A 2.5-D time-domain elastodynamic equation for a general anisotropic medium     

Hiroshi Takenaka  Brian L. N. Kennett 《Geophysical Journal International》1996,127(2):F1-F4

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Origin of layering in cumulate gabbros in the Oman ophiolite: Insights from magnetic susceptibility measurements in the Wadi Sadm area     

Kiichiro  Kawamura  Takahiro  Hosono  Huda Mohamed  Allawati  Yujiro  Ogawa  Hidetsugu  Taniguchi 《Island Arc》2005,14(4):564-570

Abstract   Magnetic susceptibility and the anisotropy of magnetic susceptibility were measured on an 800-cm-thick succession of cumulate gabbro in the Sadm area of the Oman ophiolite. The section contained three distinct cumulate units. The susceptibility tends to decrease upward in each from a melanocratic layer (several tens of centimeters thick) to a leucocratic layer (a few meters thick). The susceptibility decreases in accordance with the decreasing number of magnetite grains, which are the alteration product mainly of olivine minerals. This suggests the cyclic downward accumulation of olivine in the cumulate gabbro. The apparent strain deduced from the patterns of magnetic and grain fabrics was the result mostly of simple shear, so that the layering of gabbro is understood to be formed primarily by a crystal cumulus process followed by simple shear deformation.  相似文献   

Transpressional tectonics of the Mineoka Ophiolite Belt in a trench–trench–trench-type triple junction, Boso Peninsula, Japan     

Ryota  Mori  Yujiro  Ogawa 《Island Arc》2005,14(4):571-581

Abstract   Structures developed in metamorphic and plutonic blocks that occur as knockers in the Mineoka Ophiolite Belt in the Boso Peninsula, central Japan, were analyzed. The aim was to understand the incorporation processes of blocks of metamorphic and plutonic rocks with an arc signature into the serpentinite mélange of the Mineoka Ophiolite Belt in relation to changes in metamorphic conditions during emplacement. Several stages of deformation during retrogressive metamorphism were identified: the first faulting stage had two substage shearing events (mylonitization) under ductile conditions inside the crystalline blocks in relatively deeper levels; and the second stage had brittle faulting and brecciation along the boundaries between the host serpentinite bodies in relatively shallower levels (zeolite facies). The first deformation occurred during uplift before emplacement. The blocks were intensively sheared by the first deformation event, and developed numerous shear planes with spacing of a few centimeters. The displacement and width of each shear plane were a few centimeters and a few millimeters, respectively, at most. In contrast, the fault zone of the second shearing stage reached a few meters in width and developed during emplacement of the Mineoka Ophiolite. Both stages occurred under a right-lateral transpressional regime, in which thrust-faulting was associated with strike-slip faulting. Such displacement on an outcrop scale is consistent with the present tectonics of the Mineoka Belt. This implies that the same tectonic stress has been operating in the Boso trench–trench–trench-type triple junction area in the northwest corner of the Pacific since the emplacement of the Mineoka Ophiolite. The Mineoka Ophiolite Belt must have worked as a forearc sliver fault during the formation of a Neogene accretionary prism further south.  相似文献   

Antiferromagnetic transition of fayalite under high pressure studied by Mössbauer spectroscopy     

Mitsuhiko Hayashi  Ichiro Tamura  Osamu Shimomura  Hiroshi Sawamoto  Haruki Kawamura 《Physics and Chemistry of Minerals》1987,14(4):341-344

Néel temperature (Tm _N of α-Fe₂SiO₄ (fayalite) was measured as a function of pressure by means of Mössbauer spectroscopy in the pressure range 0–16 Gpa. High pressure was generated using a clamp-type miniature diamond anvil cell which was inserted into a cryostat. The Néel temperature increased linearly with increasing pressure at a rate of dT _N /dp=2.2±0.2 K/GPa. The result is discussed on the basis of the model proposed for the magnetic structure of fayalite by Santoro et al. (1966). The observed dT _N /dp suggests that the superexchange interactions vary as the ?10/3 power of the volume while the volume dependence of the direct exchange interactions is positive and small.  相似文献   

Kinetics of reactions between aqueous sulfates and sulfides in hydrothermal systems   总被引：1，自引：0，他引：1  

Hiroshi Ohmoto  Antonio C. Lasaga 《Geochimica et cosmochimica acta》1982,46(10):1727-1745

The rates of chemical reactions between aqueous sulfates and sulfides are essentially identical to sulfur isotopic exchange rates between them, because both the chemical and isotopic reactions involve simultaneous oxidation of sulfide-sulfur atoms and reduction of sulfate-sulfur. The rate of reaction can be expressed as a second order rate law: R = k·[∑SO₄^2?]·[∑S^2?], where R is the overall rate, k is the rate constant and [∑SO₄^2?] and [∑S^2?] are molal concentrations. We have computed the rate constants from the available experimental data on the partial exchange of sulfur isotopes between aqueous sulfates and sulfides using the rate law established by us: $\text{ln(}\text{α}{}^{\mathrm{e}}\text{? α}\text{α}{}^{\mathrm{e}}\text{? α}{}^0\text{) = ? kt([∑SO}{}_4{}^{\mathrm{2?}}\text{] + [∑S}{}^{\mathrm{2?}}\text{])}$, where t is time and α⁰, α, and α^e are, respectively, the fractionation factors at t = 0 (the initial condition), at the end of experiment, and at equilibrium. The equilibrium fractionation factor can be expressed as: $\text{1000 ln α}{}^{\mathrm{e}}\text{=}\text{6.463 × 10}{}^6\text{T}{}^2\text{+ 0.56 (±.5)}$ (T in Kelvin).The rate constants are strongly dependent on T and pH, but not in as simple a manner as suggested by Igumnov (1976). Our rate constants in Na-bearing hydrothermal solutions decrease by 1 order of magnitude with an increase in pH by 1 unit at pH's less than ~3, remain constant in the pH range of ~4 to ~7, and again decrease at pH >7. The activation energy for the reaction also depends on pH: 18.4 ± 1 kcal/mole at pH = 2, 29.6 ± 1 kcal/mole at pH = 4 to 7, and between 40 and 47 kcal/mole at pH around 9. The observed pH dependence of the rate constant and of the activation energy can be best explained by a model involving thiosulfate molecules as reaction intermediates, in which the intramolecular exchange of sulfur atoms in thiosulfates becomes the rate determining step.The rate constants obtained in this study were used to compute the changes in the isotopic fractionation factors between aqueous sulfates and sulfides during cooling of fluids. Comparisons with data of coexisting sulfate-sulfide minerals in hydrothermal deposits, suggest that simple cooling was not a likely mechanism for coprecipitation of sulfate and sulfide minerals at temperatures below 350°C. Mixing of sulfide-rich solutions with sulfate-rich solutions at or near the depositional sites is a more reasonable process for explaining the observed fractionation.The degree of attainment of chemical equilibrium between aqueous sulfates and sulfides in a hydrothermal system, and the applicability of a_O2-pH type diagrams to mineral deposits, depends on the ∑S content and the thermal history of the fluid, which in turn is controlled by the flow rate and the thermal gradient in the system.The rates of sulfate reduction by non-bacterial processes involving a variety of reductants are also dependent on T, pH, [∑SO₄^2?], and [∑S^2?], and appear to be fast enough to become geochemically important at temperatures above about 200°C.  相似文献   

High temperature heating of the Allende meteorite     

Kenji Notsu  Naoki Onuma  Norimasa Nishida  Hiroshi Nagasawa 《Geochimica et cosmochimica acta》1978,42(6):903-907

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Resonance capacity method for earthquake response analysis of hysteretic structures     

Minoru Yamada  Hiroshi Kawamura 《地震工程与结构动力学》1980,8(4):299-313

The Resonance Capacity Method is proposed for the earthquake response analysis of hysteretic structures. Resonance Capacity is a physical quantity of structures which is related to the hysteretic energy absorbed by structures in one cycle and is equated to the acceleration, velocity and displacement amplitudes α₀, d₀ and d₀ of earthquake ground motions at resonance.¹ According to the idealized trapezoidal approximation of earthquake ground motions in the logarithmic period–velocity plane as proposed by Veletsos and Newmark,⁸ the Resonance Capacity property applies in each period range, short, medium and long, where α₀, v₀ and d₀ respectively are approximately constant. In the medium range of periods, the energy dissipated in hysteretic loops and the deformation amplitudes of a single-degree system with elasto–plastic force–deformation relationships are calculated for the case of El Centro 1940, 18 May earthquake, by this Resonance Capacity Method. The result is compared with results from conventional numerical response analyses obtained by Berg and Thomaides,¹⁴ Kato and Akiyama¹² and Veletsos and Newmark,⁸ and the general agreement is seen to be good. Therefore, it may be possible to apply this Resonance Capacity Method over the entire range of periods. By means of this method the earthquake response analysis of hysteretic systems can be performed easily, and the hysteretic energy and fatigue characteristics of structures may be taken into account directly, up to the point of fracture.  相似文献   

Trace element in igneous petrology | C.J. Allègre and S.R. Hart (Editors), 1978. A Volume in Memory of Paul W. Gast. Developments in Petrology, 5. Elsevier,Amsterdam, 272 pp., Dfl. 121.00, $ 49.95     

Hiroshi Nagasawa 《Earth》1979,15(1):79-80

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Undrained dynamic-loading ring-shear apparatus and its application to landslide dynamics   总被引：26，自引：17，他引：9  

Kyoji Sassa  Hiroshi Fukuoka  Gonghui Wang  Naohide Ishikawa 《Landslides》2004,1(1):7-19

Landslides are gravitational mass movements of rock, debris or earth. Some move very slowly, thus conforming to the field of statics, but some move rapidly. Study of the initiation and motion of rapid landslides needs to develop Landslide Dynamics involving dynamic loading and dynamic generation/dissipation of excess pore-water pressure. New developments in science can be facilitated by new technological advances. This study aimed to develop a new apparatus that can geotechnically simulate the formation of the shear zone and the following long and rapid shear displacement that occurs in high-velocity landslides. Professor K. Sassa and his colleagues at DPRI (Disaster Prevention Research Institute), Kyoto University, have worked to develop an undrained dynamic-loading ring-shear apparatus for this purpose. A series of different types of apparatus (DPRI-3, 4, 5, 6, 7) have been developed from 1992 to the present. This paper describes the development of this apparatus and its application to the study of earthquake-induced landslides and the latest landslide-triggered debris flow in Japan. Also, tests of the latest version (DPRI-7) with a transparent shear box for direct observation of the shear zone during a rapid shearing are described.  相似文献   

Location and parameters of a microwave millisecond spike event   总被引：1，自引：0，他引：1  

Guangli?HuangEmail author  Hiroshi?Nakajima 《Astrophysics and Space Science》2005,295(4):423-442

A typical microwave millisecond spike event on November 2, 1997 was observed by the radio spectrograph of National Astronomical Observatories (NAOs) at 2.6–3.8 GHz with high time and frequency resolution. This event was also recorded by Nobeyama Radio Polarimeters (NoRP) at 1–35 GHz and Radio Heliograph (NoRH) at 17 GHz. The source at 17 GHz is located in one foot-point of a small bright coronal loop of YOHKOH SXT and SOHO EIT images with strong photospheric magnetic field in SOHO MDI magnetograph. It is assumed that the electron cyclotron maser instability and gyro-resonance absorption dominate, respectively, the rising and decay phase of the spike event. For different harmonic number of gyro-frequency or magnetic field strength, a fitting program with free plasma parameters is used to minimize the difference between the observational and theoretical values of the exponential growth and decay rates for a given spike. The plasma parameters at third harmonic number are more comparable to their typical values in solar corona. Hence, it is able to provide a diagnosis for the source parameters (magnetic field, density, and temperature), the properties of radiations (wave vector and propagation angle), and the properties of non-thermal electrons (density, pitch angle, and energy). The results are also comparable with the diagnosis of the gyro-synchrotron radiation model, the frequency drift rates and a dipole magnetic field model, as well as the YOHKOH SXT and SOHO MDI data. This study is supported by the NFSC project nos. 10333030 and 10273025, and “973” program with no. G2000078403.  相似文献