Weathering mechanisms and their effects on landsliding in pelitic schist     

Shintaro Yamasaki  Masahiro Chigira 《地球表面变化过程与地形》2011,36(4):481-494

Physical, chemical, and mineralogical analyses of undisturbed drill cores of pelitic schist from a landslide area in Japan clarified the mechanisms of chemical weathering of pelitic schist. Oxidizing surface water percolates downward and reaches an oxidation front, where chlorite is altered to Al‐vermiculite, graphite and pyrite are oxidized and depleted, and goethite precipitates. Oxidation of pyrite also occurs just below the oxidation front, probably by ferric iron. Pyrite oxidation yields sulphuric acid, which penetrates further downward, interacting with and weakening the rocks. In addition to this chemical weakening, stress release and shearing along schistosities form an incipient shear zone, which propagates to a sliding zone that forms the rupture surface of a landslide. Once a sliding zone has developed, it inhibits downward groundwater flow across it because of its low permeability, slowing the downward propagation of the weathering zone until this filtration barrier is broken by landslide movement. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Investigation of the sliding behavior between steel and mortar for seismic applications in structures     

Jason McCormick  Takuya Nagae  Masahiro Ikenaga  Peng‐Cheng Zhang  Mika Katsuo  Masayoshi Nakashima 《地震工程与结构动力学》2009,38(12):1401-1419

The friction developed between a steel base plate and a mortar base contributes shear resistance to the building system during a seismic event. In order to investigate the possible sliding behavior between the base plate and the mortar, a shake table study is undertaken using a large rigid mass supported by steel contact elements which rest on mortar surfaces connected to the shake table. Horizontal input accelerations are considered at various magnitudes and frequencies. The results provide a constant friction coefficient during sliding with an average value of approximately 0.78. A theoretical formulation of the friction behavior is also undertaken. The theoretical equations show that the sliding behavior is dependent on the ratio of the friction force to the input force. The addition of vertical accelerations to the system further complicates the sliding behavior as a result of the varying normal force. This results in a variable friction resistance which is a function of the amplitude, phase, and frequency of the horizontal and vertical input motions. In general, this study showed a consistent and reliable sliding behavior between steel and mortar. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

SHRIMP zircon and EPMA monazite dating of granitic rocks from the Maizuru terrane, southwest Japan: Correlation with East Asian Paleozoic terranes and geological implications   总被引：1，自引：0，他引：1  

Masahiro  Fujii  Yasutaka  Hayasaka  Kentaro  Terada 《Island Arc》2008,17(3):322-341

Abstract The Maizuru terrane, distributed in the Inner Zone of southwest Japan, is divided into three subzones (Northern, Central and Southern), each with distinct lithological associations. In clear contrast with the Southern zone consisting of the Yakuno ophiolite, the Northern zone is subdivided into the western and eastern bodies by a high-angle fault, recognized mainly by the presence of deformed granitic rocks and pelitic gneiss. This association suggests an affinity with a mature continental block; this is supported by the mode of occurrence, and petrological and isotopic data. Newly obtained sensitive high mass-resolution ion microprobe (SHRIMP) zircon U–Pb ages reveal the intrusion ages of 424 ± 16 and 405 ± 18 Ma (Siluro–Devonian) for the granites from the western body, and 249 ± 10 and 243 ± 19 Ma (Permo–Triassic) for the granodiorites from the eastern body. The granites in the western body also show inherited zircon ages of around 580 and 765 Ma. In addition, electron probe microanalysis (EPMA) monazite U–Th–total Pb dating gives around 475–460 Ma. The age of intrusion, inherited ages, mode of occurrence, and geological setting of the Siluro–Devonian granites of the Northern zone all show similarities with those of the Khanka Massif, southern Primoye, Russia, and the Hikami granitic rocks of the South Kitakami terrane, Northeast Japan. We propose that both the Siluro–Devonian and Permo–Triassic granitic rocks of the Northern zone are likely to have been juxtaposed through the Triassic–Late Jurassic dextral strike-slip movement, and to have originated from the Khanka Massif and the Hida terrane, respectively. This study strongly supports the importance of the strike-slip movement as a mechanism causing the structural rearrangement of the Paleozoic–Mesozoic terranes in the Japanese Islands, as well as in East Asia.  相似文献   

Evaluation of ionic pollutants in cloud droplets at a mountain ridge in northern Japan using constrained oblique rotational factor analysis     

Nobuaki Ogawa  Ryoei Kikuchi  Tomoko Okamura  Junko Inotsume  Tetsuya Adzuhata  Toru Ozeki  Masahiro Kajikawa 《Atmospheric Research》2000,54(4)

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Collapse and fragmentation of rotating magnetized clouds – I. Magnetic flux–spin relation     

Masahiro N. Machida  Tomoaki Matsumoto  Kohji Tomisaka  Tomoyuki Hanawa 《Monthly notices of the Royal Astronomical Society》2005,362(2):369-381

We discuss the evolution of the magnetic flux density and angular velocity in a molecular cloud core, on the basis of three-dimensional numerical simulations, in which a rotating magnetized cloud fragments and collapses to form a very dense optically thick core of  >5 × 10¹⁰ cm⁻³  . As the density increases towards the formation of the optically thick core, the magnetic flux density and angular velocity converge towards a single relationship between the two quantities. If the core is magnetically dominated its magnetic flux density approaches  1.5( n /5 × 10¹⁰ cm⁻³)^1/2 mG  , while if the core is rotationally dominated the angular velocity approaches  2.57 × 10⁻³ ( n /5 × 10¹⁰ cm⁻³)^1/2 yr⁻¹  , where n is the density of the gas. We also find that the ratio of the angular velocity to the magnetic flux density remains nearly constant until the density exceeds  5 × 10¹⁰ cm⁻³  . Fragmentation of the very dense core and emergence of outflows from fragments will be shown in the subsequent paper.  相似文献   

Control of Phosphate Concentration through Adsorption and Desorption Processes in Groundwater and Seawater Mixing at Sandy Beaches in Tokyo Bay, Japan     

Masahiro Suzumura  Shingo Ueda  Eiichi Sumi 《Journal of Oceanography》2000,56(6):667-673

Field observation was conducted to monitor phosphate concentrations in groundwater and seawater mixing at two sandy beaches in Futtsu and Miura in Tokyo Bay, Japan. Dissolved phosphate concentrations were measured along transects from fresh groundwater aquifer to seawater adjacent the beaches. The concentrations were often high (up to 46 µM) in fresh groundwater samples (Cl^– < 0.2). Coastal seawater, on the other hand, exhibited low phosphate concentrations (1.5 µM or less). Along the transects, phosphate generally displayed non-conservative behavior during mixing of fresh and saline waters in the aquifer; concentrations as high as 100 µM were found around the upper limit of seawater intrusion (Cl^– = 2). Laboratory experiments were executed to identify the processes that control the phosphate behavior in the mixing processes. The results revealed that adsorption-desorption processes by the aquifer sand particles could significantly control the phosphate concentrations in the groundwater. Furthermore, the adsorption and/or desorption was found to be a function of salinity; the equilibrium concentration of dissolved phosphate in slurry of sand and water was the highest in freshwater and decreased considerably in saline water. The extreme concentration of phosphate may be caused by release from sand particles coinciding with the rapid change in salinity with tide.  相似文献   

Formation of thermohaline front by cooling of the sea surface and inflow of the fresh water     

Masahiro Endoh 《Journal of Oceanography》1977,33(1):6-15

A numerical study of characteristics of the front formed by cooling of the sea surface and inflow of the fresh water is made within a vertical two-dimensional plane without the rotation of the earth. The convective adjustment technique is employed to parameterize the small scale convective overturning process.A sharply edged shelf causing the marked difference of the heat capacity of the water columns between over the shelf (50 m depth) and in the deeper region (150 m depth), is responsible for the formation of a thermal front over the shelf edge and two cell circulations of the same sense with each other adjoining at the frontal region.Inflow of the fresh water at the upper region of the coast (which is equivalently replaced by the outflow of the salt from the same region) adds a circulation of the opposite sense to the above ones, which transports the water of low salinity and low temperature offshore and forms a sharp front both of temperature and salinity with the offshore water of high salinity and high temperature. This thermohaline front or Oceanic front has a remarkable character that the horizontal density gradient is minimal at the front due to the counteracting contributions of temperature and salinity to density. Response of this front to the sudden ceases of the surface cooling and the fresh water supply, is also studied in order to understand its transient behaviors.  相似文献   

A numerical investigation of western boundary currents in subtropical and subpolar gyres with a barotropic model     

Masahiro Endoh 《Journal of Oceanography》1973,29(4):148-154

Dynamics of western boundary currents in the subtropical and subpolar gyres are studied as a source-sink flow of barotropic fluid by means of numerical integration of the time-dependent non-linear vorticity equation. The bottom topography consists of a continental shelf of uniform slope (120 km wide) parallel to the straight western coast and a flat bottom of uniform depth. The steady solution in the case of low Reynolds number (Re≦100) shows the vorticity balance of the western boundary current between theβ-, diffusion-, and bottom relief terms. The cuspidated flow of the western boundary current in the subpolar gyre is observed as a compensating flow for the subtropical western boundary current separating from the western coast. In the case of Re=350, the zonal current separating from the coast meanders with the wave length of the stationary Rossby waves. It is shown that in the present model the separation of the boundary current is controlled by the planetary vorticity (f) of the fluid particle in the boundary flow, with which the same particle flows out the eastern wall at the corresponding latitude. The decrease of the efflux width increases the intensity of the non-linear overshooting of the boundary current separating from the western coast.  相似文献   

The study of ocean circulation dynamics with numerical models     

Masahiro Endoh 《Journal of Oceanography》1980,36(2):134-140

Summarized is the author's study of the ocean circulation dynamics with numerical models, for which he was honored by the Okada Prize (1979). Cited topics are formation of the western boundary current and its variation associated with imposed wind stress, some effects of a marine ridge on the boundary current, coastal upwelling circulation and coastal thermohaline front formation. Recent modelling efforts in Japan, specifically on numerical study of ocean circulation dynamics are also reviewed.  相似文献   

Diagenetic behavior of manganese in Tokyo Bay sediment     

Masahiro Sakata  Yasushi Kitano  Eiji Matsumoto 《Journal of Oceanography》1981,37(4):212-217

To understand the behavior of manganese in diagenetic processes in sediments of an enclosed bay which is similar to those of an estuary, chemical analyses have been carried out on both sediment and interstitial water of a core sample collected from Tokyo Bay. The results suggest that redistribution of manganese takes place within the sediment as a result of the dissolution of buried manganese oxides and hydroxides under reducing condition, the downward diffusion of Mn²⁺ through the interstitial water toward lower layers and then the precipitation of carbonate. The carbonate formed in the sediment contains managanese carbonate probably as a solid solution between calcitic calcium carbonate and manganese carbonate.  相似文献