Technical Note     

K. Shin  S. Okubo 《Rock Mechanics and Rock Engineering》1999,32(3):231-236

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A note on small organism diffusion around an attractive center: A mathematical model     

Akira Okubo 《Journal of Oceanography》1972,28(1):1-7

A mathematical model of small organism diffusion around an attractive center is presented. The diffusion equation includes a forcing term which creates a virtual flow of organisms toward the center. Owing to the attractive force, the organisms tend to collect in swarms or patches notwithstanding the diffusive motion of surrounding water.Contribution No. 176 of the Chesapeake Bay Institute, Department of Earth and Planetary Sciences, The Johns Hopkins University. This work was supported by the Office of Naval Research Contract N00014-67-A-0163-0006, Research Project NR083-016, by the U.S. Atomic Energy Commission under Contract AT (30-1) 3109, Document COO-3109-2, and by National Science Foundation Grant, GA-16603.  相似文献   

Lagrangian diffusion equation and its application to oceanic dispersion     

Akira Okubo  Curtis C. Ebbesmeyer  Brian G. Sanderson 《Journal of Oceanography》1983,39(5):259-266

The Lagrangian diffusion equation appropriate for the dispersion of current followers (e. g., floats, drogues, drifters) is proposed. The analytical solution to the equation is obtained for a uniform deformation field, characterized by Lagrangian deformations and anisotropic eddy diffusivities both varying with time. Expressions are derived for the patch area and its elongation and rotation. For small values of elapsed time after the initial release the patch area can be accounted for by the exponential of the cumulative value of the horizontal divergence; the relative rate of change of the patch area can be accounted for by the horizontal divergence.  相似文献   

Static Spheroidal Deformation of Degree 1 - Consistency Relation, Stress Solution and Partials     

Shuhei Okubo  Takeshi Endo 《Geophysical Journal International》1986,86(1):91-102

This paper treats the static spheroidal deformation of degree 1 in detail. We give a physical interpretation of the consistency relation imposed on it. the relation serves as a guiding principle to find out all of its members. Following Okubo & Saito, we derive the partial derivatives of the degree 1 Love numbers with respect to density, bulk modulus and rigidity.  相似文献   

Uniaxial compression and tension tests of anthracite and loading rate dependence of peak strength   总被引：2，自引：0，他引：2  

S. Okubo  K. Fukui  Qi Qingxin 《International Journal of Coal Geology》2006,68(3-4):196-204

The mechanical characteristics of coal under uniaxial compressive stress and uniaxial tensile stress are key factors in investigations of the stability of galleries and coal faces, and are vital considerations for the efficient design of coalmines, disaster prevention, and environmental preservation. These mechanical characteristics have long been a topic of research, but remain insufficiently understood. In this study we performed uniaxial compression tests and uniaxial tension tests on coal, with particular attention to two concerns. The first was to measure the loading rate dependence of the peak strength of coal. Coal shows high sample-to-sample scatter in strength; test methods that are successful in comparatively homogeneous rock types cannot be used for coal. We therefore used an alternative test method that was recently developed by the authors. Anthracite samples were subjected to alternating slow and fast strain rates. Measured variations in stress during this process were used to estimate the loading rate dependence of peak strength. The second objective was to obtain complete stress–strain curves for coal under uniaxial tensile stress. It is difficult to hold samples secure during a tensile test; consequently, such curves have yet to be obtained. This study presents a successful application of the authors' method to the analysis of coal samples, yielding a complete stress–strain curve under tensile stress. The two methods presented here hold promise for application not only to anthracite but also to a wide variety of coals. It is possible to derive the values of the constants used in constitutive equations from the obtained experimental results. Once these equations are determined, they can be incorporated into finite-element software to investigate various time-dependent behaviors of coal and aid in the efficient design of coalmines and the prevention of subsidence and mine disasters.  相似文献   

Variability in Early Amazonian Tharsis stress state based on wrinkle ridges and strike-slip faulting     

Chris H. Okubo  Richard A. Schultz   《Journal of Structural Geology》2006,28(12):2169

We present evidence for a decrease in the magnitude of Tharsis-circumferential compressive stress during the Late Hesperian to the Middle Amazonian based on chronologic changes in the predominant style of faulting in southern Amazonis Planitia. Using high-resolution MOLA topography, we identify a population of strike-slip faults that exhibit Middle Amazonian-aged displacements of regional chrono-stratigraphic units. These strike-slip faults are adjacent to an older population of previously documented Late Hesperian-aged thrust faults (wrinkle ridges). Along-strike orientations of these thrust and strike-slip faults reveal the Tharsis-radial stress to be the area's most compressive remote principal stress and that this stress orientation and magnitude persisted throughout the Late Hesperian to the Middle Amazonian. We show that the change in the predominant style of faulting from thrust faulting to strike-slip faulting during this time requires a decrease of the Tharsis-circumferential compressive stress to a magnitude less than lithostatic load, with negligible change in stress orientation.  相似文献   

Displacement-length scaling relations for faults on the terrestrial planets     

Richard A. Schultz  Chris H. Okubo  Scott J. Wilkins   《Journal of Structural Geology》2006,28(12):2182

Displacement-length (D/L)scaling relations for normal and thrust faults from Mars, and thrust faults from Mercury, for which sufficiently accurate measurements are available, are consistently smaller than terrestrial D/L ratios by a factor of about 5, regardless of fault type (i.e. normal or thrust). We demonstrate that D/L ratios for faults scale, to first order, with planetary gravity. In particular, confining pressure modulates: (1) the magnitude of shear driving stress on the fault; (2) the shear yield strength of near-tip rock; and (3) the Young's (or shear) modulus of crustal rock. In general, all three factors decrease with gravity for the same rock type and pore-pressure state (e.g. wet conditions). Faults on planets with lower surface gravities, such as Mars and Mercury, demonstrate systematically smaller D/L ratios than faults on larger planets, such as Earth. Smaller D/L ratios of faults on Venus and the Moon are predicted by this approach, and we infer still smaller values of D/L ratio for faults on icy satellites in the outer solar system. Collection of additional displacement-length and down-dip height data from terrestrial normal, strike-slip, and thrust faults, located within fold-and-thrust belts, plate margins, and continental interiors, is required to evaluate the influence of fault shape and progressive deformation on the scaling relations for faults from Earth and elsewhere.  相似文献   

Estimating Crustal Heterogeneity from Double-difference Tomography     

Jean -Luc Got  Vadim Monteiller  Jean Virieux  Paul Okubo 《Pure and Applied Geophysics》2006,163(2-3):405-430

Seismic velocity parameters in limited, but heterogeneous volumes can be inferred using a double-difference tomographic algorithm, but to obtain meaningful results accuracy must be maintained at every step of the computation. MONTEILLER et al. (2005) have devised a double-difference tomographic algorithm that takes full advantage of the accuracy of cross-spectral time-delays of large correlated event sets. This algorithm performs an accurate computation of theoretical travel-time delays in heterogeneous media and applies a suitable inversion scheme based on optimization theory. When applied to Kilauea Volcano, in Hawaii, the double-difference tomography approach shows significant and coherent changes to the velocity model in the well-resolved volumes beneath the Kilauea caldera and the upper east rift. In this paper, we first compare the results obtained using MONTEILLER et al.'s algorithm with those obtained using the classic travel-time tomographic approach. Then, we evaluated the effect of using data series of different accuracies, such as handpicked arrival-time differences (``picking differences'), on the results produced by double-difference tomographic algorithms. We show that picking differences have a non-Gaussian probability density function (pdf). Using a hyperbolic secant pdf instead of a Gaussian pdf allows improvement of the double-difference tomographic result when using picking difference data. We completed our study by investigating the use of spatially discontinuous time-delay data.  相似文献   

Electromagnetic Radiation from Rock During Uniaxial Compression Testing: The Effects of Rock Characteristics and Test Conditions   总被引：3，自引：0，他引：3  

K. Fukui  S. Okubo  T. Terashima 《Rock Mechanics and Rock Engineering》2005,38(5):411-423

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Curie-point depth from spectral analysis of magnetic data in central-southern Europe   总被引：3，自引：0，他引：3  

P. Chiozzi  Y. Okubo  M. Verdoya 《Physics of the Earth and Planetary Interiors》2005,152(4):267-276

The basal depth of the outer layer with internal magnetic sources was calculated from magnetic data available within a roughly 500 km wide and 1200 km long area, running from central Germany to southern Italy. The dataset, deriving from different aeromagnetic surveys, is reduced to the reference altitude of 3000 m a.s.l. and a reference year of 1980.0. The adopted method, which transforms the spatial data into the frequency domain, provides a relationship between the two-dimensional spectrum of the magnetic anomalies and the top and centroid depths of the magnetic sources. The magnetic layer bottom depth (MLBD) thus obtained is 29-33 km deep in the stable areas (central Europe Variscan units, Corsica-Sardinia Variscan block) and corresponds to the Moho, having an average temperature of 560 °C. From the Alps to the Apennines, MLBD ranges between 22 and 28 km and is clearly shallower than the Moho. In these units, the wide variation of MLBD appears to be compatible with the presence of shallow magnetised bodies, consisting of lower crustal rocks (Ivrea-Verbano zone), ophiolitic units (Penninic zone and Voltri Massif) and intrasedimentary basic volcanic bodies (Po Basin). An average value of 25 km can be attributed to MLBD, which corresponds to a temperature of 550 °C. In the peri-Tyrrhenian zone and the Ligurian Sea, MLBD is below the Moho, which ranges from 17 to 20 km depth, and it has a temperature matching approximately to the Curie temperature of magnetite (580 °C).  相似文献