deformation mechanisms; (3) fluid-rock interactions and mineralogical and geochemical changes during earthquakes; and (4) geological and experimental aspects of slow earthquakes.

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Dynamic changes in fluid redox state associated with episodic fault rupture along a megasplay fault in a subduction zone

Cited by 53 publications

References 31 publications

Stress reversal recorded in calcite vein cuttings from the Nankai accretionary prism, southwest Japan

Stress reversal recorded in calcite vein cuttings from the Nankai accretionary prism, southwest Japan

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

Earthquake faulting in subduction zones: insights from fault rocks in accretionary prisms

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