Geometry and Internal Structures of Flexural Folds (Ⅰ) Folding of a Single Competent Layer Enclosed in Thick Incompetent Layer

Some problems on folding of a single competent layer enclosed in thick incompetent layer, with regard to the variation in competency difference between the related rocks, have been examined on natural flexural folds, i. e., folds of quartz-rich layers in pelitic schist in the Kune district and the Oboke district, folds of quartz-rich layers in psammitic schist in the Oboke district, and folds of psammitic schist in pelitic schist in the Oboke district. Shape and orientation of the strain ellipsoid of mean strain of small domain in the Oboke and the Kune district, at the time when the buckle folding of competent layers and the cleaving (the formation of strain-slip cleavage) of incompetent matrix in that domain occurred, have been determined. The strain-slip cleavage in the incompetent matrix is correlated with the plane normal to the direction of maximum shortening, i. e., the principal plane XY of the mean strain ellipsoid. Geometric relationships between the strain ellipsoid of mean strain of a domain and geometric elements of buckle folds have been examined, especially where the enveloping surfaces of folded competent layers are inclined at angles of between 50° and 60° to the principal plane XY. At the initial stage of folding the axial surface shows a tendency to be normal to the layer being folded. For some folds the axial surfaces are completely rotated toward the principal plane XY when the interlimb angle becomes 90°-100°, but for some other folds they remain normal to the layer even when the interlimb angle becomes 700-80°. When the interlimb angle becomes smaller than 70-80°, the axial surfaces of all folds tend to rotate toward the principal plane XY. Although geometric relationship between the fold axes and the mean strain ellipsoid has not been strictly determined, the former does not appear to lie on the principal plane XY. The intensity of folding of competent layers, which is estimated by interlimb angle, is maximum for the layers parallel to the schistosity of the incompetent matrix and to the principal axis Z, and minimum for those normal to the schistosity and parallel to the axis Z, that showing the competency difference between different directions in the incompetent matrix, that is, the maximum competency in a direction parallel to the schistosity and the minimum in a direction normal to it. It has been clarified that for the folds of quartz-rich layers in pelitic schist of the Kune district and the Oboke district and those in psammitic schist of the Oboke district a linear relationship exists between the length of arc (L) and the thickness of the quartz-rich layer (T). In the former cases, the average L/T ratios are 14.9 (Kune) and 16.2 (Oboke), and the minimum L/T ratios are 9.1 and 11.6, while in the latter case the average L/T ratio is 11.6 and the minimum L/T ratio 5.8, respectively. Folds of psammitic layers in pelitic schist show frequently L/T ratios smaller than 1.00. On the assumption that during the folding pelitic schist, psammitic schist and quartz-rich layer behaved mechanically as Newtonian substance, the ratios of viscosity coefficient between those rocks have been esti-mated by using the average L/T ratios according to the wavelength equation of BIOT (1961). In the Oboke district, the viscosity ratio between the quartz-rich layer and the psammitic schist is ca. 38, that between the quartz-rich layer and the pelitic schist ca. 102, and that between the psammitic schist and the pelitic schist ca. 3 (indirectly estimated). In the Kune district, the viscosity ratio between the quart-rich layer and the pelitic schist is ca. 80. The relationship between the mechanisms of buckle folding and the internal structures, between the folding mechanisms and the viscosity ratios of the related rocks and between the folding mechanisms and the orientational relation of the buckled layer to the mean strain ellipsoid of the domain concerned have also been examined. Internal structure of buckle fold appears to be commonly characterized by the cleavage which is correlated with the principal plane XY of mean strain ellipsoid at any position of the fold. When buckled competent layer is a schistose rock, the cleavage is referred to the type of strain-slip cleavage, while for non-schistose rock it is referred to the type of flow cleavage. The strain pictures developed during the buckle folding of competent layers which arc parallel or subparallel to the principal axis Y (the intermediate axis = constant) have been classified into the following five types; Type I — the neutral axis is located at or near the middle part of fold knee, and the part of no-distortion is further developed at the inflection point and on the outermost side of the limbs. The principal axes X (the maximum extension axis) and Z(the maximum contraction axis) arc oriented normal to the fold axis. Type II — the neutral axis is developed at the outermost part of fold knee, and the part of no-distortion is rarely developed on the limbs. The principal axes X and Z are oriented normal to the fold axis, and the principal axis X is radially arranged through the fold. Type III — the neutral axis is not developed within the layer. The principal axes X and Z are oriented normal to the fold axis, though at the outermost part of fold knee X = Y. The principal axis X is radially arranged through the fold. Type IV— the neutral axis is not developed within the layer. At any position of the fold the mean strain ellipsoid is of the triaxial type. The principal axes X and Z arc oriented normal to the fold axis. The principal axis X is radially arranged through the fold. Type V —although the strain picture of this type may be essentially the same as that of Type IV, the angle β (angular deviation of the principal axis X beween both limbs) for the former is much smaller than that for the latter. The change of the strain picture from Type I to Type V corresponds to the decrease of the angle β. The strain pictures of Type I, Type II, Type III, Type IV and Type V are never the end member. The folds of quartz-rich layers in politic schist of the Kune district show the strain pictures of Type I, Type II and Type III, while those in psammitic schist show the strain pictures of Type II, Type III and Type IV. The folds of psammitic layers in pelitic schist show the strain picture of Type V. A definite relationship exists between the mechanisms of folding and the viscosity ratios of the related rocks, that is, the change of the strain picture from Type I to Type V corresponds to the decrease in the viscosity ratio, that showing a good agreement with RAMBERG'S theory (1964). Namely, the decrease of viscosity ratio of the related rocks corresponds to the increase of distance of between the neutral axis and the bottom surface of fold knee of the competent layer, and to the decrease of the angle β, when compared between the folds with the same inter-limb angle and the same initial thickness of layer. It has been pointed out that, if any fold is characterized the fan-like arrangement of cleavage with downward convergence, buckling instability played in general the by important role in the development of the fold. The nature of change of layer-thickness due to buckling has also been examined. For folds which show orthorhombic or near orthorhombic symmetry and larger interlimb angles, the competent layers show generally a tendency to be thickened at all positions of the folds and the amount of thickening appears to be maximum at the fold knee and minimum at the inflection point. The nature of change of layer-thickness due to buckling appears to be closely related to the type of strain picture (Type I to Type V) which is controlled by the viscosity ratio of the related rocks: with respect to the whole amount of layer shortening, the amount of layer thickening at the fold knee and the inflection point, and the difference in the amount of layer thickening between these two positions, Type I <Type II<Type III <Type IV <Type V, when compared between the folds with the same interlimb angle. Roughly speaking, the layer shortening due to the folding (interlimb angle = ca. 65°), which is characterized by the formation of the strain picture of Type I, may be less than ca. 10 per cent. That due to the folding for the strain picture of Type II may be between ca. 10 per cent and ca. 15 per cent. And, that due to the folding for the strain picture of Type IV—Type V may be larger than ca. 15 per Cent. For the fold of competent layer, therefore, the present length of arc is not always equal to the initial fold wavelength. From the measurement of the layer shortening for the folds of quartz-rich layers in the Kune district and the Oboke district, the average L/T ratios and the viscosity ratios between the related rocks have been re-estimated

Geotechnical Properties of Kanto Alluvial Soils based on Geochemical Survey

Chemical properties of pore water in soils have a great influence on interparticle bonding among clayey particles and, as a result, not only on their soil structure but also on their geotechnical properties. In this study, we analyzed ionic compositions in pore water extracted from alluvial soils deposited under different sedimentary environments in Kanto lowland area, Japan, and investigated the effect of the chemical compositions of pore water on the geotechnical properties such as compressibility and sensitivity. The following results were obtained: The ion concentrations of pore water measured by different extraction methods showed that the concentration of Na+ by the dilution method was higher than that by the centrifugation method, while the concentrations of Ca2+, Cl- and SO42- by the dilution method are significantly smaller than those by centrifugation method. The centrifugation method was recommended for evaluating geochemistry of the soils since the rotation speeds in the centrifugation method did not significantly affect the pore-water compositions. The geotechnical properties were highly related to the ion concentrations of pore water. Higher compression index and sensitivity were observed for the alluvial soils with higher monovalent/divalent ion ratio. In addition, more strong dependency of monovalent/divalent ion ratio on geotechnical properties was obtained for the alluvial soils with plasticity index larger than 30

Three-Dimensional Fabric Analysis for Anisotropic Material Using Multi-Directional Scanning Line -Application to X-ray CT Image-* 1

In microscopic analysis, materials are characterized by a three-dimensional (3D) microstructure which is composed of constituent elements such as pores, voids and cracks. A material&apos;s mechanical and hydrological properties are strongly dependent on its microstructure. In order to discuss the mechanics of geomaterials on a microstructural level, detailed information on their 3D microstructure is required. X-ray computed tomography is a powerful non-destructive method for determining the microstructure, however it can be difficult to determine a material&apos;s microstructure from the reconstructed 3D image. We successfully evaluated the 3D microstructural anisotropy of porous and fibrous materials using a multi-directional scanning line method that employs straightforward image analysis, and its results were visualized using stereonet projection

Investigation of meson masses for real and imaginary chemical potential

We investigate chemical-potential ($\mu$) and temperature ($T$) dependence of scalar and pseudo-scalar meson masses for both real and imaginary $\mu$, using the Polyakov-loop extended Nambu--Jona-Lasinio (PNJL) model with three-flavor quarks. A three-flavor phase diagram is drawn in $\mu^2$-$T$ plane where positive (negative) $\mu^2$ corresponds to positive (imaginary) $\mu$. A critical surface is plotted as a function of light- and strange-quark current mass and $\mu^2$. We show that $\mu$-dependence of the six-quark Kobayashi-Maskawa-'t Hooft (KMT) determinant interaction originated in $U_\mathrm{A}(1)$ anomaly can be determined from lattice QCD data on $\eta'$ meson mass around $\mu =0$ and $\mu = i \pi T/3$ with $T$ slightly above the critical temperature at $\mu=0$ where the chiral symmetry is restored at $\mu=0$ but broken at $\mu =i \pi T/3$, if it is measured in future.Comment: 13 pages, 12 figure

Feasibility study of immediate pharyngeal cooling initiation in cardiac arrest patients after arrival at the emergency room

AIM: Cooling the pharynx and upper oesophagus would be more advantageous for rapid induction of therapeutic hypothermia since the carotid arteries run in their vicinity. The aim of this study was to determine the effects of pharyngeal cooling on brain temperature and the safety and feasibility for patients under resuscitation. METHODS: Witnessed non-traumatic cardiac arrest patients (n=108) were randomized to receive standard care with (n=53) or without pharyngeal cooling (n=55). In the emergency room, pharyngeal cooling was initiated before or shortly after return of spontaneous circulation by perfusing physiological saline (5 °C) into a pharyngeal cuff for 120 min. RESULTS: There was a significant decrease in tympanic temperature at 40 min after arrival (P=0.02) with a maximum difference between the groups at 120 min (32.9 ± 1.2°C, pharyngeal cooling group vs. 34.1 ± 1.3°C, control group; P<0.001). The return of spontaneous circulation (70% vs. 65%, P=0.63) and rearrest (38% vs. 47%, P=0.45) rates were not significantly different based on the initiation of pharyngeal cooling. No post-treatment mechanical or cold-related injury was observed on the pharyngeal epithelium by macroscopic observation. The thrombocytopaenia incidence was lower in the pharyngeal cooling group (P=0.001) during the 3-day period after arrival. The cumulative survival rate at 1 month was not significantly different between the two groups. CONCLUSIONS: Initiation of pharyngeal cooling before or immediately after the return of spontaneous circulation is safe and feasible. Pharyngeal cooling can rapidly decrease tympanic temperature without adverse effects on circulation or the pharyngeal epithelium

A micromechanical model for brittle failure of rock and its relation to crack growth observed in trixial compression tests of granite

A micromechanics-based continuum damage model for brittle failure of rock is proposed to provide a numerical tool for analyzing not only the macro-scale mechanical responses of rock under compression such as strength, but also microscopic events, which take place in association with inelastic deformation. Special emphasis is placed on predicting numerically the changes in crack length and crack density during inelastic deformation terminating in brittle failure. Only two parameters, typical size and fracture toughness, are involved in the present model. These can be determined by reading the stress at an initial damage point C′ on a stress–volumetric strain curve. The present model seriously underestimates the dilatational volumetric strains observed experimentally in triaxial tests of Inada granite. This is probably because a new micromechanism starts working in the final stage. The peak (failure) stress obtained numerically is in good accordance with the one observed in triaxial compression tests under a confining pressure higher than, say, 10 MPa. In the case of uniaxial tests in particular, the numerical model seriously overestimates the uniaxial strength. A major tension crack grows through the sample parallel to the axial direction in uniaxial tests, once the crack attains a critical length, while failure occurs in triaxial tests under confining pressures higher than 10 MPa only when the microcrack density is high enough. The overestimation probably reflects such a difference in the micromechanism leading to failure (peak stress). In spite of these difficulties, it can still be said that the proposed model has a chance of providing a sound basis for predicting crack growth, such as crack length and crack density, with sufficient accuracy. To improve the model, we must take into account the real micromechanism of crack growth effective in the final stage and the change in the number density of microcracks ρ during the loading process