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101.
Tadahiko Tsuruta Hisaya Harada Toshiharu Misonou Toshiyuki Matsuoka Yasuyuki Hodotsuka 《Journal of Oceanography》2017,73(5):547-558
Investigations including a bathymetric survey, sonic prospecting, and vibrocoring were performed to understand the horizontal and vertical distribution of 137Cs in seabed sediments in shallow seas with depths less than 30 m near the Fukushima Daiichi Nuclear Power Plant. Especially, features of 137Cs distributions in deeper sections of the seabed sediments were studied to evaluate the vertical heterogeneity of 137Cs distribution in the seabed sediments in shallow seas. The distribution area of the seabed sediments was less than half of the investigation area, and the locations of the seabed sediments were divided into flat and terrace-like seafloors based on their topographical features. The thicknesses of the seabed sediment layers were mostly <2 m. The 137Cs inventories in the seabed sediments varied from 13 ± 1 to 3,510 ± 26 kBq m?2, and continuous distributions of 137Cs at depths greater than 81 cm were observed. The 137Cs distributions were not uniform; however, the 137Cs inventories tended to be larger near the base of the steeper ascending slopes than in the terrace-like seafloors themselves. Based on the relationship between the 137Cs inventories and mean shear stress, features of the seafloor topography were inferred to be significant control factors governing the horizontal and vertical distribution of 137Cs in the seabed sediments. Rapid changes and multiple peaks in the vertical profile of the 137Cs distributions suggest that they are related to pulse input caused by heavy-rain events. Change in the 137Cs inventories with depth in this study are larger than those reported in previous studies, indicating earlier results of 137Cs inventories per unit in seabed sediments in shallow seas, especially near the river mouth, which drains a radiologically highly-contaminated basin, were underestimated. 相似文献
102.
Influence of microbial photosynthesis on tufa stromatolite formation and ambient water chemistry, SW Japan 总被引:1,自引:0,他引:1
Photosynthetic influences on tufa stromatolite formation and ambient water chemistry were investigated at two well-studied streams depositing tufa in Southwestern Japan (Shirokawa and Shimokuraida). The tufa stromatolites in both streams are composed of fine-grained calcite crystals showing annual lamination, and colonized by a number of filamentous cyanobacteria as well as non-phototrophic bacteria. Microelectrode measurements of pH, O2, and Ca2+ near the stromatolite surface (the diffusive boundary layer; DBL) revealed that the investigated tufa stromatolites are formed by photosynthesis-induced CaCO3 precipitation (PCP): cyanobacterial photosynthesis induces calcite precipitation under light conditions, while respiration of cyanobacteria and non-phototrophic bacteria inhibits precipitation in the dark. The bulk water chemistry at the lower sites of the investigated streams showed the daytime decreases of Ca2+ concentration and alkalinity that was expected for significant influence of PCP, while the other expected change, increased pH, was not observed. In order to examine this discrepancy, a novel approach using semi-in situ microelectrode measurements was applied to perform precise quantitative calculations. The calculation results demonstrated that the observed Ca2+ concentration and alkalinity decreases were caused by PCP, and that the concomitant pH increase was expected to be under the detection level of a conventional pH meter. Although the amount of PCP is supposed to be significantly affected by light intensity, observations in Shimokuraida revealed that the amount of PCP on cloudy day nonetheless accounted for about 80% of that on sunny day. Despite the significant role of PCP for tufa stromatolite formation, PCP accounted for only about 10% of the precipitated calcite in the investigated streams, which indicates that tufa stromatolites, the characteristic deposits in the streams, are responsible for only a small portion of calcite precipitation, and the rest is considered to precipitate inorganically at biofilm-free substrates. 相似文献
103.
The α − β transition of quartz was successfully observed with using a single sample by means of the rectangular parallelepiped
resonance (RPR) method. An oriented rectangular parallelepiped of α-quartz single crystal was prepared and the resonant frequencies
of 30–11 vibrational modes were measured from room temperature to 700°C. The softening of quartz crystal was observed as the
significant reduction of resonant frequencies near the α–β transition. The present study is the first application of the RPR
method to the study of phase transition. The complete set of elastic constants of α- and β-quartz were determined as a function
of temperature by the least-squares inversion of the measured frequency data obtained by a single run. This is a merit yielded
by the RPR method. It is shown near the α − β transition in both α- and β-quartz that the elastic parameters decrease proportionally
to |T−T
0|−n
, where T is temperature and T
0 is the transition temperature, 573.0°C for α-quartz and 574.3°C for β-quartz. It was also seen that linear incompressibilities
K
1 = (C
11
+C
12
+C
13)/3 and K
3 = (C
33
+2C
13)/3 decrease rapidly toward the transition, whereas, shear moduli C
44, C
S1 = (C
11
+C
33
-2C
13)/4 and C
S3 = (C
11
-C
12)/2 = C
66 decrease only slightly. The shear modulus C
S3 = C
66 increased slightly in α-quartz. The elastic properties of isotropic aggregate of quartz were calculated, and it is shown
that the longitudinal wave velocity significantly decreases at the α − β transition, whereas, the shear wave velocity decreases
only slightly. 相似文献
104.
M. Nakagawa M. Santosh S. Yoshikura M. Miura T. Fukuda A. Harada 《Gondwana Research》2006,9(4):530-538
The kaolin deposits at Melthonnakkal and Pallipuram mines form part of the Warkalli Formation belonging to the Tertiary sequence in southern Kerala and occur at the boundary between the Tertiary sequence and Precambrian granulite facies metapelites (khondalites). The sedimentary clays are composed mainly of kaolinite, quartz and gibbsite. XRD and SEM studies have revealed that kaolinite is well-crystallized variety and the platy crystals are scarcely broken in the sedimentary clays. These sedimentary kaolins are considered to have been formed by intense tropical weathering of the khondalites, and subsequently transported and deposited with high organic input into lakes near the weathering crust over the basement rock. Besides, the surficial parts of the sedimentary deposits are extensively lateritized with the formation of goethite and hematite by Quaternary tropical weathering processes. 相似文献
105.
Motomu Toda Masayuki Yokozawa Akihiro Sumida Tsutomu Watanabe Toshihiko Hara 《Carbon balance and management》2007,2(1):1-18
This editorial provides a subject index from published articles, active researchers, and published papers in the field of
carbon balance and management. 相似文献
106.
Norimasa Nishiyama Takehiko Yagi Shigeaki Ono Hirotada Gotou Tatsuhiko Harada Takumi Kikegawa 《Physics and Chemistry of Minerals》2007,34(3):131-143
In situ X-ray diffraction measurements of Fe- and Al-bearing MgSiO3-rich perovskite (FeAl-Pv), which was synthesized from a natural orthopyroxene, were performed at pressures of 19–32 GPa and
temperatures of 300–1,500 K using a combination of a Kawai-type apparatus with eight sintered-diamond anvils and synchrotron
radiation. Two runs were performed using a high-pressure cell with two sample chambers, and both MgSiO3 perovskite (Mg-Pv) and FeAl-Pv were synthesized simultaneously in the same cell. Thus we were able to measure specific volumes
(V/V
0) of Mg-Pv and FeAl-Pv at the same P−T conditions. At all the measurement conditions, values of the specific volume of FeAl-Pv are consistent with those of Mg-Pv
within 2 Standard Deviation, strongly suggesting that effect of incorporation of iron and aluminum on the thermoelastic properties
of magnesium silicate perovskite is undetectable in this composition, pressure, and temperature range. Two additional runs
were performed using a high-pressure cell that has one sample chamber and unit-cell volumes of FeAl-Pv were measured at pressures
and temperatures up to 32 GPa and 1,500 K, respectively. All the unit-cell volume data of FeAl-Pv perovskite were fitted to
the high temperature Birch–Murnaghan equation of state and a complete set of thermoelastic parameters of this perovskite was
determined with an assumption of K′
300,0 = 4. The determined parameters are K
300,0 = 243(3) GPa, (∂K
T,0/∂T)
P
= −0.030(8) GPa/K, a
0 = 2.78(18) × 10−5 K−1, and b
0 = 0.88(28) × 10−8 K−2, where a
0 and b
0 are the coefficients of the following expression describing the zero-pressure thermal expansion: α
T,0 = a
0 + b
0
T. The equation-of-state parameters of FeAl-Pv are in good agreement with those of MgSiO3 perovskite at the conditions corresponding to the uppermost part of the lower mantle. 相似文献
107.
Electric currents along earthquake faults and the magnetization of pseudotachylite veins 总被引:2,自引:1,他引:2
Friedemann Freund Manuel A. Salgueiro da Silva Bobby W.S. Lau Akihiro Takeuchi Hollis H. Jones 《Tectonophysics》2007,431(1-4):131
Pseudotachylites occur in the form of thin glassy veins quenched from frictional melts along the fault planes of major earthquakes. They contain finely grained magnetite and often exhibit a high natural remanent magnetization (NRM). High NRM values imply strong local electric currents. These currents must persist for some time, while the pseudotachylite veins cool through the Curie temperature of magnetite around 580 °C. There is no generally accepted theory explaining how such powerful, persistent currents may be generated along the fault plane. Data presented here suggest the activation of electronic charge carriers, which are present in igneous rocks in a dormant, inactive form. These charge carriers can be “awakened” by the application of stress. They are electrons and defect electrons, also known as positive holes or p-holes for short. While p-holes are capable of spreading out of the stressed rock volume into adjacent p-type conductive unstressed rocks, electrons require a connection to the hot, n-type conductive lower crust. However, as long as the (downward) electron flow is not connected, the circuit is not closed. Hence, with the outflow of p-holes impeded, no current can be sustained. This situation is comparable to that of a charged battery where one pole remains unconnected. The friction melt that forms coseismically during rupture, provides a conductive path downward, which closes the circuit. This allows a current to flow along the fault plane. Extrapolating from laboratory data, every km3 of stressed igneous rocks adjacent to the fault plane can deliver 103–105 A. Hence, the current along the fault plane will not be limited by the number of charge carriers but more likely by the (electronic) conductivity of the cooling pseudotachylite vein. The sheet current will produce a magnetic field, whose vectors will lie in the fault plane and perpendicular to the flow direction. 相似文献
108.
109.
Comparative study of cataclastic rocks from a drill core and outcrops of the Nojima Fault zone on Awaji Island, Japan 总被引:3,自引:0,他引:3
110.
Hidemi Tanaka Shin-Ichiro Hinoki Kazuo Kosaka Aiming Lin Keiji Takemura Akihiro Murata Takao Miyata 《Island Arc》2001,10(3-4):381-391
Abstract This paper describes the results of petrographical and meso- to microstructural observations of brittle fault rocks in cores obtained by drilling through the Nojima Fault at a drilling depth of 389.52 m. The zonation of deformation and alteration in the central zone of the fault is clearly seen in cores of granite from the hanging wall, in the following order: (i) host rock, which is characterized by some intragranular microcracks and in situ alteration of mafic minerals and feldspars; (ii) weakly deformed and altered rocks, which are characterized by transgranular cracks and the dissolution of mafic minerals, and by the precipitation of zeolites and iron hydroxide materials; (iii) random fabric fault breccia, which is characterized by fragmentation, by anastomosing networks of transgranular cracks, and by the precipitation of zeolites and iron hydroxide materials; and (iv) fault gouge, which is characterized by the precipitation of smectite and localized cataclastic flow. This zonation implies that the fault has been weakened gradually by fluid-related fracturing over time. In the footwall, a gouge layer measuring only 15 mm thick is present just below the surface of the Nojima Fault. These observations are the basis for a model of fluid behavior along the Nojima Fault. The model invokes the percolation of meteoric fluids through cracks in the hanging wall fault zone during interseismic periods, resulting in chemical reactions in the fault gouge layer to form smectite. The low permeability clay-rich gouge layer sealed the footwall. The fault gouge was brecciated during coseismic or postseismic periods, breaking the seal and allowing fluids to readily flow into the footwall, thus causing a slight alteration. Chemical reactions between fluids and the fault breccia and gouge generated new fault gouge, which resealed the footwall, resulting in a low fluid condition in the footwall during interseismic periods. 相似文献