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111.
Temporal and spatial variation of infilling processes in a landslide scar in a steep mountainous region,Japan 下载免费PDF全文
The duration of the soil‐depth recovery needed for reoccurrence of shallow colluvial landslides at a given site in humid regions is much longer than the return period of rainfall needed to generate sufficient pore water pressure to initiate a landslide. Knowledge of the rate of change in soil depth in landslide scars is therefore necessary to evaluate return intervals of landslides. Spatial variation in sediment transport at the Kumanodaira landslide scar in central Japan was investigated by field observations. Spatial distribution of the rate of change in soil depth was estimated using sediment transport data and geographic information system (GIS) analysis. Observations revealed that the timing of sediment transport differed for shallow and deep soil layers. Near‐surface sediment transport (mostly dry ravel and some shallow soil creep at depths ≤0·05 m) measured in sediment traps was active in winter and early spring and was affected by freezing–thawing; soil creep of subsoil (i.e. >0·05 m), monitored by strain probes, was active in summer and autumn when precipitation was abundant. Near‐surface sediment flux was estimated by a power law function of slope gradient. Deeper soil creep was more affected by relative location to the landslide scar, which influences soil depth, than by slope gradient. Our study indicated that the rate of soil‐depth recovery is high just below the head scarp of the landslide. Abrupt changes in the longitudinal slope topography immediately above, within and just below the head scarp became smoother with time due to degradation proximate to the landslide head scarp and flanks, as well as aggradation just below the head scarp. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
112.
Endo T Hisamichi Y Haraguchi K Kato Y Ohta C Koga N 《Marine pollution bulletin》2008,56(10):1774-1780
We analyzed Hg, Zn and Cu concentrations in the liver and muscle of tiger sharks (Galeocerdo cuvier) from the coast of Ishigaki Island, Japan. The Hg concentration in the muscle increased proportionally with body length in the tiger sharks, whereas that in the liver increased rapidly after maturity (defined by a length of over 2.7 m). Muscle Hg levels were higher than liver concentrations in immature sharks, with the inverse trend observed in mature sharks. Notably, the Zn and Cu concentrations in the liver tended to decrease with increasing body length. This rapid increase in hepatic Hg concentration concurrent with the onset of maturity in sharks may result from the continuous intake of Hg via food and the slower growth of mature sharks. The high concentrations of the essential metals Zn and Cu in immature sharks may be explained by the physiological demands related to rapid growth. 相似文献
113.
Chaotic rock units exposed in the upper part of the accretionary complex preserve detailed tectonic information related to the periods before, during, and immediately after accretion. Based on the detailed survey in the upper Miocene Miura–Boso accretionary complex, central Japan, three types of chaotic rock units were identified on the basis of the grain sizes and characteristics of blocks and surrounding matrices. The chaotic rock units composed of silt matrices and sandy to pebbly blocks (Type 3) formed by gravity-driven slumping upon the seafloor. The slumping occurred contemporaneously with deposition of the Misaki and Nishizaki Formations within the Izu–Bonin forearc. Vertical variations in the direction of slump vergence represent successive changes from an initially flat seabed to tilting to the northwest and finally to the southeast. Slumping with a northwest vergence indicates landward tilting of the seafloor immediately prior to accretion, whereas vergence to the southeast reflects oceanward tectonic tilting that occurred once the sediments had crossed the deformation front. Other chaotic rock units that have matrices abundant in sand and pebbles (Types 1, 2) formed as a result of subsurface liquefaction and injection associated with large earthquakes that occurred during and after accretion of the sediments. These chaotic rock units are useful in examining surface/subsurface changes such as tectonic tilting of the seafloor and earthquake events during the initial accretion process. 相似文献
114.
Kwadwo Ansong Asante Tetsuro Agusa Reiji Kubota Hiroko Mochizuki Shuhei Nishida Suguru Ohta Annamalai Subramanian 《Marine pollution bulletin》2010,60(9):1560-1570
Trace elements (TEs) and stable isotope ratios (δ15N and δ13C) were analyzed in fish from deep-water of the Sulu Sea, the Celebes Sea and the Philippine Sea. Concentrations of V and Pb in pelagic fish from the Sulu Sea were higher than those from the Celebes Sea, whereas the opposite trend was observed for δ13C. High concentrations of Zn, Cu and Ag were found in non-migrant fish in deep-water, while Rb level was high in fish which migrate up to the epipelagic zone, probably resulting from differences in background levels of these TEs in each water environment or function of adaptation to deep-water by migrant and non-migrant species. Arsenic level in the Sulu Sea fish was positively correlated with δ15N, indicating biomagnification of arsenic. To our knowledge, this is the first study on relationship between diel vertical migration and TE accumulation in deep-water fish. 相似文献
115.
Kenji Ohta Kei Hirose Masahiro Ichiki Katsuya Shimizu Nagayoshi Sata Yasuo Ohishi 《Earth and Planetary Science Letters》2010,289(3-4):497-502
The electrical conductivities of natural pyrolitic mantle and MORB materials were measured at high pressure and temperature covering the entire lower mantle conditions up to 133 GPa and 2650 K. In contrast to the previous laboratory-based models, our data demonstrate that the conductivity of pyrolite does not increase monotonically but varies dramatically with depth in the lower mantle; it drops due to high-spin to low-spin transition of iron in both perovskite and ferropericlase in the mid-lower mantle and increases sharply across the perovskite to post-perovskite phase transition at the D″ layer. We also found that the MORB exhibits much higher conductivity than pyrolite. The depth–conductivity profile measured for pyrolite does not match the geomagnetic field data below about 1500-km depth, possibly suggesting the existence of large quantities of subducted MORB crust in the deep lower mantle. The observations of geomagnetic jerks suggest that the electrical conductivity may be laterally heterogeneous in the lowermost mantle with high anomaly underneath Africa and the Pacific, the same regions as large low shear-wave velocity provinces. Such conductivity and shear-wave speed anomalies are also possibly caused by the deep subduction and accumulation of dense MORB crust above the core–mantle boundary. 相似文献
116.
Yasunori Mahara Tomoko Ohta Tomochika Tokunaga Hiroyuki Matsuzaki Eiji Nakata Yuki Miyamoto Yukihiro Mizuochi Toshiharu Tashiro Masahiro Ono Toshifumi Igarashi Keisuke Nagao 《Applied Geochemistry》2012
Fifty-three samples, including brines associated with oil and natural gas reservoirs and groundwater samples from deep boreholes, were collected from the Pacific and Japan Sea coastal regions in Japan. The 129I/127I and 36Cl/Cl ratios, and stable isotopes (δD and δ18O) are compared to investigate differences related to the geotectonic settings of the two regions. The δD and δ18O data indicate that brine and groundwater from the Pacific coastal region reflect mixing of meteoric water with connate seawater in the pores of sedimentary rocks. On the other hand, brine and groundwater from the Japan Sea coastal region have been hydrothermally altered. In particular, brines associated with petroleum accumulations at Niigata and Akita showed the same isotopic characteristics as fluids found in the Kuroko deposits of the Green Tuff region in northeastern Japan. There is little difference in the 36Cl/Cl ratios in brine and groundwater from the Pacific and Japan Sea coasts. Most brine and some deep groundwater, except those from the Pleistocene Kazusa Group, have already reached the average secular equilibrium ratio of 9.9 ± 2.7 × 10−15 for their mudstone and sandstone reservoirs. There was no correlation between the 36Cl/Cl ratios and differences in geotectonic setting between the Pacific and the Japan Sea coast. The molar I/Br ratio suggests that the I in all of water samples was of biogenic origin. The average 129I/127I ratio was 290 ± 130 × 10−15 to 294 ± 105 × 10−15 in both regions, showing no relationship to the different geotectonic settings. The uncontaminated brine and groundwater samples are likely to have retained the original 129I/127I ratios of marine I released from the old organic matter stored in sedimentary rock. 相似文献
117.
Tsuyoshi Iizuka Malcolm T. McCulloch Tsuyoshi Komiya Takazo Shibuya Kenji Ohta Haruka Ozawa Emiko Sugimura Kenneth D. Collerson 《Contributions to Mineralogy and Petrology》2010,160(6):803-823
Mt. Narryer and Jack Hills meta-sedimentary rocks in the Narryer Gneiss Complex of the Yilgarn Craton, Western Australia are
of particular importance because they yield Hadean detrital zircons. To better understand the tectonothermal history and provenance
of these ancient sediments, we have integrated backscattered scanning electron images, in situ U–Pb isotopic and geochemical
data for monazites from the meta-sediments. The data indicate multiple periods of metamorphic monazite growth in the Mt. Narryer
meta-sediments during tectonothermal events, including metamorphism at ~3.3–3.2 and 2.7–2.6 Ga. These results set a new minimum
age of 3.2 Ga for deposition of the Mt. Narryer sediments, previously constrained between 3.28 and ~2.7 Ga. Despite the significant
metamorphic monazite growth, a relatively high proportion of detrital monazite survives in a Fe- and Mn-rich sample. This
is likely because the high Fe and Mn bulk composition resulted in the efficient shielding of early formed monazite by garnet.
In the Jack Hills meta-sediments, metamorphic monazite growth was minor, suggesting the absence of high-grade metamorphism
in the sequence. The detrital monazites provide evidence for the derivation of Mt. Narryer sediments from ca. 3.6 and 3.3 Ga
granites, likely corresponding to Meeberrie and Dugel granitic gneisses in the Narryer Gneiss Complex. No monazites older
than 3.65 Ga have been identified, implying either that the source rocks of >3.65 Ga detrital zircons in the sediments contained
little monazite, or that >3.65 Ga detrital minerals had experienced significant metamorphic events or prolonged sedimentary
recycling, resulting in the complete dissolution or recrystallization of monazite. 相似文献
118.
An integrated model simulating the initiation and motion of earthquake and rain induced rapid landslides and its application to the 2006 Leyte landslide 总被引:10,自引:7,他引:3
Kyoji?SassaEmail author Osamu?Nagai Renato?Solidum Yoichi?Yamazaki Hidemasa?Ohta 《Landslides》2010,7(3):219-236
A gigantic rapid landslide claiming over 1,000 fatalities was triggered by rainfalls and a small nearby earthquake in the
Leyte Island, Philippines in 2006. The disaster presented the necessity of a new modeling technology for disaster risk preparedness
which simulates initiation and motion. This paper presents a new computer simulation integrating the initiation process triggered
by rainfalls and/or earthquakes and the development process to a rapid motion due to strength reduction and the entrainment
of deposits in the runout path. This simulation model LS-RAPID was developed from the geotechnical model for the motion of landslides (Sassa 1988) and its improved simulation model (Sassa et al. 2004b) and new knowledge obtained from a new dynamic loading ring shear apparatus (Sassa et al. 2004a). The examination of performance of each process in a simple imaginary slope addressed that the simulation model well simulated
the process of progressive failure, and development to a rapid landslide. The initiation process was compared to conventional
limit equilibrium stability analyses by changing pore pressure ratio. The simulation model started to move in a smaller pore
pressure ratio than the limit equilibrium stability analyses because of progressive failure. However, when a larger shear
deformation is set as the threshold for the start of strength reduction, the onset of landslide motion by the simulation agrees
with the cases where the factor of safety estimated by the limit equilibrium stability analyses equals to a unity. The field
investigation and the undrained dynamic loading ring shear tests on the 2006 Leyte landslide suggested that this landslide
was triggered by the combined effect of pore water pressure due to rains and a very small earthquake. The application of this
simulation model could well reproduce the initiation and the rapid long runout motion of the Leyte landslide. 相似文献
119.
Diamond-bearing carbonate rocks from Kumdy-Kol, Kokchetav massif, Kazakhstan, were strongly altered by fluids flowing through fractures and infiltrating along grain boundaries during exhumation. Alteration includes retrogradation of high-grade silicate assemblages by hydrous minerals, replacement of diamond by graphite and of dolomite by calcite. Diamond-bearing carbonate rocks are among the most intensely altered isotopically with δ18OVSMOW values as low as +9‰, δ13CVPDB=−9‰, and 87Sr/86Sr as high as 0.8050. Evidence of isotopic equilibration between coexisting dolomite and high-Mg calcite during ultrahigh-pressure metamorphism (UHPM) is preserved only rarely in samples isolated from infiltrating fluids by distance from fractures. Isotopic heterogeneity and isotopic disequilibrium are widespread on a hand-specimen scale. Because of this lack of homogeneity, bulk analyses cannot provide definitive measurements of 13C/12C fractionation between coexisting diamond and carbonate. Our study adequately documents alteration on a scale commensurate with observed vein structures. But, testing the hypothesis of metamorphic origin of microdiamonds has not fully succeeded because our analytical spatial resolution, limited to 0.5 mm, is not small enough to measure individual dolomite inclusions or individual diamond crystals. 相似文献
120.
湖南康家湾铅锌金银矿床位于南岭成矿带北部中段,是水口山矿田内发现较晚的大型隐伏矿床.该矿床的矿物组合及矿化特征复杂,前人对其成矿流体特征及成因类型存在不同认识.文章通过野外地质调查和矿物矿相学研究发现该矿床的热液成矿阶段较多,方铅矿主要形成于早期闪锌矿与晚期闪锌矿之间,而金和银的成矿阶段分别与早期闪锌矿和方铅矿趋于一致... 相似文献