Language：Japanese   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2022.0_290

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We determine the features and distribution of fault rocks along the Median Tectonic Line (MTL), SW Japan, to establish the 3D architecture of the fault zone across the brittle-plastic transition. Cataclasites exposed close to the lithological boundary fault (the MTL) can be divided into those formed by sinistral faulting at temperatures of -300 degrees C and those formed by dextral faulting at -250 degrees C. Mylonites distributed to the north of the cataclasites were formed by sinistral faulting and can be divided into lower-temperature mylonite (L-T mylonite) close to the MTL and higher-temperature mylonite (H-T mylonite) distant from the MTL, where deformation temperatures were lower and higher than 400 degrees C, respectively. Structures formed by sinistral faulting are oblique to those formed by dextral faulting, indicating that the former structures are older than the latter. Structures formed by sinistral faulting underwent deformation around the brittle-plastic transition. Thus, the MTL fault zone records deformation through a crustal section. Microstructural observations suggest that the differential stress just below the brittle-plastic transition (L-T mylonite) was -200 MPa and that this value may not change substantially in the deep crust (H-T mylonite).

DOI： 10.1016/j.jsg.2021.104446

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Publishing type：Research paper (scientific journal)   Publisher：European Association of Geochemistry  

DOI： 10.7185/geochemlet.2131

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Publishing type：Research paper (scientific journal)  

Destructive landslides were triggered by the 6.7 Mw Eastern Iburi earthquake that struck southern Hokkaido, Japan, on 6 September 2018. Heavy rainfall on 4 September in addition to intermittent rainfall around the Iburi Tobu area saturated and weakened the slope-forming materials (mostly altered volcanoclastic soils), making them susceptible to failure because of the earthquake’s strong ground motion. Most of the shallow landslides exhibited long runouts along gentle hill slopes, with characteristic halloysite-bearing slip surface at the base of the volcanic soils. This study investigated the mineralogical and physico-chemical properties of the slip surface material with the aim of understanding weakening and post-failure behaviors during the landslides. Halloysite in the slip surface had irregular-to-hollow-spherical morphology with higher mesopore volumes than tubular halloysite, which is related to a high capacity for water retention after rainfall. To reproduce possible chemical changes in the slip surface during rainfall, the sample was immersed in varying amounts of rainwater; solution pH increased and ionic strength decreased with increasing water content. These findings, alongside electrophoretic analysis, suggest that rainwater infiltration could have increased the absolute zeta potential value of the slip surface material. It is suggested that rainfall before the earthquake enhanced the colloidal stability of halloysite particles within the slip surface, owing to an increase in electrostatic repulsion. This decreased the material’s cohesive strength, which might have led to destabilization of the slope during ground shaking generated by the earthquake, and subsequent high-mobility flow after failure. [Figure not available: see fulltext.].

DOI： 10.1186/s40645-021-00428-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Destructive landslides were triggered by the 6.7 M-w Eastern Iburi earthquake that struck southern Hokkaido, Japan, on 6 September 2018. In this study, we carried out 1-D inversion analysis of one of the shallow landslides near the epicenter using a Bing debris-flow model. At this site, the slope failure comprised cover soil with an initial down-slope length of similar to 80 m and a thickness of similar to 7 m on a slope with < 20 degrees dip. The landslide moved southeastward with a run-out distance of similar to 100 m. Inversion analysis of the post-failure deposit geometry was conducted with the Markov Chain Monte Carlo method (MCMC) to optimize the Bingham rheological parameters of the debris. The analysis reproduced several features of the deposit geometry with a yield stress of similar to 1500 Pa and dynamic viscosity of 800-3000 Pa s. The results suggest that the shallow landslide can be approximated by the flow of a viscoplastic fluid with high-mobility debris and a maximum frontal velocity of 6-9 m/s, with a flow duration of 2-4 min.

DOI： 10.1186/s40623-021-01443-y

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Language：English   Publishing type：Research paper (scientific journal)  

Submarine debris flows are mass movement processes on the seafloor, and are geohazards for seafloor infrastructure such as pipelines, communication cables, and submarine structures. Understanding the generation and run-out behavior of submarine debris flows is thus critical for assessing the risk of such geohazards. The rheological properties of seafloor sediments are governed by factors including sediment composition, grain size, water content, and physico-chemical conditions. In addition, extracellular polymeric substances (EPS) generated by microorganisms can affect rheological properties in natural systems. Here we show that a small quantity of EPS (~ 0.1 wt%) can potentially increase slope stability and decrease the mobility of submarine debris flows by increasing the internal cohesion of seafloor sediment. Our experiments demonstrated that the flow behavior of sediment suspensions mixed with an analogue material of EPS (xanthan gum) can be described by a Herschel-Bulkley model, with the rheological parameters being modified progressively, but not monotonously, with increasing EPS content. Numerical modeling of debris flows demonstrated that the run-out distance markedly decreases if even 0.1 wt% of EPS is added. The addition of EPS can also enhance the resistivity of sediment to fluidization triggered by cyclic loading, by means of formation of an EPS network that binds sediment particles. These findings suggest that the presence of EPS in natural environments reduces the likelihood of submarine geohazards.

DOI： 10.1038/s41598-021-81186-8

PubMed

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

After an earthquake, faults can recover strength through fault healing, but the mechanisms responsible are not well understood. Seismic slip may induce sintering, a bonding process between solid particles in contact under high temperatures without melting, which could produce a fault rock with elevated strength and chemical stability. Here we present results from electron microscope analyses that show a typical sintered structure in a black disk-shaped rock from the Chelungpu fault, Taiwan. This structure is experimentally reproducible in simulated fault material, prepared from the local host-rock, by heating at 800–900 °C. Through thermal and kinetic analyses of experimental materials, we show that sintering is an exothermic process which can generate energy to enhance post-slip thermochemical reactions in the fault. We propose that sintering substantially contributes to earthquake energetics and fault healing and that its occurrence can be a useful indicator of past seismic slip.

DOI： 10.1038/s43247-020-0004-z

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Other Link： http://www.nature.com/articles/s43247-020-0004-z

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.colsurfa.2020.125421

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DOI： 10.1038/s41598-019-48820-y

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1111/iar.12320

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1111/iar.12320

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier B.V.  

To better understand the factors that influence seafloor serpentinite mudflows, such as those recently documented on the Marianas seamounts, we have conducted rheological measurements on composite serpentine-brucite suspensions at 7 °C and a salt concentration of 0.6 M. The resulting flow curves were fitted by the Bingham fluid model, from which the Bingham yield stress and plastic viscosity of each suspension was determined. Both the yield stress and plastic viscosity increase as the water content of the suspension decreases. Increasing the brucite fraction in the solid mixture results in an increase in yield stress and a decrease in viscosity of the suspension for the same water/solid ratio. Physicochemical parameters such as pH, temperature and electrolyte concentration also moderately affect the rheology of the suspension, but the influence is not as significant as has been previously observed for suspensions containing smectite. The results suggest that mineral composition of the serpentinite mud, especially the abundance of brucite, has as much of an impact as water content on variable mudflow behaviors such as those observed at the Mariana seamounts.

DOI： 10.1016/j.margeo.2018.06.004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Dehydroxylation of clay minerals within fault gouges is significant for assessing transient thermogenesis due to high-velocity, frictional slip along fault zones. The clay minerals kaolinite and chlorite are common in fault zones hosted in sedimentary rocks at subduction margins. To better understand the dehydroxylation processes of these clay minerals, high-temperature X-ray diffraction analyses were carried out by using a 1:1 mixture of kaolinite and chlorite standard samples. We evaluated the kinetic parameters of each dehydroxylation reaction by thermogravimetric analysis using the Friedman method. For kaolinite, the thermogravimetric data are fitted with a one and a half order equation (F-3/2) with an activation energy of 171 kJ/mol and a frequency factor of 5.6 x 10(8) s(-1). The data for chlorite are analyzed by the geometrical contracting model equation (R-2) with an activation energy of 197 kJ/mol and a frequency factor of 4.5 x 10(9) s(-1). Thermal models of frictional heating employing this calibration show that the frictional heating can explain the reported clay mineralogy in a fossil imbricate thrust from a shallow part in an ancient accretionary prism (Shirako Fault, Japan). This result supports the previous assertion, and the observed temperature anomaly appears to demonstrate the frictional heating caused by coseismic slip on this fault.

DOI： 10.1029/2018GC007472

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Language：English   Publishing type：Research paper (scientific journal)  

Knowledge of rock thermal conductivity is necessary to understand the thermal structure in active seismogenic zones such as the Nankai Trough subduction zone, SW Japan. To estimate in situ thermal conductivity at the oceanic crust surface in the seismogenic zone, we measured the thermal conductivity of a basaltic basement core sample retrieved from subducting oceanic basement at the Nankai Trough Seismogenic Zone Experiment input site C0012 under high temperature (maximum 160 °C) and high pressure (maximum effective pressure 100 MPa), respectively. These conditions correspond to the in situ temperature and pressure at the oceanic crust surface in the updip limit of the Nankai seismogenic zone (~7 km below the seafloor). Thermal conductivity of the oceanic basalt is both temperature and pressure dependent. In contrast to other rock types such as sandstone and granite, for which thermal conductivity decreases with increasing temperature, the thermal conductivity of the oceanic basalt increased with increasing ambient temperature. The thermal conductivity of the basalt also increased with increasing effective pressure; however, the rate of increase was much lower than that for other rocks. These new temperature and pressure effect data for oceanic crust basalt fill a gap in the research. The estimated thermal conductivity of the basalt at in situ temperature and pressure conditions was less than ~2 W m -1 K -1 , although deformation and alteration associated with subduction could decrease pore spaces in the basalt, leading to enhanced thermal conductivity. This value is significantly lower than that typically assumed for thermal structure simulations in the Nankai subduction zone.

DOI： 10.1130/2018.2534(02)

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

Melt-origin pseudotachylyte is the most reliable seismogenic fault rock. It is commonly believed that pseudotachylyte generation is rare in the plate subduction zone where interstitial fluids are abundant and can trigger dynamic fault-weakening mechanisms such as thermal pressurization. Some recent studies, however, have discovered pseudotachylyte-bearing faults in exhumed ancient accretionary complexes, indicating that frictional melting also occurrs during earthquakes in subduction zones. To clarify the pseudotachylyte generation mechanism and the variation of slip behavior in the plate subduction zone, a pseudotachylyte found in the exhumed fossil accretionary complex (the Shimanto Belt, Nobeoka, Japan) was re-focused and microscopic and three-dimensional observations of the pseudotachylyte-bearing fault were performed based on optical, electron, and X-ray microscope images. Based on the patterns contained in the fragment, the pseudotachylyte is divided into four domains, although no clear domain boundaries or layering structures are not found. Three-dimensional observation also suggests that the pseudotachylyte were fragmented or isolated by cataclasite or carbonate breccia. The pseudotachylyte was rather injected into the surrounding carbonate breccia, which is composed of angular fragments of the host rock and a matrix of tiny crystalline carbonate. The pseudotachylyte volume was extracted from the X-ray microscope image and the heat abundance consumed by the pseudotachylyte generation was estimated at 2.18 MJ/m(2), which can be supplied during a slip of approximately 0.5 m. These observations and calculations, together with the results of the previous investigations, suggest hydrofracturing and rapid carbonate precipitation that preceded or accompanied the frictional melting. Dynamic hydrofracturing during a slip can be caused by rapid fluid pressurization, and can induce abrupt decrease in fluid pressure while drastically enhancing the shear strength of the shear zone. Consequently, frictional heating would be reactivated and generate the pseudotachylyte. These deformation processes can explain pseudotachylyte generation in hydrous faults with the impermeable wall rock.

DOI： 10.1111/iar.12241

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Language：English   Publishing type：Research paper (scientific journal)  

Deformation in a subduction zone and the related transition from smectite to illite within the aseismic-seismic transition zone (2-4 km below the seafloor) were analyzed by studying an onland accretionary complex that was previously buried to a depth of just 2-4 km. The early to middle Miocene Hota accretionary complex of central Japan is an excellent example of an accretionary complex that records shallow underthrusting at the updip end of the seismogenic zone. Two types of subduction-related deformation are preserved in the complex: phacoidal deformation (D1) characterized by rhombus-shaped fragments of mudstone with a random fabric and a thin rim of clay minerals with a preferred orientation, similar to the deformation features of the primary décollement zone at the toe of modern accretionary prisms (as revealed by ocean drilling); and block-in-matrix deformation (D2) characterized by an asymmetric S-C foliation with shear bands and an intense shape-preferred orientation of clay minerals, similar to the deformation features of tectonic mélange in ancient, mature décollement zones. D2 is marked by a large reduction in the amount of smectite and a corresponding increase in illite. During D2, the shear zone increased in strength due to the disappearance of weak smectite, which has a low friction coefficient, and due to an increase in the cohesion of sediments associated with a reduction in porosity and the development of a preferred orientation of clay minerals. Such strain hardening represents a fundamental mechanical/chemical change in the properties of sediments immediately before entering the seismogenic zone.

DOI： 10.1130/2018.2534

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Understanding the rheological properties of clay suspensions is critical to assessing the behavior of sediment gravity flows such as debris flow or turbidity current. We conducted rheological measurements of composite smectite-quartz suspensions at a temperature of 7 degrees C and a salt concentration of 0.6M. This is representative of smectite-bearing sediments under conditions on the seafloor. The flow curves obtained were fitted by the Bingham fluid model, from which we determined the Bingham yield stress and dynamic viscosity of each suspension. At a constant smectite-quartz mixing ratio, the yield stress and the dynamic viscosity tend to increase as the solid/water ratio of the suspension is increased. In the case of a constant solid/water ratio, these values increase with increasing smectite content in the smectite-quartz mixture. Additional experiments exploring differing physicochemical conditions (pH1.0-9.0; temperature 2-30 degrees C; and electrolyte (NaCl) concentration 0.2-0.6M) revealed that the influence of temperature is negligible, while pH moderately affects the rheology of the suspension. More significantly, the electrolyte concentration greatly affects the flow behavior. These variations can be explained by direct and/or indirect (double-layer) interactions between smectite-smectite particles as well as between smectite-quartz particles in the suspension. Although smectite is known as a frictionally weak material, our experimental results suggest that its occurrence can reduce the likelihood that slope failure initiates. Furthermore, smectite can effectively suppress the spreading distance once the slope has failed.

DOI： 10.1002/2017GL075334

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

Laboratory measurements for compressional and shear wave velocities (Vp and Vs, respectively) and porosity were conducted with core samples from the Nobeoka Thrust Drilling Project (NOBELL) under controlled effective pressure (5-65 MPa at 5 MPa intervals) and wet conditions. Samples were classified according to deformation texture as phyllite, foliated cataclasite, or non-foliated cataclasite. Measured values of Vp, Vs, and porosity are within a range of 5.17-5.57 km/s, 2.60-2.71 km/s, and 2.75-3.10 %, respectively, for phyllite; 4.89-5.23 km/s, 2.46-2.57 km/s, and 3.58-4.53 %, respectively, for foliated cataclasite; and 4.90-5.32 km/s, 2.51-2.63km/s, and 3.79-4.60 %, respectively, for non-foliated cataclasite, which are all consistent with the previous laboratory experiments conducted with outcrop samples under dry conditions. However, our results also indicate higher Vp and Vs and lower porosity than those measured by the previous studies that adopted the wire-line logging methods. The variations in Vp, Vs, and porosity are controlled by deformation structure and are greater for phyllite and foliated cataclasite than for non-foliated cataclasite.

DOI： 10.1111/iar.12198

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

The Nobeoka Thrust, an ancient megasplay fault in the Shimanto Belt, southwestern Japan, contains fault rocks from the seismogenic zone, providing an accessible analog of active megasplay faults in deep subduction settings. In this study, the paleostress along the Nobeoka Thrust was analyzed using multiple inversion techniques, including k-means clustering of fault datasets acquired from drillcores that intersected the thrust. The six resultant stress orientation clusters can be divided into two general groups: stress solutions with north-south-trending sigma(1) axes, and those with east-west-trending sigma(1) axes. These groups are characterized by the temporal changes for the orientations of the sigma(1) and sigma(3) principal stress axes that involve alternation between horizontal and vertical. The findings are probably due to a change in stress state before and after earthquakes that occurred on the fault; similar changes have been observed in active tectonic settings, such as the 2011 Tohoku-Oki earthquake (Japan).

DOI： 10.1111/iar.12193

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

The alteration and dehydration of predominantly basaltic subducting oceanic crustal material are thought to be important controls on the mechanical and hydrological properties of the seismogenic plate interface below accretionary prisms. This study focuses on pillow basalts exposed in an ancient accretionary complex within the Shimanto Belt of southwest Japan and provides new quantitative data that provide insight into clay mineral reactions and the associated dehydration of underthrust basalts. Whole-rock and clay-fraction X-ray diffraction analyses indicate that the progressive conversion of saponite to chlorite proceeds under an almost constant bulk-rock mineral assemblage. These clay mineral reactions may persist to deep crustal levels (similar to 320 degrees C), possibly contributing to the bulk dehydration of the basalt and supplying fluid to plate-boundary fault systems. This dehydration can also cause fluid pressurization at certain horizons within hydrous basalt sequences, eventually leading to fracturing and subsequent underplating of upper basement rock into the overriding accretionary prism. This dehydration-induced breakage of the basalt can explain variations in the thickness of accreted basalt fragments within accretionary prisms as well as the reported geochemical compositions of mineralized veins associated with exposed basalts in onland locations. This fracturing of intact basalt can also nucleate seismic rupturing that would subsequently propagate along seismogenic plate interfaces.

DOI： 10.1186/s40623-017-0635-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Thick accumulation of chert is a ubiquitous feature of old oceanic plates at convergent margins. In this study, we investigate chert fragments recovered by the Integrated Ocean Drilling Program expedition 343 at the Japan Trench where the 2011 Tohoku-Oki earthquake (M-w 9.0) occurred. This sample provides a unique opportunity to investigate in situ chert diagenesis at an active subduction margin and its influence on the kinematics of megathrust faulting. Our mineralogical analyses revealed that the chert is characterized by hydrous opal-CT and may therefore be highly deformable via pressure solution creep and readily accommodate shear strain between the converging plates at driving stresses of kilopascal order. As chert diagenesis advances, any further deformation requires stresses of &gt;100MPa, given the increasing transport distances for solutes as represented in cherts on land. The chert diagenesis is thus related to the mechanical transition from a weakly to strongly coupled plate interface at this margin.

DOI： 10.1002/2016GL071784

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Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.tecto.2016.12.017

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Subduction zones where old oceanic plate underthrusting occurs are characterized by thick pelagic sediments originating from planktonic ooze as well as cold thermal conditions. For a better understanding of dehydration from pelagic sediments and fluid behavior, which would play a key role in controlling the dynamics in the shallow portion of the subduction zone, as observed in the 2011 Tohoku earthquake and tsunami, we investigate cherts in a Jurassic accretionary complex in Japan. The microstructure and microchemistry of these cherts indicate dissolution of SiO2 from a pressure solution seam and precipitation of SiO2 to the "white chert layer," which would act as a fluid conduit. The amount of water necessary to precipitate SiO2 in the white chert is similar to 10(2) times larger than that produced by compaction and silica/clay diagenesis. Other fluid sources, such as hydrated oceanic crust or oceanic mantle, are necessary to account for this discrepancy in the fluid budget. A large amount of external fluid likely contributed to rising pore pressure along cold plate boundaries. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2016.07.030

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

To better understand physicochemical processes in smectite-rich fault zones, we examined exchangeable cation composition of samples from the slip zone of the 2011 Tohoku-oki earthquake (M(w)9.0) recovered by the Integrated Ocean Drilling Program Expedition 343. Our chemical analyses revealed that the exchangeable Ca2+ and Mg2+ are enriched in the slip zone, while Na+ is depleted. K+ shows a complicated depth profile probably due to K fixation. Based on fluid chemistry data, we estimated apparent selectivity coefficients of exchange reactions in the ternary Ca2+-Mg2+-Na+ system. The results suggest that the Na+ to Mg2+ exchange reaction on smectite might have progressed in the slip zone. One explanation for this feature is local progress of the reaction triggered by coseismic thermogenesis during the earthquake. Considering that the frictional property of smectite gouge is dependent on the exchangeable cation composition, chemical processes as observed in this study are intimately linked to physical aspect of smectite-bearing faults.

DOI： 10.1002/2016GL068283

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Bulk mineral assemblages of sediments and igneous basement rocks on the incoming Cocos Plate at the Costa Rica subduction zone are examined by X-ray diffraction analyses on core samples. These samples are from Integrated Ocean Drilling Program Expedition 334 reference Site U1381, similar to 5 km seaward of the trench. Drilling recovered approximately 100 m of sediment and 70 m of igneous oceanic basement. The sediment includes two lithologic units: hemipelagic clayey mud and siliceous to calcareous pelagic ooze. The hemipelagic unit is composed of clay minerals (similar to 50 wt.%), quartz (similar to 5 wt.%), plagioclase (similar to 5 wt.%), calcite (similar to 15 wt.%) and similar to 30 wt.% of amorphous materials, while the pelagic unit is mostly made up of biogenic amorphous silica (similar to 50 wt.%) and calcite (similar to 50 wt.%). The igneous basement rock consists of plagioclase (similar to 50-60 wt.%), clinopyroxene (similar to>25 wt.%), and saponite (similar to 15-40 wt.%). Saponite is more abundant in pillow basalt than in the massive section, reflecting the variable intensity of alteration. We estimate the total water influx of the sedimentary package is 6.9 m(3)/yr per m of trench length. Fluid expulsion models indicate that sediment compaction during shallow subduction causes the release of pore water while peak mineral dehydration occurs at temperatures of approximately similar to 100 degrees C, 40-30 km landward of the trench. This region is landward of the observed updip extent of seismicity. We posit that in this region the presence of subducting bathymetric relief capped by velocity weakening nannofossil chalk is more important in influencing the updip extent of seismicity than the thermal regime.

DOI： 10.1002/2015GC005837

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We have used sandbox experiments to explore the mechanics of the frontal prism structures documented by seismic reflection data and new borehole from IODP Expedition 343 (JFAST). This study investigated the effects of down-dip (normal to trench axis) variations in frictional resistance along a decollement on the structural development of the frontal wedges near subduction zones. Interpretation of seismic reflection images indicates that the wedge has been effected by trench-parallel horst-and-graben structures in the subducting plate. We performed sandbox experiments with down-dip patches of relatively high and low friction on the basal decollement to simulate the effect of variable coupling over subducting oceanic plate topography. Our experiments verify that high frictional resistance on the basal fault can produce the internal deformation and fault-and-fold structures observed in the frontal wedge by the JFAST expedition. Subduction of patches of varying friction caused a temporal change in the style of internal deformation within the wedge and gave rise to two distinctive structural domains, separated by a break in the surface slope of the wedge: (i) complexly deformed inner wedge with steep surface slope and (ii) shallow taper outer wedge, with a sequence of imbricate thrusts. Our experiments further demonstrate that the topographic slope-break in the wedge develops when the hinterland part of the wedge essentially stops deforming internally, leading to in-sequence thrusting with the formation of an outer wedge with low taper angle. For a series of alternate high and low frictional conditions on the basal fault the slope of the wedge varies temporally between a topographic slope-break and uniformly sloping wedge. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jog.2015.06.002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

Enormous earthquakes repeatedly occur in subduction zones, and the slips along megathrusts, in particular those propagating to the toe of the forearc wedge, generate ruinous tsunamis. Quantitative evaluation of slip parameters (i.e., slip velocity, rise time and slip distance) of past slip events at shallow, tsunamigenic part of the fault is critical to characterize such earthquakes. Here, we attempt to quantify these parameters of slips that may have occurred along the shallow megasplay fault and the plate boundary decollement in the Nankai Trough, off southwest Japan. We apply a kinetic modeling to vitrinite reflectance profiles on the two fault rock samples obtained from Integrated Ocean Drilling Program (IODP). This approach constitutes two calculation procedures: heat generation and numerical profile fitting of vitrinite reflectance data. For the purpose of obtaining optimal slip parameters, residue calculation is implemented to estimate fitting accuracy. As the result, the measured distribution of vitrinite reflectance is reasonably fitted with heat generation rate (Q) over dot and slip duration (t(r)) of 16,600 J/s/m(2) and 6,250 s, respectively, for the megasplay and 23,200 J/s/m(2) and 2,350 s, respectively, for the frontal decollement, implying slow and long-term slips. The estimated slip parameters are then compared with previous reports. The maximum temperature, Tmax, for the Nankai megasplay fault is consistent with the temperature constraint suggested by a previous work. Slow slip velocity, long-term rise time, and large displacement are recognized in these fault zones (both of the megasplay, the frontal decollement). These parameters are longer and slower than typical coseismic slip, but are rather consistent with rapid afterslip.

DOI： 10.1186/s40623-015-0208-0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：GEOLOGICAL SOC AMER, INC  

The very large slip on the shallow portion of the subduction interface during the 2011 Tohoku-oki earthquake (M-w 9.0) caused a huge tsunami along the northeast coast of Honshu, Japan. In order to elucidate the mechanics of such tsunamigenic slip, the Integrated Ocean Drilling Program Expedition 343 (Japan Trench Fast Drilling Project, JFAST), was carried out one year after the earthquake and succeeded in recovering rocks constituting the active plate boundary fault. Our mineralogical analyses using X-ray diffraction reveal that the shallow portion of the fault zone that caused the earthquake is significantly enriched in smectite compared to the surrounding sediments, which may be intimately linked to the tsunamigenic shallow faulting. For comparison, we also analyzed mineralogical features of incoming sediments just prior to subduction, recovered on the outer rise of the Japan Trench (Site 436, Deep Sea Drilling Project Leg 56), and found a characteristic smectite-rich horizon in the uppermost similar to 5 m of the pelagic clay layer. This horizon should be mechanically weak and will become the future plate boundary fault, as observed in the JFAST cores. The smectite-rich deposits are broadly distributed in the northwestern Pacific Ocean, and may therefore potentially enhance conditions for large shallow slip during earthquakes that occur over a broad area of the Japan Trench plate boundary, which would result in large tsunamis for this region.

DOI： 10.1130/G35948.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The 2011 Tohoku-Oki earthquake demonstrated that the shallowest reaches of plate boundary subduction megathrusts can host substantial coseismic slip that generates large and destructive tsunamis, contrary to the common assumption that the frictional properties of unconsolidated clay-rich sediments at depths less than similar to 5 km should inhibit rupture. We report on laboratory shearing experiments at low sliding velocities (&lt;1 mm/s) using borehole samples recovered during IODP Expedition 343 (JFAST), spanning the plate-boundary decollement within the region of large coseismic slip during the Tohoku earthquake. We show that at sub-seismic slip rates the fault is weak (sliding friction mu(s) = 0.2-0.26), in contrast to the much stronger wall rocks (mu(s) &gt; similar to 0.5). The fault is weak due to elevated smectite clay content and is frictionally similar to a pelagic clay layer of similar composition. The higher cohesion of intact wall rock samples coupled with their higher amorphous silica content suggests that the wall rock is stronger due to diagenetic cementation and low clay content. Our measurements also show that the strongly developed in-situ fabric in the fault zone does not contribute to its frictional weakness, but does lead to a near-cohesionless fault zone, which may facilitate rupture propagation by reducing shear strength and surface energy at the tip of the rupture front. We suggest that the shallow rupture and large coseismic slip during the 2011 Tohoku earthquake was facilitated by a weak and cohesionless fault combined with strong wall rocks that drive localized deformation within a narrow zone. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2014.12.014

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGEROPEN  

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 melange 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.

DOI： 10.1186/s40623-015-0186-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

The 2011 M(w)9.0 Tohoku-oki earthquake ruptured to the trench with maximum coseismic slip located on the shallow portion of the plate boundary fault. To investigate the conditions and physical processes that promoted slip to the trench, Integrated Ocean Drilling Program Expedition 343/343T sailed 1 year after the earthquake and drilled into the plate boundary approximate to 7 km landward of the trench, in the region of maximum slip. Core analyses show that the plate boundary decollement is localized onto an interval of smectite-rich, pelagic clay. Subsidiary structures are present in both the upper and lower plates, which define a fault zone approximate to 5-15m thick. Fault rocks recovered from within the clay-rich interval contain a pervasive scaly fabric defined by anastomosing, polished, and lineated surfaces with two predominant orientations. The scaly fabric is crosscut in several places by discrete contacts across which the scaly fabric is truncated and rotated, or different rocks are juxtaposed. These contacts are inferred to be faults. The plate boundary decollement therefore contains structures resulting from both distributed and localized deformation. We infer that the formation of both of these types of structures is controlled by the frictional properties of the clay: the distributed scaly fabric formed at low strain rates associated with velocity-strengthening frictional behavior, and the localized faults formed at high strain rates characterized by velocity-weakening behavior. The presence of multiple discrete faults resulting from seismic slip within the decollement suggests that rupture to the trench may be characteristic of this margin.

DOI： 10.1002/2014TC003695

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The 2011 Tohoku-Oki earthquake (Mw 9.0) produced a fault rupture that extended to the toe of the Japan Trench. The deformation and frictional properties beneath the forearc are keys that can help to elucidate this unusual event. In the present study, to investigate the frictional properties of the shallow part of the plate boundary, we applied the critically tapered Coulomb wedge theory to the Japan Trench and obtained the effective coefficient of basal friction (mu(b)') and Hubbert-Rubey pore fluid pressure ratio (lambda) of the wedge beneath the lower slope. We extracted the surface slope angle and decollement dip angle (which are the necessary topographic parameters for applying the critical taper theory) from seismic reflection and refraction survey data at 12 sites in the frontal wedges of the Japan Trench. We found that the angle between the decollement and back-stop interface generally decreases toward the north. The measured taper angle and inferred effective friction coefficient were remarkably high at three locations. The southernmost area, which had the highest coefficient of basal friction, coincides with the area where the seamount is colliding offshore of Fukushima. The second area with a high effective coefficient of basal friction coincides with the maximum slip location during the 2011 Tohoku-Oki earthquake. The area of the 2011 earthquake rupture was topographically unique from other forearc regions in the Japan Trench. The strain energy accumulation near the trench axis may have proceeded because of the relatively high friction, and later this caused a large slip and collapse of the wedge. The location off Sanriku, where there are neither seamount collisions nor rupture propagation, also has a high coefficient of basal friction. The characteristics of the taper angle, effective coefficient of basal friction, and pore fluid pressure ratio along the Japan Trench presented herein may contribute to the understanding of the relationship between the geometry of the prism and the potential for generating seismo-tsunamigenic slips.

DOI： 10.1186/s40623-014-0153-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGEROPEN  

Illite crystallinity (IC), the full width at half maximum of the illite (001) peak in clay-fraction X-ray diffraction (XRD), is a common geothermometer widely applied to various tectonic settings. Paleotemperature estimation using IC presents methodological ambiguity because IC is not only affected by background temperature but also by mechanical, hydrothermal, and surface weathering effects. To clarify the influences of these effects on IC in the fault zone, we analyzed the IC and the illite 001 peak intensity of continuous borehole core samples from the Nobeoka Thrust, a fossilized tectonic boundary thrust in the Shimanto Belt, the Cretaceous-Paleogene Shimanto accretionary complex in southwest Japan. We also carried out grinding experiments on borehole core samples and sericite standard samples as starting materials and investigated the effect of mechanical comminution on the IC and illite peak intensity of the experimental products. We observed the following: (1) the paleotemperatures of the hanging wall and footwall of the Nobeoka Thrust are estimated to be 288 degrees C to 299 degrees C and 198 degrees C to 249 degrees C, respectively, which are approximately 20 degrees C to 30 degrees C lower than their previously reported temperatures estimated by vitrinite reflectance; (2) the fault core of the Nobeoka Thrust does not exhibit IC decrease; (3) the correlation of IC and illite peak intensity in the hanging wall damage zone were well reproduced by the grinding experiment, suggesting that the effect of mechanical comminution increases toward the fault core and; (4) the abrupt increase in IC value accompanied by high illite peak intensity is explained by hydrothermal alterations including plagioclase breakdown and the formation of white micas. Our results indicate that IC has potential for quantifying the effects of mechanical comminution and hydrothermal alteration within a fault zone.

DOI： 10.1186/1880-5981-66-116

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

examined the frictional properties of sediments on the Cocos plate offshore the Osa Peninsula, Costa Rica, and explored variations in the intrinsic frictional properties of the sediment inputs to the Costa Rica subduction zone. Sediment samples were collected at Site U1381A during the Integrated Ocean Drilling Program Expedition 334, and include hemipelagic clay to silty clay material (Unit I) and pelagic silicic to calcareous ooze (Unit II). The frictional properties of the samples were tested at a normal stress of 5 MPa under water-saturated conditions and with slip velocities ranging from 0.0028 to 2.8 mm/s for up to 340 mm of displacement. The experimental results reveal that the steady-state friction coefficient values of clay to silty clay samples are as low as similar to 0.2, whereas those of silicic to calcareous ooze samples are as high as 0.6 to 0.8. The clay to silty clay samples show a positive dependence of friction on velocity for all tested slip velocities. In contrast, the silicic to calcareous ooze samples show a negative dependence of friction on velocity at velocities of 0.0028 to 0.28 mm/s and either neutral or positive dependence at velocities higher than 0.28 mm/s. Given the low frictional coefficient values observed for the clay to silty clay samples of Unit I, the decollement at the Costa Rica Seismogenesis Project transect offshore the Osa Peninsula likely initiates in Unit I and is initially very weak. In addition, the velocity-strengthening behavior of the clay to silty clay suggests that faults in the very shallow portion of the Costa Rica subduction zone are stable and thus behave as creeping segments. In contrast, the velocity-weakening behavior of the silicic to calcareous ooze favors unstable slip along faults. The shallow seismicity occurred at a depth as shallow as similar to 9 km along the Costa Rica margin offshore the Osa Peninsula (M-w 6.4, June 2002), indicating that materials characterized by velocity-weakening behavior constitute the fault zone at the depth of the seismicity. Fault slip nucleating along a fault in Unit II would be a likely candidate for the source of the shallow earthquake event.

DOI： 10.1186/1880-5981-66-72

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

The 2011 Tohoku earthquake (Mw 9.0) produced a very large slip on the shallow part of a megathrust fault that resulted in destructive tsunamis. Although multiple causes of such large slip at shallow depths are to be expected, the frictional property of sediments around the fault, particularly at coseismic slip velocities, may significantly contribute to large slip along such faults. We have thus investigated the frictional properties of incoming pelagic sediments that will subduct along the plate boundary fault at the Tohoku subduction zone, in order to understand the rupture processes that can cause large slip in the shallow parts of subduction zones. Our experimental results on clayey sediment at the base of the sedimentary section on the Pacific Plate yield a low friction coefficient of &lt;0.2 over a wide range of slip velocities (0.25 mm/s to 1.3 m/s), and extremely low fracture energy during slip weakening, as compared with previous experiments of disaggregated sediments under coseismic slip conditions. Integrated Ocean Drilling Program (IODP) Expedition 343 confirmed that the clay-rich sediment investigated here is identical to those in the plate boundary fault zone, which ruptured and generated the Tohoku earthquake. The present results suggest that smectite-rich pelagic sediment not only accommodates cumulative plate motion over interseismic periods but also energetically facilitates the propagation of earthquake rupture towards the shallow part of the Tohoku subduction zone.

DOI： 10.1186/1880-5981-66-65

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Because a megasplay fault branching from the deep subduction boundary megathrust in the Nankai Trough is thought to be the source of large tsunamis associated with past Tonankai earthquakes, investigation of the heat signal due to frictional slip recorded in the fault is important for estimating the earthquake slip parameters. We performed X-ray diffraction and infrared spectroscopic analyses of a megasplay fault-rock sample and re-examined previously reported trace-element and isotope compositions, but observed no specific change related to high temperature (&gt;= 250 degrees C). In addition, although a qualitative increase of the illite content in illite/smectite mixed-layer minerals within the slip-zone sample was previously reported, our kinetic evaluation of illitization, taking into consideration the coseismic temperature change due to frictional heating and heat conduction, revealed that the illitization reaction hardly progresses at temperatures under 250 degrees C. Alternatively, we suggest that the illite content in mixed-layer minerals might increase progressively via a comminution-dissolution-recrystallization process during multiple past slips. Accurate assessment of the slip behavior of the megasplay fault could be efficiently obtained by drilling to penetrate the fault zone at a deeper depth of approximately 1.5 km, where records of high temperatures would be detectable. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2014.04.020

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

We determined mineral assemblages of samples from the Taiwan Chelungpu fault and from milling and heating experiments by using X-ray diffraction and scanning and transmission electron microscopy. The fault system contains three dominant fault zones, the shallowest of which slipped during the 1999 Chi-Chi earthquake. The quartz and clay mineral contents of the primary slip zone were low, and it contained partly amorphous ultrafine particles (several tens of nanometers). Up to 30 weight percent of materials in that zone could not be fit to standard diffraction patterns, whereas nearly 100 weight percent of those in surrounding samples could be. The unfitted component could be attributed to the observed ultrafine particles produced by comminution during the earthquake, because weak diffraction intensities are caused from mineral lattice distortion, granulation, and amorphous coatings. Such particles are a potential proxy for identifying the slip zone of the most recent earthquake along a fault.

DOI： 10.1002/2014GL059805

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

We carried out geochemical and mineralogical analyses on fault-zone rocks from the Anko section of the Median Tectonic Line in Nagano Prefecture, Japan, to investigate coseismic physicochemical processes in the fault zone. The latest fault zone in the Anko section contains cataclasite, fault breccia, and fault gouge of granitic composition, and brecciated basic schist. Protoliths of the granitic composition are from the Ryoke metamorphic belt and those of the basic schist from the Sambagawa metamorphic belt. X-ray diffraction analyses show a selective decrease of clay minerals coupled with an increase of amorphous phase in an intensely deformed layer of black gouge (5- to 10-cm thick). SEM observation reveals that the black gouge is characterized by a drastic reduction of grain size and abundant ultrafine particles of submicrometer to several tens of nanometers with well-rounded spheroidal shapes. These observations for the black gouge are indicative of strong mineral lattice distortion and granulation associated with earthquake slip. Geochemically, the black gouge is characterized by distinctly higher Li content and Sr-87/Sr-86 isotope ratio than surrounding cataclasites, breccias, and gouges, which have similar major element compositions. Model analysis reveals that the trace element composition of the black gouge is consistent with high-temperature (up to 250A degrees C) coseismic fluid-rock interactions. Thermal and kinetic constraints indicate that there have been repeated slips on the fault at moderate depths (e.g., 600 m), although the tectonic process by which the fault zone has been uplifted and exposed in this area is not well understood.

DOI： 10.1186/1880-5981-66-36

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We present a quantitative examination of the liberation and subsequent deposition of silica at the subduction zone plate interface in the Mugi melange, an exhumed accretionary complex in the Shimanto Belt of southwest Japan. Frequency and thickness measurements indicate that mineralized veins hosted in deformed shales make up approximately 0.4% of the volume of this exposure. In addition, whole-rock geochemical evidence suggests that the net volume of SiO2 liberated from the melange at temperatures of < 200 degrees C was as much as 35%, with up to 40% of the SiO2 loss related to the smectite-illite (S-I) conversion reaction, and the rest attributable to the pressure solution of detrital quartz and feldspar. Kinetic modeling of the S-I reaction indicates active liberation of SiO2 at approximately 70 degrees C to 200 degrees C, with peak SiO2 loss at around 100 degrees C, although these estimates should be slightly shifted toward lower temperature conditions based on X-ray diffraction (XRD) analyses of mixed-layer S-I in the Mugi melange. The onset of pressure solution was not fully constrained, but has been documented to occur at around 150 degrees C in the study area. The deposition in deformed shales of quartz liberated by pressure solution and the S-I reaction is probably linked to seismogenic behavior along the plate interface by (1) progressively enhanced velocity-weakening properties, which are favorable for unstable seismogenic faulting, including very-low-frequency earthquakes and (2) increasing intrinsic frictional strength, which leads to a step-down of the plate boundary decollement into oceanic basalt.

DOI： 10.1186/1880-5981-66-13

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN ASSOC MINERALOGICAL SCIENCES  

We have examined the mineralogy and deformation of black shear zones containing abundant carbonaceous materials (CM) and clay minerals in bedded ribbon cherts in a Jurassic accretionary complex, central Japan. Microtextural observations indicate that pressure solution and cataclastic deformation were the primary deformation mechanisms in the cherts. Whole-rock mineral compositions were quantitatively investigated using X-ray diffraction, Raman spectroscopy, and a CHN elemental analyzer. The results show that the samples contain variable amounts of CM and clay minerals, up to 17 wt% and 60 wt%, respectively. Moreover, the clay and CM contents in the samples, including the host rock cherts, show a positive correlation represented by a single compositional trend, and this may be explained by the progressive concentration of clays and CM due to pressure solution and the removal of soluble quartz or mass transfer processes associated with deformation. Intact cherts dominated by quartz seem to provide plausible source rocks for the nucleation of seismic slip including slow slip events, while the abundant CM and clays as observed in the black shear zones may have effectively weakened and stabilized the sliding behavior. These results are important for understanding deformation processes in the Japan Trench.

DOI： 10.2465/jmps.140403

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC ADVANCEMENT SCIENCE  

The mechanics of great subduction earthquakes are influenced by the frictional properties, structure, and composition of the plate-boundary fault. We present observations of the structure and composition of the shallow source fault of the 2011 Tohoku-Oki earthquake and tsunami from boreholes drilled by the Integrated Ocean Drilling Program Expedition 343 and 343T. Logging-while-drilling and core-sample observations show a single major plate-boundary fault accommodated the large slip of the Tohoku-Oki earthquake rupture, as well as nearly all the cumulative interplate motion at the drill site. The localization of deformation onto a limited thickness (less than 5 meters) of pelagic clay is the defining characteristic of the shallow earthquake fault, suggesting that the pelagic clay may be a regionally important control on tsunamigenic earthquakes.

DOI： 10.1126/science.1243719

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC ADVANCEMENT SCIENCE  

Large coseismic slip was thought to be unlikely to occur on the shallow portions of plate-boundary thrusts, but the 11 March 2011 Tohoku-Oki earthquake [moment magnitude (M-w) = 9.0] produced huge displacements of similar to 50 meters near the Japan Trench with a resultant devastating tsunami. To investigate the mechanisms of the very large fault movements, we conducted high-velocity (1.3 meters per second) friction experiments on samples retrieved from the plate-boundary thrust associated with the earthquake. The results show a small stress drop with very low peak and steady-state shear stress. The very low shear stress can be attributed to the abundance of weak clay (smectite) and thermal pressurization effects, which can facilitate fault slip. This behavior provides an explanation for the huge shallow slip that occurred during the earthquake.

DOI： 10.1126/science.1243485

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1002/2013gc004818

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Fossil imbricate thrusts, branching from a decollement in an ancient accretionary prism (the Miura-Boso accretionary prism), are exposed in the southern parts of the Miura and Boso peninsulas in central Japan. An analysis of the clay mineralogy of fault rocks along one of the imbricate thrust faults, the Shirako Fault, revealed local illitization of mixed-layer illite-smectite (I-S) and the partial breakdown of kaolinite. The shape of the I(001)-S(001) reflection in the X-ray diffraction pattern suggests that the illite fraction in I-S crystallites within the fault gouge is similar to 9% more than in the surrounding rocks. These results imply that there has been a local temperature anomaly within the slip zone, attributable to frictional heating induced by high-velocity slip. A thermal model, coupled with a kinetic simulation of illitization in I-S, suggests that the reaction was probably facilitated by multiple high-velocity slips at a peak temperature of similar to 450 degrees C, suggesting repeated seismic rupture propagations to the prism toe, as also inferred from the modern accretionary prism (in the Nankai Trough). (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2013.04.024

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The structure and occurrence of deformation within the hanging wall of the Nobeoka Thrust in Kyushu, Japan, was investigated to understand the dynamic aspects of splay faulting in relation to seismic events. From field observations, hanging wall is suggested to have undergone four phases of deformation. The first phase involved horizontal shortening, as documented by folding and thrusting, followed by a phase of vertical loading shown by the development of horizontal slaty cleavages, pressure solution, and cleavage-parallel mineral vein precipitation. A third phase involved shearing, and deformation along cleavage restricted to near the Nobeoka Thrust, while the fourth phase produced widespread, brittle fracturing associated with the development of pseudotachylyte-bearing faults and tension crack filling veins high angle to cleavage. These four phases can be explained as follows.During the inter-seismic period, an extensionally stable taper was maintained in the inner wedge of the accretionary prism by dominant vertical loading (sigma 1), in combination with a lesser amount of horizontal compression (sigma 2) related to the locking of the mega-thrust. Elastic strain energy in the hanging wall of the inner wedge was co-seismically released by slip on the mega-thrust and horizontal shortening in the outer wedge associated with dynamic ductile weakening of the fault plane. This sudden release of elastic strain caused brittle fracturing with sigma 1 at a high angle to the shear surface of the Nobeoka Thrust, most of the displacement resulting from deformation of the footwall. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jsg.2013.03.015

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Recent analyses of natural faults and laboratory rock friction experiments have revealed that physical transformations and chemical reactions of minerals and fluids occur in faults during earthquakes. However, exactly how these physicochemical processes affect fault weakening and earthquake energetics is not well understood. We present quantitative experimental evidence of mechanochemical changes in a clay mineral (illite) during frictional slip and evaluate the effect of those changes on slip behavior. Friction distorts the crystal structure of illite and dramatically decreases the activation energy (E-a) of the dehydroxylation reaction. Numerical modeling shows that the lower E-a allows the dehydroxylation to occur at relatively low temperatures (200-300 degrees C), which in turn drastically reduces fault strength by pressurization of released water from the mineral. Thus, dynamic thermo-chemo-mechanical processes can strongly affect earthquake instability, especially along clay-rich faults such as those in the shallow part of subduction zone plate boundaries.

DOI： 10.1002/grl.50609

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

Very-low-frequency earthquakes (VLFE) occur within accretionary prisms and near subduction plate boundaries at slip rates of 0.05-2 mm/s. However, the geological and frictional aspects of VLFE remain poorly understood. The thrusts in the Shimanto accretionary complex exhumed from source depths of VLFE are composed of quartz-rich fault rocks with or without clay foliations. We examined the frictional velocity dependence of thrust materials. At slip rates of 0.0028-0.28 mm/s, the powder sample from non-foliated fault rock shows velocity-weakening behavior, while that from foliated fault rock exhibits velocity-strengthening behavior. Both samples show velocity-strengthening behavior at slip rates of 0.28-2.8 mm/s. Microstructural analysis reveals that the velocity-weakening sample shows a shear localization, while the velocity-strengthening sample is marked by clay foliations oblique and parallel to shear zone boundaries. Our results imply that frictional instability generates along quartz-rich fault rock but slip becomes stable at higher slip rates, regardless of mineral composition. This is favorable for the occurrence of VLFE in subduction zones. Key Points Quartz-rich fault rock exhibits velocity-weakening behavior Quartz-rich fault rock is not unusual in accretionary prisms Frictional properties of thrust materials may explain the occurrence of VLFE ©2013. American Geophysical Union. All Rights Reserved.

DOI： 10.1002/grl.50175

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The 2011 moment magnitude 9.0 Tohoku-Oki earthquake produced a maximum coseismic slip of more than 50 meters near the Japan trench, which could result in a completely reduced stress state in the region. We tested this hypothesis by determining the in situ stress state of the frontal prism from boreholes drilled by the Integrated Ocean Drilling Program approximately 1 year after the earthquake and by inferring the pre-earthquake stress state. On the basis of the horizontal stress orientations and magnitudes estimated from borehole breakouts and the increase in coseismic displacement during propagation of the rupture to the trench axis, in situ horizontal stress decreased during the earthquake. The stress change suggests an active slip of the frontal plate interface, which is consistent with coseismic fault weakening and a nearly total stress drop.

DOI： 10.1126/science.1229379

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The Costa Rica Seismogenesis Project (CRISP) is an experiment to understand the processes that control nucleation and seismic rupture of large earthquakes at erosional subduction zones. Integrated Ocean Drililng Program (IODP) Expedition 334 by R/V JOIDES Resolution is the first step toward deep drilling through the aseismic and seismic plate boundary at the Costa Rica subduction zone offshore the Osa Peninsula where the Cocos Ridge is subducting beneath the Caribbean plate. Drilling operations included logging while drilling (LWD) at two slope sites (Sites U1378 and U1379) and coring at three slope sites (Sites U1378-1380) and at one site on the Cocos plate (Site U1381). For the first time the lithology, stratigraphy, and age of the slope and incoming sediments as well as the petrology of the subducting Cocos Ridge have been characterized at this margin. The slope sites recorded a high sediment accumulation rate of 160-1035m m.y.-1 possibly caused by on-land uplift triggered by the subduction of the Cocos Ridge. The geochemical data as well as the in situ temperature data obtained at the slope sites suggest that fluids are transported from greater depths. The geochemical profiles at Site U1381 reflect diffusional communication of a fluid with seawater-like chemistry and the igneous basement of the Cocos plate (Solomon et al., 2011
Vannucchi et al., 2012a). The present-day in situ stress orientation determined by borehole breakouts at Site U1378 in the middle slope and Site U1379 in the upper slope shows a marked change in stress state within ~12 km along the CRISP transect
that may correspond to a change from compression (middle slope) to extension (upper slope).

DOI： 10.2204/iodp.sd.15.03.2013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

An assemblage of quantitative data sets is examined to evaluate tectonic melange as a plate boundary fault rocks in subduction zone. The research object is the latest Cretaceous Mugi melange in the Shimanto Belt, southwest Japan. Systematic age younging from pelagic to terrigenous through hemipelagic sediments is well-documented even though original stratigraphy is disrupted. Systematic shear fabric consistent with ancient plate convergence is reconstructed. The melange was formed at temperatures of similar to 130-200 degrees C by cataclastic comminution of sandstone layers accompanied by tensile cracking, and plastic deformation and the dehydration of clayey shale matrix, with subsequent peeling off and underplating of the oceanic basement.The temperature setting for the Mugi melange indicates around the up-dip limit of the seismogenic zone, therefore includes various fault rocks suggestive of earthquake fault; pseudotachylyte, fluidized ultracataclasite with heating evidence, amorphous silica and so on. These suggest that fluid induced lubrication was dominated. Localized cataclastic shear, which is a candidate of small earthquake or very low frequency earthquake, is also recognized especially in sandstone blocks dominated portion in melange. These observations are consistent with the melange being a fault rock along the plate boundary that records various types of earthquakes in a subduction zone. The quantitative examination of the Mugi melange suggests several criteria to define the tectonic melange of the plate boundary fault in subduction zone from other melanges in orogenic belt. (c) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2011.08.025

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The gigantic 2011, March 11 Mw 9 Tohoku earthquake is examined from the viewpoint of the pre-seismic forearc structure, the seismic reflection properties of a megathrust around the usual up-dip limit of the seismogenic zone, the thermal state of a shallow subduction zone, and the dehydration of underthrust sediments.At the Japan Trench the Pacific Plate is subducting westward beneath northeast Japan at a dip angle of 4.6 degrees. The middle and lower slopes of the landward side dip eastward at angles of similar to 2.5 degrees and similar to 8.0 degrees, respectively. The forearc prism beneath the middle and lower slopes is inferred to be in extensionally and compressively critical states, respectively, based on the presence of clear internal deformation features and on the occurrence of aftershock earthquakes. The rapid uplift of the forearc that caused the 2011 Tohoku tsunami may have been associated with this internal deformation of the prism. The critical state of the prism indicates that the effective basal friction (mu(b)') of the plate boundary megathrust is <0.03 for the middle prism and >0.08 for the lower prism.The megathrust, especially under the middle slope, is characterized by a prominent reflector with negative polarity. One of multiple possible explanations is that the megathrust hosts highly pressurized fluids. Underthrust sediments in this part of the Japan Trench are dominated by pelagic and siliceous vitric diatomaceous silt with clay. The dehydration kinetics of opal-A to quartz, the clay transformation of smectite-illite, and the thermal structure of the Japan Trench suggest that maximum dehydration of the sediments would take place at 50-60 km horizontally from the deformation front, where the temperature along the megathrust is 100-120 degrees C. The zone of maximum dehydration coincides with the prominent seismic reflector that has negative polarity. We hypothesize a possible free slip along this portion of the megathrust during the 2011 Tohoku earthquake, caused by anomalously high fluid pressure resulting from fluid accumulation over centuries. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2012.04.002

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The diagenesis and deformation processes of ribbon cherts embedded in a Jurassic accretionary complex, central Japan, were investigated in detail to gain a better understanding of the mechanical behavior of the plate boundary at depth in cold subduction zones. The analyzed cherts record two stages of deformation: (1) map-to outcrop-scale ductile folding, and (2) subsequent brittle faulting. The ductile deformation was facilitated by silica dehydration precipitation, and is represented by multiple phases of vein networks. The folds are cut by brittle faults, indicating lithification and the concurrent mechanical transition from ductile to brittle behavior. Slip zones along the faults are typically filled with brecciated chert in a chlorite matrix. Geothermometry analysis of the matrix chlorite suggests that faulting occurred following the completion of opal-CT to quartz transition reaction. This is also confirmed by the kinetic simulation of silica conversion reactions. The results suggest that ductile deformation of thick pelagic deposits with abundant fluids results in an aseismic plate boundary, whereas chemical diagenesis of the deposits, producing crystalline cherts, results in interplate coupling in cold subduction zones such as the Japan Trench. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2011.11.041

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Seismogenic plate-boundary faults at accretionary margins (e.g., the Nankai margin, southwest Japan) may occur where the uppermost part of subducting oceanic crust, composed of basaltic rocks, is in contact with the overriding plate of a lithified accretionary prism. The plate-boundary faults in ancient accretionary complexes typically record high-velocity slip under fluid-rich conditions. Although previous studies have emphasized the mechanical significance of fluids in terms of dynamic slip-weakening, the source of fluid in seismogenic subduction zones remains poorly constrained. In this work, we focus on the hydrous smectite in the uppermost oceanic crust, an alteration product of intact basalt before arrival at the trench axis. A comparison between (1) new mineralogical data on basalt drillcore recovered by Integrated Ocean Drilling Program (IODP) Expedition 322 at site C0012, a reference site for subduction input to the Nankai Trough, and (2) mineralogical data on basalt within ancient oceanic crust embedded in a fossil accretionary complex of the Shimanto Belt, southwest Japan, suggests that progressive smectite-chlorite conversion would liberate bound fluids at a rate of 0.34 to 0.65 x 10(-14) s(-1) along the plate interface. This rate of fluid production appears to be more than an order of magnitude greater than that from other possible sources, including from overlying sediments via smectite-illite conversion and the expulsion of pore fluids, and may facilitate seismic slip along plate-boundary faults. Citation: Kameda, J., A. Yamaguchi, S. Saito, H. Sakuma, K. Kawamura, and G. Kimura (2011), A new source of water in seismogenic subduction zones, Geophys. Res. Lett., 38, L22306, doi:10.1029/2011GL048883.

DOI： 10.1029/2011GL048883

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：GEOLOGICAL SOC AMER, INC  

The question of whether coseismic ruptures along megasplay faults in accretionary prisms (i.e., large landward-dipping thrust faults branching from the plate boundary) reach the seafloor is critical for assessing the risk of tsunami disaster. However, samples from active megasplay faults have not previously been available. Here we present geochemical and mineralogical data of megasplay fault samples obtained from the shallow (&lt;300 m below seafloor) portion of the megasplay fault that coincides with the rupture area of the A. D. 1944 Tonankai earthquake in the Nankai Trough. The megasplay fault zone is characterized by localized shear zones of brecciated host rocks. A prominent slip zone, here termed "dark gouge," was discovered within one of the shear zones. Compared to the surrounding breccias, the dark gouge is chemically enriched in Al and K, and depleted in Ca and Sr. It is also characterized by higher illite content in illite-smectite mixed-layer clays. These chemical and mineralogical features may reflect a transformation in clay mineralogy caused by frictional heating, and suggest that the seismic slip can propagate to very shallow levels along megasplay fault systems.

DOI： 10.1130/G32038.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

An ancient subduction thrust, developed at the top of oceanic basaltic crust, is exposed in the Shimanto accretionary complex of eastern Shikoku, southwest Japan. The fault zone structure indicates that slip was localized along a few centimeters-thick layer in which fluidization of comminuted material is recorded. To identify possible clay mineral reactions during frictional heating along subduction thrusts, we examined the clay mineralogy of the basalt-derived fault zone rocks, including ultracataclasite, altered basalt, foliated cataclasite, and massive basalt. All samples include chlorite, mixed-layer chlorite/smectite (C/S), and corrensite. Among the samples, the highest chlorite content in the C/S is found in the ultracataclasite. The significant chloritization in the ultracataclasite is unlikely to reflect hydrothermal alteration and regional very-low-grade metamorphism during subduction down to seismogenic depths; instead, it is interpreted to have resulted from frictional heating associated with localized slip. Based on chlorite geothermometry and the presence of small quantities of corrensite, we estimate the temperatures during this frictional heating to have been in the range of 185-260 degrees C, which is 35-130 degrees C higher than the ambient temperature. This difference of 35-130 degrees C is consistent with a temperature rise of 50-150 degrees C indicated by the stretching of fluid inclusions in calcite. Therefore, the crystallographic and chemical properties of C/S are potentially useful in detecting small temperature rises associated with frictional heating, and the method could be widely applicable to C/S-bearing faults. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2011.02.051

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Reactions involving clay minerals during low-grade metamorphism at the depth of an ancient accretionary complex in the Shimanto Belt, Kyushu, Japan, were studied by integrated transmission electron microscopy-energy dispersive X-ray spectroscopy and X-ray diffraction analyses of the bulk rock and clay fraction. The analyzed metasediment (the Kitagawa unit) contain an incipient sub-horizontal slaty cleavage. Illite crystallinity data and mica b dimensions indicate that the conditions of metamorphic deformation were anchizone-epizone grade and intermediate pressure. Cleavage formation was linked to two reactions involving clay minerals: (1) the recrystallization of 1M-dominant matrix mica, inherited from the original sedimentary fabric, into thick, defect-free 2M(1) packets along cleavage planes; and (2) the formation of chlorite from 7 angstrom berthierine. Balanced equations among the clay phases, based on compositional data and their relative abundance, suggest that the decomposition of matrix mica resulted in the formation of paragenetic mica and chlorite along the cleavage planes, without significant elemental outflux. Although a modal increase in phyllosilicates is not indicated by the data, the growth of chlorite and mica along cleavage planes may have a large influence on the rheological properties of a decollement and may be related to the occurrence of the seismic-aseismic transition at similar to 350 degrees C. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2011.02.010

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Language：English   Publisher：一般社団法人 日本粘土学会  

Mineralogy of Asian dust collected in Fukuoka, Southwest Japan, was investigated using X-ray diffraction (XRD) and scanning/transmission electron microscopy (SEM/TEM) in detail. The dust consisted of only silicates; quartz, albite, orthoclase, amphibole and phyllosilicates (muscovite/illite, biotite, chlorite, kaolin group minerals and smectite). This mineral composition for silicates is very close to that of a certified reference specimen for Asian dust (CJ-1) which was collected from the loess plateau in China. However, carbonate minerals abundant in CJ-1 are missing in Fukuoka dust. Probably the carbonate and other water-soluble minerals were dissolved by rain or during sample collection using water. Observation and X-ray chemical analysis in SEM revealed their morphologies and chemical compositions. Amphibole, biotite and chlorite are major Fe-bearing minerals in the dust. Among them, fine chlorite particles may be a good Fe-supplier for microorganism living in the shallow area of the ocean.

DOI： 10.11362/jcssjclayscience.15.1_43

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Language：English   Publishing type：Research paper (scientific journal)  

We examine the frictional properties and microstructures of clay-rich fault gouges subjected to thermal pressurization and fluidization, generated in high-velocity friction experiments under dry and wet conditions. In the dry tests, slip weakening occurs by thermal pressurization, which is marked by a fault-gouge expansion associated with a water-phase transition from liquid to vapour. The water is derived from dehydration of clay minerals by frictional heating. The resulting microstructure in the gouge layer is a random distribution of spherical clay-clast aggregates in the matrix, and mixing of different gouge constituents without shear surfaces. In the wet tests, slip weakening is caused by pore-fluid pressurization resulting from shear-enhanced compaction of the water-saturated gouge and frictional heating. Compared to the dry tests, the wet tests show smaller dynamic stress drops and slip weakening distance. The steady-state shear stress in the wet tests is almost independent of normal stress, suggesting a fluid-like behaviour of the fault gouge during high-velocity shearing. The microstructures after the wet tests show that the foliated zone is accompanied by grain-size segregation in the gouge layer. The grain-size segregation is attributed to the Brazil-nut effect resulting from the difference in dispersive pressure in the granular- fluid shear flow at high shear rates, indicating a fluidization of fault gouge. Our results obtained at seismic slip rates imply that the propagation of an earthquake rupture can be enhanced by fluid pressurization and frictional heat, potentially leaving characteristic microstructures resulting from water vaporization by frictional heating or flow sorting at high slip rates. © The Geological Society of London 2011.

DOI： 10.1144/SP359.15

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

An analysis of the mineralogy of the Miura-Boso accretionary prism, which consists of off-scraped upper Miocene strata exposed on the southern parts of the Miura and Boso peninsulas in Central Japan, revealed homogeneous mineral composition throughout all levels of silt layers hosting deformation structures associated with sediment accretion. XRD analyses showed that the sediment consists of randomly ordered mixed layer illite-smectite (I-S) with low illite content (&gt;40 wt.%), quartz (30 wt.%), illite (10-20 wt.%), plagioclase (10 wt.%), kaolinite (+ chlorite) (5 wt.%), and calcite (0-10 wt.%). The observed mineralogical assemblage indicates that location of the decollement formation was not constrained by mechanical heterogeneities associated with mineralogical variations, but was controlled by spatial variations in effective pressure. Within the over-consolidated sediment located above the incipient decollement zone, the occurrence of abundant smectite with a shape-preferred orientation gave rise to smectite swelling, producing pressures in the order of similar to 3.0 MPa. The combined effect of high swelling pressure and high pore pressure resulted in an overpressured zone at the base of the over-consolidated zone, facilitating the development of a decollement zone within the prism. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2010.08.008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

The microstructure and its crystallographic aspect of the shell of a limpet, Lottia kogamogai, have been investigated, as the first step to clarify the mechanism of shell formation in limpet. The shell consists of five distinct layers stacked along the shell thickness direction. Transmission electron microscopy (TEM) with the focused ion beam (FIB) sample preparation technique was primarily adopted, as well as scanning electron microscopy (SEM) with electron back-scattered diffraction (EBSD). The five layers were termed as M + 3, M + 2, M + 1, M, M - 1 from the outside to the inside in previous works, where M means myostracum. The outmost M + 3 layer consists of calcite with a "mosaic" structure; granular submicron sub-grains with small-angle grain boundaries often accompanying dislocation arrays. M + 2 layer consists of flat prismatic aragonite crystals with a leaf-like cross section, stacked obliquely to the shell surface. It looks that the prismatic crystals are surrounded by organic sheets, forming a compartment structure. M + 1 and M 1 layers adopt a crossed lamellar structure consisting of aragonite flat prisms with rectangular cross section. M layer has a prismatic structure of aragonite perpendicular to the shell surface and with irregular shaped cross sections. Distinct organic sheets were not observed between the crystals in M + 1, M and M - 1 layers. The (1 1 0) twins are common in all aragonite M + 2, M + 1, M and M - 1 layers, with the twin boundaries parallel to the prisms. These results for the microstructure of each layer should be considered in the discussion of the formation mechanism of the limpet shell structure. (C) 2010 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jsb.2010.04.008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

The initial formation and subsequent development of larval shells in marine bivalve, Crassostrea nippona were investigated using the FIB-TEM technique. Fourteen hours after fertilization (the trochophore stage), larvae form an incipient shell of 100-150 nm thick with a columnar contrast. Selected-area electron diffraction analysis showed a single-crystal aragonite pattern with the c-axis perpendicular to the shell surface. Plan-view TEM analysis suggested that the shell contains high density of {110} twins, which are the origin of the columnar contrast in the cross-sectional images. 72 h after fertilization (the veliger stage), the shell grows up to 1.2-1.4 mu m thick accompanying an additional granular layer between the preexisting layer and embryo to form a distinctive two-layer structure. The granular layer is also composed of aragonite crystals sharing their c-axes perpendicular to the shell surface, but the crystals are arranged with a flexible rotation around the c-axes and not restricted solely to the {110} twin relation. No evidence to suggest the existence of amorphous calcium carbonate (ACC) was found through the observation. The well-regulated crystallographic properties found in the present sample imply initial shell formation probably via a direct deposition of crystalline aragonite. (C) 2009 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jsb.2009.07.014

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Language：Japanese   Publisher：The Clay Science Society of Japan  

DOI： 10.11362/jcssjnendokagaku.48.4_158

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Language：English   Publisher：一般社団法人 日本粘土学会  

To understand the origin of its unique morphology, the structure of vermiform chlorite has been investigated. Two chlorite specimens (magnesian chamosite) were analyzed: vermicular aggregates in quartz-feldspar veins in a pelitic schist, and those grown on a quartz single-crystal surface. Both specimens show very similar textures; they are composed of pseudohexagonal chlorite plates of several tens μm in lateral size and several hundreds nm in packet thickness, stacked to form long vermicular aggregates up to several hundreds μm. Chemical analyses indicated that the two specimens have similar compositions with ^&lt;IV&gt;Al 1.2〜1.3 per 4.0 sites and Fe/(Mg+Fe) ratio of 〜0.55. XRD and EBSD indicate IIbb semi-random stacking. HRTEM shows that the stacking is considerably disordered in terms both of the layer orientation and direction of the interlayer displacement. The vermicular morphology of chlorite is probably originated from a relatively faster spiral growth along the stacking in hydrothermal fluid.

DOI： 10.11362/jcssjclayscience.14.4_155

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Early stage processes of Mg-rich chlorite (clinochlore) dissolution were examined, focusing especially on the structural modification at grain edges during dissolution. Focused ion beam transmission electron microscopy sample preparation was applied to crystals dissolved in a flow-through reaction system at pH 3.0 and 25A degrees C for 31 days. The obtained Si and Mg dissolution rates are -11.49 and -11.14 (logR, mol/(m(2)/s)), respectively, implying dissolution is non-stoichiometric. TEM-EDX analyses of dissolved samples reveal the development of 20-50-nm thick amorphous zone at an outermost rim with a chemical gradient of Mg, lower towards the solid surface, and Si enrichment in this amorphous zone. Crystalline material is partially interwoven with amorphous one at the interface between the amorphous and crystalline regions. These results indicate that the amorphous zone was produced by selective leaching of cations except for Si. Chlorite dissolution may proceed via the formation and thickening of leached layer as a by-product of release to solution of Si at slightly slower rate than Mg.

DOI： 10.1007/s00269-009-0299-x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CLAY MINERALS SOC  

Stacking disorder in celadonite, a dioctahedral mica with Fe and Mg as major octahedral cations and which generally adopts the 1M stacking sequence, was investigated mainly by using transmission electron microscopy (TEM). The selected-area electron diffraction patterns with 0kl reflections along the [100] beam direction correspond to the 1M stacking but those along the [110], [1 (1) over bar0], [010], [310], and [3 (1) over bar0] directions are frequently streaked along the [001]* direction or contain extra spots from twinned domains. Three-dimensional stacking analyses using sets of two high-resolution TEM images along different directions of the same area of one crystal indicate that all stacking faults involve only 180 degrees layer rotations. These stacking faults produce greater peaks of 0kl reflections than expected in powder X-ray diffraction (XRD) patterns. Simulation of the XRD patterns indicated that 180 degrees layer rotations occur at &gt;10% of total interlayer regions in one celadonite specimen. The interlayer region of celadonite is characterized by a near-zero ditrigonal rotation angle, a small surface corrugation of the basal oxygen plane, and a small amount of Al substitution in the tetrahedral sheets. These features suggest that there is no preference for any of the six stacking angles around the interlayer region. The abundance of 180 degrees layer rotation rather than +/- 60 degrees and +/- 120 degrees in the present specimens may be related to their ribbon-like morphologies elongated along the a axis.

DOI： 10.1346/CCMN.2008.0560602

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

A chiral tri-nuclear metal complex, Delta Delta Delta- or Lambda Lambda Lambda-[Ru(acac)(2)(taet)Ru(acac)(taet)Ru(acac)(2)] (acac = acetylacetonato and taet = tetraacetylethanato), was prepared and its monolayer behavior was investigated, leading to the conclusion that the bead-like character of the trimer was an essential factor in achieving stable two-dimensional molecular packing.

DOI： 10.1246/cl.2008.716

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：E SCHWEIZERBARTSCHE VERLAGS  

Focused ion beam (FIB) sample preparation was applied to vermiform kaolin minerals to investigate by TEM the morphological evolution and mechanisms of kaolinite-to-dickite transformation during burial diagenesis. A core sample of a K-feldspar bearing arkosic sandstone, collected from the Brent Group sediments of the Froy hydrocarbon reservoir, Norwegian continental shelf, North Sea, was studied. Two types of vermiform aggregates were analyzed: 1) porous aggregates of fine lamellar crystals or intercalations of blocky and lamellar crystals, and 2) aggregates of densely packed hexagonal crystals. Electron diffraction (ED) revealed that aggregates of the first type are composed of pure one-layer kaolinite, whereas those of the second type consist of pure two-layer dickite. The two polytypes never coexist within the same aggregate. Furthermore, ED patterns of kaolinite and dickite are almost streak free, indicating a very low density of stacking faults. These observations suggest that the kaolinite-to-dickite transition in the pores of sandstone reservoir during burial diagenesis takes place by a dissolution-precipitation process rather than by a solid-state process. Blocky kaolinite, grown epitaxially on the (001) surface of muscovite, was also found in the specimen.

DOI： 10.1127/0935-1221/2008/0020-1806

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OLDENBOURG VERLAG  

Stacking disorder is a common phenomenon in phyllosilicates but its nature is difficult to be deduced using conventional diffraction techniques. In contrast, recent investigations using high-resolution transmission electron microscopy (HRTEM) have elucidated the structure of stacking disorder in various phyllosilicates, by directly observing individual layers and stacking sequences. Furthermore, simulations of X-ray or electron diffraction patterns using the information from the HRTEM results can complement the limited analysis area in TEM and quantify the density of the stacking disorder.
Although the bonding between adjacent layers is similar, there is a significant difference in the stacking disorder between two counterparts of dioctahedral and trioctahedral 2: 1 phyllosilicates: pyrophyllite vs. talc and sudoite vs. trioctahedral chlorite. In pyrophyllite and sudoite, stacking disorder is caused mainly by two alternatives of the lateral displacement directions between the two tetrahedral sheets across the interlayer region. On the other hand, rotation of 2: 1 layer is also an origin of the stacking disorder in talc and trioctahedral chlorite. This difference is explained by the corrugation of basal oxygen planes on the dioctahedral 2: 1 layer formed by the tetrahedral tilting to enlarge trans-vacant octahedral sites.

DOI： 10.1524/zkri.2008.0004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BLACKWELL PUBLISHING  

We present a new method for the morphological analyses of minute faceted crystals by combining stereo-photogrammetric analysis of scanning electron microscope images and electron back-scattered diffraction. Two scanning electron microscope images of the same crystal, recorded at different tilt angles of the specimen stage, are used to determine the orientations of crystal edges in a specimen-fixed coordinate system. The edge orientations are converted to the indices [uvw] in the crystal system using the crystal orientation determined by electron back-scattered diffraction analysis. The Miller indices of crystal facets are derived from the indices of the edges surrounding the facets. The method is applicable to very small crystal facets. The angular error, as derived from tests using a calcite crystal of known morphology, is a few degrees.
To demonstrate the applicability of the method, the morphology of boehmite (gamma-AlOOH) precipitated from solution during the dissolution of anorthite was analyzed. The micrometre-sized boehmite crystals are surrounded by two {010} basal facets and eight equivalent side facets that can be indexed equally well as {323}, {434} or {545}. We suggest that these side facets are in fact {111}, the morphology having been modified slightly (by a few degrees) by a small extension associated with opening along (010) microcleavage planes. Tiny {140} facets are also commonly observed.

DOI： 10.1111/j.1365-2818.2007.01854.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

The stacking structures of sudoite, di-trioctahedral chlorite from two different localities are investigated by powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). XRD analyses using a Gandolfi camera revealed that the structures of both specimens are similar, corresponding to a one-layer IIbb-4 (1A) polytype. HRTEM observations indicate that the stacking sequence is characterized by a largely uniform intralayer shift of a/3 in the -X-1 direction (Xi represent the directions along the pseudohexagonal axes) and by an interlayer displacement of similar magnitude in either the -X-2 or -X-3 direction. Stacking disorder is primarily caused by the mixing of interlayer displacements in the two directions. This disorder is more common in the lath-shaped crystalline specimen from Berezovsk, Russia than in the fine platy crystalline specimen from Ottre, Belgium. DIFFaX simulations of the powder XRD patterns for this stacking model reproduced the observed features well for both specimens. The stacking configuration of these sudoite specimens is considered to be controlled by the corrugation of basal oxygen planes in the 2:1 layer and the corresponding deformation in the brucite-like interlayer sheet.

DOI： 10.2138/am.2007.2410

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CLAY MINERALS SOC  

Polytypism in gumbelite and its relationship to the fibrous or ribbon-like morphology exhibited by this Mg-rich illite were investigated by powder X-ray diffraction (XRD), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). Comparison between the XRD pattern from oriented fibers using a conventional powder diffractometer and a randomly oriented pattern using a Gandolfi camera suggested that 2M(2) is dominant but other polytypes belonging to subfamily A also exist, and that the fiber axis of gCimbelite is parallel to &lt; 1 10 &gt; in 2M(2), &lt; 1 10 &gt; in 2M(1), and &lt; 100 &gt; in 1M.TheEBSD analyses confirmed these crystallographic directions directly from individual crystals. Electron diffraction and high-resolution TEM showed that twinning and intergrowths of various polytypes including both subfamilies are common in a single crystal and that the two types of rotations [2n60 degrees and (2n+1)60 degrees] between adjacent layers are often randomly mixed at the monolayer level. The data suggest that high densities of twinning and intergrowths account for the origin of the fibrous morphology along &lt; 1 10 &gt; for 2M(1) and 2M(2) polytypes. Volume restriction in a confined vein space may also play a role.

DOI： 10.1346/CCMN.2007.0550501

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A thin film of trimethylammonium-exchanged perovskite-type niobate ((CH3)(3)NHSr2Nb3O10) was prepared by casting its exfoliated aqueous dispersion onto a glass substrate. The electric conductivity of a film (3-9 mu m thick) was measured in vacuum under the illumination of light (280 similar to 450 nm). Photocurrent raised and decayed slowly in the time range of 10(3) seconds in response to the on-and-off of an incident light. Atmospheric oxygen accelerated the decay rate of current in the dark. In the absence of oxygen, the decay curve obeyed the equation of stretched exponential relaxation (i(p) = i(p)(0) exp(-(t/tau)(beta)). From the dependence of the photocurrent on various parameters such as film thickness, light wavelength, and temperature, the observed persistent phenomena were interpreted according to the following mechanisms: (1) a free electron was photogenerated under the illumination of light most effectively when photon energy corresponded to the edge of a band gap transition; (2) the generated electrons were trapped at surface oxygen vacancies before they became conductive; and (3) a persistent current appeared through the multistep trapping-detrapping processes under the gradient of electric field. It was suggested that vacancies were produced by the elimination of lattice oxygen atoms as dianions during the acid treatment of original niobate (KSr2Nb3O10). As far as we know, the present finding is the first example of persistent photocurrents in inorganic thin films.

DOI： 10.1021/jp073380k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

A new modification of the 2 : 1 phyllosilicate layer has been discovered in annealed celaclonite, a Fe 31, Mg-rich dioctahedral mica. Plan-view diffraction patterns in TEM indicate a base-centered supercell with A = 3a and B = b, where a and b are the cell dimensions of the originat mica. Basic hOl reflections with h = 3n form an orthogonal lattice with one-layer periodicity, which is not expected for normal micas. The high-resolution TEM image along the (100) or related directions is similar to that expected from normal micas but the image along the (0 I 0) directions is completely different. From these images, it is concluded that the two tetrahedral sheets in a 2 : 1 layer are facing each other with no lateral a/3 stagger. In the proposed model that explains the high-resolution TEM images, two thirds of the spaces surrounded by two facing tetrahedral six-member rings accommodate three (Fe3+,Mg) cations and one third of the spaces are completely vacant. The (Fe3+,Mg) cations are coordinated by six or five oxygen atoms forming trigonal prisms or square pyramids, respectively.

DOI： 10.2138/am.2007.2667

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Hybrid films composed of amphiphilic molecules and clay particles were constructed by the modified Langmuir-Blodgett (LB) method. Clays used were sodium montmorillonite (denoted as mont) and synthetic smectite containing Co(II) ions in the octahedral sites (denoted as Co). Two kinds of amphiphilic molecules were useds[Ru(dC(18)bpy)( phen)(2)](ClO4)(2) (dC(18)bpy)4,4'-dioctadecyl-2,2-bipyridyl and phen = 1,10-phenanthroline) (denoted as Ru) and octadecylammonium choloride (ODAH(+) Cl- or denoted as ODAH). Three kinds of hybrid films (denoted as Rumont, Ru-Co, and ODAH-Co films) were prepared by spreading an amphiphilic molecule onto an aqueous suspension of a clay. Atomic force microscopy (AFM) analyses of the films deposited on silicon wafers indicated that closely packed films were obtained at 20 ppm for all the above three cases. Cyclic voltammetry (CV) was measured on an ITO electrode modified with a hybrid film or a monolayer film of pure Ru(II) complex salt (denoted as Ru film). The Ru( II) complexes incorporated in the Ru-mont film lost their redox activity, indicating that montmorillonite layers acted as a barrier against electron transfer. In contrast, the same complexes in the Ru-Co film were electrochemically active with the simultaneous appearance of the redox peaks due to the Co(II)/Co(III) (or Co(II)/ Co(IV))couple. The results implied that electron transfer through cobalt clay layers was possible via mediation by Co( II) ions in a clay sheet. For an aqueous solution containing nitrite ions (NO2-) at pH 3.0, a large catalytic oxidation current was observed for both the electrodes modified with the Ru-mont and Ru-Co films. The results were interpreted in terms of the mechanisms that the charge separation of an incorporated Ru(II) complex took place to produce a pair of a Ru(III) complex and an electron and that the generated Ru(III) complex was reduced by a nitrite ion before it recombined with the electron.

DOI： 10.1021/la061668f

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CLAY MINERALS SOCIETY  

The dissolution of brucite, Mg(OH)(2), on the (001) surface was investigated using in situ atomic force microscopy in solutions at near-neutral pH. Dissolution proceeded by the formation of crystallographically oriented triangular etch pits with monolayer step and expansion of the pits. The sides of the triangle are parallel to the [100], [110] and [010] directions of the brucite structure, and the orientation of lines from the center of the triangle to the three apices are along the [210], [(1) over bar 10] and [(12) over bar0] directions. This orientation may produce pit edges where OH groups coordinate to two Mg2+. Although triangular etch pits with monolayer depth formed mostly at random on the (001) surface, concentric pits penetrating several layers were also observed. Etch pits with spiral steps were rarely observed. Coalescence of the pits resulted in stranded terraces that diminished in size rapidly and formed a rounded irregular form. The step-retreat velocity around the triangular pit is 0.015-0.04 nm/s at pH 5-8. The retreat velocity around the stranded terraces was about three times more rapid than that around the triangular etch pits.

DOI： 10.1346/CCMN.2006.0540506

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

Stacking structure in disordered talc, Mg3Si4O10(OH)(2), has been investigated by using high-resolution transmission electron microscopy (HRTEM) and by comparison between experimental and simulated powder X-ray diffraction (XRD) patterns. The talc specimen investigated was massive aggregates of fine platy crystals from the Shirakashi mine, Nagasaki-Prefecture, Japan, formed from regional metamorphism. HRTEM observations revealed that the orientation of the 2:1 layer, which is described by the direction of the lateral shift of a/3 from the lower tetrahedral sheet to the upper tetrahedral sheet within the 2:1 layer (intralayer shift), is almost completely disordered. In contrast, lateral displacement between the adjacent tetrahedral sheets across the interlayer region (interlayer displacement) is relatively ordered. The interlayer displacement parallel to the intralayer shift in lower or upper 2:1 layers tends to be avoided.
A Gandolfi camera was used to record XRD patterns from a small fragment of the aggregates, to avoid preferred orientation and artifacts in stacking sequence by grinding. XRD patterns were simulated using the DIFFaX program and compared with experimental patterns. The experimental pattern from hk = 02, 11, and 11 reciprocal lattice rows is explained by a mixture of the stacking sequence with almost random directions of intralayer shift and a small amount of 1A dominant stacking sequence. The peak profiles for the reflections indexed with 20l, 13l, or 13l are reproduced by considering their variance, and a slightly different interlayer displacement from that reported in talc-1A.

DOI： 10.2138/am.2006.2196

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

Stacking structures in pyrophyllite, Al2Si4O10(OH)(2), were investigated mainly by using high-resolution transmission electron microscopy (HRTEM). The specimens examined were large lath-shaped crystals (Berosovska, Urals, Russia) and massive aggregates of fine platy crystals (Nohwa, southwest Korea). Both specimens showed powder X-ray diffraction (XRD) patterns similar to those reported previously as the 2M polytype. The common stacking sequence in the two specimens is not monoclinic with two-layer periodicity as previously reported, but a uniform orientation of the 2:1 layers and near complete disorder of two alternative directions of interlayer displacement, i.e., lateral displacement between the two tetrahedral sheets across an interlayer region. The directions of interlayer displacement are about +/- 2 pi/3 from that of the intralayer shift (lateral displacement between the two tetrahedral sheets within a 2:1 layer). Simulation of powder XRD patterns by this stacking model closely approximates the experimental pattern. Elongation of the lath-shaped Berosovska crystals corresponds to the direction of the intralayer shift, as seen in illite-1M.
2:1 layers with different orientations, and interlayer displacement almost parallel to the intralayer shift, were occasionally observed as stacking faults. Such disorder occurs more frequently in the massive Nohwa specimen than in the Berosovska specimen. Sub-micrometer domains of the 2M stacking sequence with regular alternation of the two directions of interlayer displacement were found in the Nohwa specimen.

DOI： 10.2138/am.2006.1997

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Hypervelocity impact experiments are carried out with alumina ceramic targets at impact velocities of 2-4 km/s. The fractal dimension (or roughness exponent) of fragment surfaces is estimated by two different methods (different length scales). One is a divider method (large scale) and the other is a gas-absorption one (small scale). The obtained fractal dimensions are different: similar to 2.2-2.4 for larger scale and similar to 2.5-2.7 for smaller scale. These values are regardless of the degree of fragmentation. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.pss.2005.09.002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

Morphology of kaolinite crystals with high-crystallinity (Keokuk, Iowa) has been investigated by electron back-scattered diffraction (EBSD) and high-resolution scanning electron microscopy (SEM). EBSD patterns from the specimen generally correspond to those expected from ordered kaolinite. Elongated hexagonal crystals always show the a-axis parallel to the elongated direction. The side-facets of these crystals are in parallel to the c-axis, which is inclined by about 15 degrees from the normal to the basal plane. The Miller indices of the side-facets are exactly +/-(110), +/-(1 (1) over bar0), and +/-(0 10). A facet indexed as +/-(1 (3) over bar0) is developed in some crystals. These morphological characteristics must be reflected in the ordered stacking sequences (the position of the octahedral vacancy site and the direction of the interlayer shift) of the Keokuk kaolinite. Inversely, the crystallinity of individual kaolinite grains may be evaluated from their morphology in a SEM. The feasibility to discriminate the enantiomers in kaolinite using EBSD is also described.

DOI： 10.2138/am.2005.1928

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A hybrid film of layered niobate and an organic amphiphile was prepared by the Langmuir-Blodgett (LB) method. Trimethylammonium-exchanged perovskite-type niobates ((CH3)(3)NHSr2Nb3O10) were exfoliative to form an aqueous suspension. A monolayer of octadecylamine was produced on such an aqueous dispersion as a template for a hybrid film. A hybrid film was transferred as a Y-type LB film onto a hydrophilic glass plate or an ITO substrate. The structure of a deposited film was investigated with X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and atomic force microscopy (AFM) measurements, indicating a layer-by-layer structure with a single or double sheet of niobate as an inorganic composite. From the cyclic voltammogram on an ITO electrode modified with the Y-type 10 layered film, the lower edge of the conduction band of a niobate layer was determined to be - 0.6 V (vs Ag/AgCl). ac impedance and dc measurements were carried out on 1, 5, and 10-layered LB films (2 mm (electrode spacing) x 8 mm (width)) with aluminum electrodes. The freshly deposited samples behaved as an insulator under the illumination of 280 nm light (2.04 x 10(16) quanta s(-1)). Photoconductivities appeared, however, when they were preirradiated with a 150 W Xe lamp (ca. 2 x 10(18) quanta s(-1)) for 0.5-8.5 h. The process was denoted as photomodification. From the FT-IR and XRD results, it was deduced that the photomodification of LB films caused the decomposition of organic templates (octadecylammonium) accompanied by the collapse of layer-by-layer structures. dc analyses on the 5- and 10-layered films after photomodification also showed that they behaved as a photosemiconductor under UV light illumination.

DOI： 10.1021/jp0505476

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

By measuring the photoconductivity of hybrid LB films of exfoliative layered niobate and octadecylamine, it was evidenced that the film underwent a transition from an insulator to a photosemiconductor during photo-modification treatment by UV fight, which was rationalized in terms of the direct contact of inorganic nanosheets achieved by the elimination of organic layers.

DOI： 10.1039/b419064e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

H-2 generation during mechanochemical treatment of kaolinite by dry grinding was examined by X-ray diffraction analysis, Fourier transform infrared spectroscopy, and BET surface area measurement. The H-2 concentration in the mill pot, measured by gas chromatography, increased with grinding time up to a maximum concentration of 156 ppm (0.35 mumol) after 600 min. This H-2 generation is considered to occur as a result of three processes: (1) structural destruction characterized by the delamination and loss of hydroxyl groups as a result of dry grinding, (2) transformation of liberated hydroxyls into water molecules by mechanochemical effects such as prototropy, and (3) H-2 generation through reaction between surface water molecules and mechanoradicals created by the rupture of Si-O or Al-O-Si bonds. Although the surface area plateaued after 240 min grinding, the H-2 concentration continued to increase, indicating that surface mechanoradicals are created during this later grinding stage. Thus, H-2 generation can be used as an indicator of mechanoradical formation during mechanochemical treatment. (C) 2004 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jcis.2004.02.014

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER-VERLAG  

To understand the fundamental chemical processes of fluid-rock interaction during the pulverization of quartz grains in fault zones, quartz grains were crushed within pure water. The crushing experiments were performed batch style using a shaking apparatus. The crushing process induced a decrease in pH and an increase in hydrogen gas with increased shaking duration. The amount of hydrogen ions generated was five times larger than that of the hydrogen gas, which was consistent with the amount of Si radicals estimated from electron spin resonance measurements by Hochstrasser and Antonini (1972). This indicates that hydrogen gas was generated by consuming most of the Si radicals. The generation of hydrogen ions was most likely related to the presence of silanols on the newly formed mineral surface, implying a change of proton activities in the fluid after pulverization of quartz.

DOI： 10.1007/s00269-004-0382-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TERRA SCIENTIFIC PUBL CO  

The mechanism of hydrogen generation during the mechanochemical treatment of biotite was examined by grinding experiments using a ball mil in H2O or D2O as a grinding media. From the linear relationship between the amount of generated hydrogen and the increase of the surface area of ground powders, the hydrogen productivity of biotite is estimated to be 0.036 mu mol/m, which agrees with the previous results in spite of the difference in the grinding conditions. D-2 analyses by a mass spectrometry indicate that the produced amount of D-2 accounts for only 10% of the total hydrogen and that more than 90% of hydrogen takes a form of a mixture of HD and H-2. The observed isotope distribution clearly indicates that hydroxyls within the crystal structure can be a major source for the generation of hydrogen. Hydrogen generation originated from hydroxyls may indicate the higher hydrogen productivity of phyllosilicates than those of quartz and alkali feldspar.

DOI： 10.1186/BF03353346

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Hydrogen generation was investigated by grinding quartz powder in pH- and ionic strength-controlled liquid media. The effect of ionic strength on hydrogen generation was negligible, while the decrease of generated hydrogen in the acidic pH region (&gt;5.0) was observed. The mechanism of these mechanochemical reactions was discussed.

DOI： 10.1246/bcsj.76.2153

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Granite and single crystals of quartz, alkali feldspar, biotite and muscovite are ground in pH-controlled and pure water solutions using a ball mill at ambient condition to examine the production of H-2. The amount of H-2 generated by grinding is linearly related with the surface area of ground samples. The slope of the straight line indicates H-2 productivity of each mineral: 3.9 x 10(-3) mumol/m(2) (quartz); 1.0 x 10(-3) mumol/m(2) (alkali feldspar); 3.6 x 10(-2) mumol/m(2) (biotite); 2.2 x 10(-2) mumol/m(2) (muscovite); 4.5 x 10(-3) mumol/m(2) (granite). High productivity of biotite and muscovite is probably related to the existence of hydroxyls in their crystal structures. Interestingly, H-2 production did not depend on the pH of the solution in the case of biotite and granite, while comparisons between fluid acidity and H-2 concentration on several active faults suggest that anomalously high H-2 is commonly observed at relatively acidic water springs. This correlation may be explained by locally high abundance of phyllosilicates.

DOI： 10.1029/2003GL018252

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TERRA SCIENTIFIC PUBL CO  

A new model for growth of plastic shear zone is proposed based on the basis of a theory of fluid dynamics coupled with a rheological constitutive function, and is applied to a natural shear zone. Mylonite, ultramylonite and other ductile fault rocks are well known to deform in a plastic flow regime. The rheological behavior of these kinds of rocks has been well documented as a non-linear viscous body, which is empirically described as gamma = Atau'' exp(-Q/RT), where : strain rate, tau: shear stress, Q: activation energy, R: universal gas constant, tau: absolute temperature, and A and n are constants. Strain rate- and temperature-dependent viscosity is obtained by differentiating the equation, and simplified by substituting n = 1. Then, substitution of the equation into a diffusion equation, delta = 4rootvt, derives an equation delta = 4[t/p] . A exp(-Q/RT)(1/2), where delta: thickness of active layer of viscous deformation, v: kinematic viscosity, and p: density. The duration of creep deformation along the ancient plastic shear zone (thickness: 0.076 m) is estimated to be around 760 s, in a temperature range from 300 to 500degreesC. This estimation is rather good agreement with intermittent creep during inter-seismic period, than steady state creep or co-seismic slip.

DOI： 10.1186/BF03353321

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Language：Japanese   Publisher：公益社団法人 東京地学協会  

The region from Sakhalin in Russia to the eastern margin of the Japan Sea has been regarded as a convergent plate boundary zone between the Eurasia and the North America Plates because large earthquakes and active crustal movements are prominent in this zone. These activities along the eastern margin of the Japan Sea to southern Sakhalin are almost consistent with the expected relative plate motion deduced from the Euler pole which is estimated from the magnetic anomaly lineations in the Atlantic Ocean, but the modern tectonic aspect in northern Sakhalin is inconsistent; &lt;I&gt;e.g.&lt;/I&gt;, 1995 Neftegorsk Earthquake is one of the typical events.&lt;BR&gt;As a result of a structural and tectonic study in northern Sakhalin, the NE-SW compressive tectonic feature since the Late Miocene was clarified. In the northernmost area of the Schmidt Peninsula, the early Cretaceous ophiolite thrusts upon the Late Cretaceous sedimentary rocks. The ophiolite has an overturned sequence: serpentinites, gabbros, basaltic rocks, and hemipelagic sediments in descending order. The Cretaceous sediments form a map-scale and NW vergent synclinorium. All the deformation structures in outcrop scale, such as micro-folds, minor reverse and normal faults, axial plane cleavages and bedding slips, are consistent with a large scale folding. These structural relationships suggest only one event of deformation, which appears to be linked to overthrusting of the ophiolitic rocks.&lt;BR&gt;A structural investigation of the southeastern part of the Schmidt Peninsula revealed that the Middle Miocene sediments composed of siltstone and sandstone are folded with wavelength of several tens to several hundred meters. Their fold axes trend in the NW direction, which indicates that deformation under the NE compression is the same as the deformation in the northernmost area. The thickness of sedimentary layers are constant everywhere in folding. This fact indicates that the timing of the deformation is after sedimentation, that is, after the Middle Miocene. This deformation event is consistent with modern activity in northern Sakhalin. Therefore, the modern tectonic framework might have started in the Late Miocene time.&lt;BR&gt;A plate tectonic model indicates that the modern relative motion between the Eurasia and the North America Plate started at about 11 m. y. ago. The Late Miocene onset of the modern tectonic framework in northern Sakhalin occurred at almost the same time. The most reliable model to explain the discrepancy of sense of movement from the Eurasia-North America retative motion, may be the &amp;ldquo;extrusion&amp;rdquo; of the Okhotsk Block toward the Pacific Ocean. The dextral extrusion boundary in northern Sakhalin may be traced along theeastern coast of Sakhalin to the northern edge of the Kuril Basin, where active seismicityhas been observed although a detailed study of focal mechanisms and other tectonic aspects is needed in the future.

DOI： 10.5026/jgeography.109.2_235

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Language：Japanese   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2010.0.31.0

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Language：Japanese   Publisher：日本粘土学会  

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DOI： 10.11362/cssj2.51.0.100.0

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Language：Japanese   Publisher：The Geological Society of Japan  

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Language：Japanese   Publisher：日本粘土学会  

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Language：Japanese   Publisher：海洋出版  

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Language：Japanese   Publisher：日本粘土学会  

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