Cohesive Crack Analysis of Toughness Increase Due to Confining Pressure     

Kazushi Sato  Toshiyuki Hashida 《Pure and Applied Geophysics》2006,163(5-6):1059-1072

Apparent fracture toughness in Mode I of microcracking materials such as rocks under confining pressure is analyzed based on a cohesive crack model. In rocks, the apparent fracture toughness for crack propagation varies with the confining pressure. This study provides analytical solutions for the apparent fracture toughness using a cohesive crack model, which is a model for the fracture process zone. The problem analyzed in this study is a fluid-driven fracture of a two-dimensional crack with a cohesive zone under confining pressure. The size of the cohesive zone is assumed to be negligibly small in comparison to the crack length. The analyses are performed for two types of cohesive stress distribution, namely the constant cohesive stress (Dugdale model) and the linearly decreasing cohesive stress. Furthermore, the problem for a more general cohesive stress distribution is analyzed based on the fracture energy concept. The analytical solutions are confirmed by comparing them with the results of numerical computations performed using the body force method. The analytical solution suggests a substantial increase in the apparent fracture toughness due to increased confining pressures, even if the size of the fracture process zone is small.  相似文献   

Groundwater-level Changes Due to Pressure Gradient Induced by Nearby Earthquakes off Izu Peninsula, 1997     

Masao Ohno  Tsutomu Sato  Kenji Notsu  Hiroshi Wakita  Kunio Ozawa 《Pure and Applied Geophysics》2006,163(4):647-655

Anomalous water level changes were observed at two wells associated with seismic swarm activity off Izu Peninsula on March, 1997. These are coseismic water level drops followed by gradual postseismic water level rise at the time of large earthquakes during the swarm activity. The post-seismic water level rises, which can be fitted by an exponential function with a time constant of about six hours, are explained in terms of the horizontal pressure diffusion due to the pressure gradient in the aquifer induced by the coseismic static strain.  相似文献   

Diffuse Emission of CO2 from Showa-Shinzan, Hokkaido, Japan: A Sign of Volcanic Dome Degassing   总被引：1，自引：0，他引：1  

Pedro A. Hernández  Kenji Notsu  Hiromu Okada  Toshiya Mori  Masanori Sato  Francisco Barahona  Nemesio M. Pérez 《Pure and Applied Geophysics》2006,163(4):869-881

Two soil CO₂ efflux surveys were carried out in September 1999 and June 2002 to study the spatial distribution of diffuse CO₂ degassing and estimate the total CO₂ output from Showa-Shinzan volcanic dome, Japan. Seventy-six and 81 measurements of CO₂ efflux were performed in 1999 and 2002, respectively, covering most of Showa-Shinzan volcano. Soil CO₂ efflux data showed a wide range of values up to 552 g m^-2 d^-1. Carbon isotope signatures of the soil CO₂ ranged from -0.9‰ to -30.9‰, suggesting a mixing between different carbon reservoirs. Most of the study area showed CO₂ efflux background values during the 1999 and 2002 surveys (B = 8.2 and 4.4 g m^-2 d^-1, respectively). The spatial distribution of CO₂ efflux anomalies for both surveys showed a good correlation with the soil temperature, indicating a similar origin for the extensive soil degassing generated by condensation processes and fluids discharged by the fumarolic system of Showa-Shinzan. The total diffuse CO₂ output of Showa-Shinzan was estimated to be about 14.0–15.6 t d^-1 of CO₂ for an area of 0.53 km².  相似文献   

Effect of hydrostatic pressure on the lattice parameters of Fe₂SiO₄ olivine up to 70 kbar     

Takehiko Yagi  Yoshiaki Ida  Yosiko Sato  Syun-Iti Akimoto 《Physics of the Earth and Planetary Interiors》1975,10(4):348-354

The pressure dependence of the three lattice parameters and unit cell volume of fayalite (Fe₂SiO₄ olivine) was determined by X-ray diffraction under hydrostatic pressures up to 70 kbar. In order to eliminate stress inhomogeneity within a composite material consisting of a specimen mixed with an internal-pressure standard, a liquid (1 : 1 mixture of ethanol and methanol) was used as a pressure-transmitting medium. The isothermal bulk modulus calculated on the basis of the second-order Birch-Murnaghan equation of state gives the values K₀ = 1.19 ± 0.10 Mbar and K₀′ = 7 ± 4, and if we assume K₀′ = 5: K₀ = 1.24 ± 0.02 Mbar. Three axes of fayalite were found to be compressible in the following order, b >c >a. Comparisons with the results obtained under non-hydrostatic compression are made.  相似文献   

Fast Oxidation Reaction of Nitrite by Dissolved Oxygen in the Freezing Process in the Tropospheric Aqueous Phase     

Norimichi Takenaka  Tohru Daimon  Akihiro Ueda  Keiichi Sato  Masaru Kitano  Hiroshi Bandow  Yasuaki Maeda 《Journal of Atmospheric Chemistry》1998,29(2):135-150

Nitrite oxidation in the tropospheric aqueous phase by freezing was evaluated by freezing a field sample. Nitrite oxidation by dissolved oxygen in the freezing process is much faster than by other oxidation processes, such as reactions with ozone, hydrogen peroxide or dissolved oxygen in an aqueous solution at pHs 3 to –6. At pH 4.5 and 25°C, the lifetime of nitrite in the aqueous phase is ca. 1 hr in oxidation by ozone (6×10^-10 mol dm^-3), ca. 10 hr in oxidation by H₂O₂ (2×10^-4 mol dm^-3), and 7.5 hr (Fischer and Warneck, 1996) in photodissociation at midday in summer. Under the same conditions at a temperature below 0°C, the lifetime of nitrite in the freezing process is estimated as ca. 2 sec when the droplets are frozen within a second. The reaction by freezing is affected by the presence of salts, such as NaCl or KCl, or orgnaic compounds, such as methanol or acetone. The results of freezing a field rain or fog sample showed that nitrite oxidation proceeds below pH 6, and the conversion ratio of nitrate from nitrite increases with decreasing pH. The oxidation of nitrite by freezing was also observed in freezing fog particles generated by an ultrasonic humidifier. The ratios of the concentrations of ions in the winter sample to those in the summer sample (or those in the fog sample) were almost the same values. However, the concentration of nitrite in the winter sample was lower than that estimated by the ratios of other ions. From the present study, it seems that the freezing process plays an important role in the nitrite sink process in the tropospheric aqueous phase.  相似文献   

Frequency-dependent Attenuation of High-frequency P and S Waves in the Upper Crust in Western Nagano, Japan     

K. Yoshimoto  H. Sato  Y. Iio  H. Ito  T. Ohminato  M Ohtake 《Pure and Applied Geophysics》1998,153(2-4):489-502

—Borehole seismograms from local earthquakes in the aftershock region of the 1984 western Nagano Prefecture, Japan earthquake were analyzed to measure the frequency-dependent characteristics of P- and S-wave attenuation in the upper crust. The records from a three-component velocity seismometer at the depth of 145m exhibit high S/N-ratio in a wide frequency range up to 100 Hz. Extended coda normalization methods were applied to bandpass-filtered seismograms of frequencies from 25 to 102 Hz. For the attenuation of high-frequency P and S waves, our measurements show Q _P ^-1? 0.052?^-0.66 and Q _S ^-1? 0.0034?^-0.12 respectively. The frequency dependence of the quality factor of S waves is very weak as compared with that of P waves. The ratio of Q _P ^-1/Q _S ^-1 is larger than unity in the entire analyzed frequency range.  相似文献   

A new technique for measuring diffusion coefficients of cations and anions in ionic crystals     

Hiroki Sato  Yoshiaki Ida 《Physics of the Earth and Planetary Interiors》1981,25(4):396-405

A new technique has been developed for measuring the diffusion coefficient in ionic crystals. Based on Einstein's formula expressing the relation between diffusion coefficient and electric mobility, the electrical impedance of a diatomic ionic crystal is derived theoretically as a function of frequency of the applied electric field. In this method, the diffusion coefficients of both cations and anions are determined simultaneously by fitting the measured impedance to the theoretical relation. This method was applied to NaCl single crystals in the temperature range 370–780°C. The impedance was determined over the frequency range 0.01 Hz to 1 kHz, at constant temperature. The diffusion coefficients thus obtained for NaCl agree reasonably well with previous data by means of a radioactive isotope technique. The activation energies for Na⁺ and Cl^? obtained are 1.97±0.03 eV and 2.08±0.06 eV, respectively, in the intrinsic region, and 0.92±0.02 eV and 1.06±0.02 eV in the extrinsic region. It was discovered that there are diffusion blocks of approximately 2 μm width, which obstruct free migration of ions in a single crystal.  相似文献   

Local effects on tidal strain measurements at Esashi, Japan     

T. Sato  J. C. Harrison 《Geophysical Journal International》1990,102(3):513-526

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Long-term evolution of the aerosol debris cloud produced by the 2009 impact on Jupiter     

A. Sánchez-Lavega  G.S. Orton  R. Hueso  L.N. Fletcher  E. García-Melendo  I. de Pater  H.B. Hammel  A. Simon-Miller  F. Marchis  O. Mousis  J. García-Rojas  M. Cecconi  K. Noll  S. Pedraz  P. Kalas  W. Golisch  P. Sears  V. Reddy  R. Binzel  W. Grundy  J. Emery  A. Rivkin  C. Thomas  D. Trilling  K. Bjorkman  A.J. Burgasser  H. Campins  T.M. Sato  Y. Kasaba  J. Ziffer  R. Mirzoyan  H. Bouy 《Icarus》2011,214(2):462-476

We present a study of the long-term evolution of the cloud of aerosols produced in the atmosphere of Jupiter by the impact of an object on 19 July 2009 (Sánchez-Lavega, A. et al. [2010]. Astrophys. J. 715, L155-L159). The work is based on images obtained during 5 months from the impact to 31 December 2009 taken in visible continuum wavelengths and from 20 July 2009 to 28 May 2010 taken in near-infrared deep hydrogen-methane absorption bands at 2.1-2.3 μm. The impact cloud expanded zonally from ∼5000 km (July 19) to 225,000 km (29 October, about 180° in longitude), remaining meridionally localized within a latitude band from 53.5°S to 61.5°S planetographic latitude. During the first two months after its formation the site showed heterogeneous structure with 500-1000 km sized embedded spots. Later the reflectivity of the debris field became more homogeneous due to clump mergers. The cloud was mainly dispersed in longitude by the dominant zonal winds and their meridional shear, during the initial stages, localized motions may have been induced by thermal perturbation caused by the impact’s energy deposition. The tracking of individual spots within the impact cloud shows that the westward jet at 56.5°S latitude increases its eastward velocity with altitude above the tropopause by 5-10 m s⁻¹. The corresponding vertical wind shear is low, about 1 m s⁻¹ per scale height in agreement with previous thermal wind estimations. We found evidence for discrete localized meridional motions with speeds of 1-2 m s⁻¹. Two numerical models are used to simulate the observed cloud dispersion. One is a pure advection of the aerosols by the winds and their shears. The other uses the EPIC code, a nonlinear calculation of the evolution of the potential vorticity field generated by a heat pulse that simulates the impact. Both models reproduce the observed global structure of the cloud and the dominant zonal dispersion of the aerosols, but not the details of the cloud morphology. The reflectivity of the impact cloud decreased exponentially with a characteristic timescale of 15 days; we can explain this behavior with a radiative transfer model of the cloud optical depth coupled to an advection model of the cloud dispersion by the wind shears. The expected sedimentation time in the stratosphere (altitude levels 5-100 mbar) for the small aerosol particles forming the cloud is 45-200 days, thus aerosols were removed vertically over the long term following their zonal dispersion. No evidence of the cloud was detected 10 months after the impact.  相似文献   

Geochemical study of arsenic and other trace elements in groundwater and sediments of the Old Brahmaputra River Plain,Bangladesh   总被引：1，自引：1，他引：0  

Faruque Ahmed  M. Hawa Bibi  Hiroaki Ishiga  Takehiko Fukushima  Teruyuki Maruoka 《Environmental Earth Sciences》2010,60(6):1303-1316

The geochemical study of groundwaters and core sediments from the Old Brahmaputra plain of Bangladesh was conducted to investigate the distribution of arsenic and related trace elements. Groundwaters from tube wells are characterized by pH of 6.4–7.4, dissolved oxygen (DO) of 0.8–1.8 mg/l, Ca contents of 5–50 mg/l, and Fe contents of 0.2–12.9 mg/l. Arsenic concentrations ranged from 8 to 251 μg/l, with an average value of 63 μg/l. A strong positive correlation exists between As and Fe (r ² = 0.802; p = 0.001) concentrations in groundwater. The stratigraphic sequences in the cores consist of yellowish silty clays at top, passing downward into grayish to yellowish clays and sands. The uppermost 3 m and lower parts (from 13 to 31 m) of the core sediments are oxidized (average oxidation reduction potential (ORP) +170 and +220 mV, respectively), and the ORP values gradually become negative from 3 to 13 m depths (−35 to −180 mV), indicating that anoxic conditions prevail in the shallow aquifers of the Brahmaputra plain. Age determinations suggest that clay horizons at ~10 m depth were deposited at around 2,000 and 5,000 years BP (¹⁴C ages) during the transgressive phase of sea-level change. Elevated concentrations of As, Pb, Zn, Cu, Ni, Cr, and V are present in the silts and clays, probably due to adsorption onto clay particles. Significant concentrations of As occur in black peat and peaty sediments at depths between 9 and 13 m. A strong positive correlation between As and Fe was found in the sediments, indicating As may be adsorbed onto Fe oxides in aquifer sediments.  相似文献