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41.
Yoshihide Ogasawara Masahito Ohta Kyoka Fukasawa Ikuo Katayama and Shigenori Maruyama 《Island Arc》2000,9(3):400-416
Abstract Dolomite marble from the Kumdy–Kol area of the Kokchetav Massif contains abundant microdiamond, mainly in garnet and a few in diopside. The mineral assemblage at peak metamorphic condition consists of dolomite + diopside + garnet (+ aragonite) ± diamond. Inclusions of very low MgCO3 calcite and almost pure calcite occur in diopside and are interpreted as aragonite and/or aragonite + dolomite. Single-phase Mg–calcite in diopside with a very high MgCO3 component (up to 21.7 mol%) was also found in diamond-free dolomitic marble, and is interpreted as a retrograde product from aragonite + dolomite to Mg–calcite. The dolomite stability constrains the maximum pressure (P) at < 7 GPa using previous experimental data, whereas the occurrence of diamond yields the minimum peak pressure–temperature (P–T) condition at 4.2 GPa and 980 °C at X co 2 = 0.1. The highest MgCO3 in Mg–calcite constrains the minimum P–T condition higher than 2.5 GPa and 800 °C for the exhumation stage. As these marbles were subjected to nearly identical P–T metamorphic conditions, the appearance of diamond in some carbonate rocks was explained by high X co 2 . A low X co 2 condition refers to high oxidized conditions and diamond (and/or graphite) becomes unstable. Difference in X co 2 for marble from the same area suggests local heterogeneity of fluid compositions during ultrahigh-pressure metamorphism. 相似文献
42.
Takahiro Endoh Takeshi Matsuno Yutaka Yoshikawa Eisuke Tsutsumi 《Journal of Oceanography》2014,70(1):81-90
The terms of the steady-state turbulent kinetic energy (TKE) budget in the oceanic convective boundary layer (CBL) are estimated by use of microstructure data obtained over the continental shelf of the East China Sea. The dissipation term is calculated from the micro-scale vertical shear of horizontal velocity measured directly using a freely-falling microstructure profiler, whereas the buoyancy flux and shear production terms are estimated indirectly by integrating vertically the one-dimensional conservation equation of density and by applying similarity theory, respectively. The transport term, calculated as the residual of the other three terms, vertically redistributes the TKE from the upper half of the CBL to the lower half, consistent with the TKE budgets in the atmospheric CBL and in shear-free and slightly-sheared CBLs simulated by large eddy-simulation models. The relatively large contribution of the transport term to the TKE budget shows that a local equilibrium form of the TKE equation is not appropriate for the TKE budget in the oceanic CBL. 相似文献
43.
Yuzo Ohnishi Tomofumi Koyama Ikuo Hagiwara Shigeru Miki Testuya Shimauchi 《Geomechanics and Geoengineering》2014,9(2):97-112
This paper discussed the analytical precision on equations of motion in some practical studies that use 2-D DDA, 2D-Coupled analysis of NMM & DDA, and 3D-DDA. We point out the main reason for numerical instability in DDA is loss of the effective digits when superposing the global stiffness matrix under the variable conditions of large and the small blocks. Categories of analyses are distributed in 2D-DDA static masonry structures such as the Great Pyramid and the Pont du Gard, 2D-DDA dynamic rock fall problems and the sensitivity of its analysis on the velocity ratio and the penalty, earthquake response analysis of rock slopes, 2D-NMM, 2D-coupled analysis of DDA and NMM and 3D-DDA rock fall problem. The selected examples on the Great Pyramid, Pont du Gard and Bayon Temple at Angkor Thom are located in Egypt, France and Cambodia respectively as UNESCO world heritages sites. The authors evaluated the applicability of the methods and the reliability of the results by comparing different methods and site observations from the practical problems. 相似文献
44.
Dynamic analysis of ground with rigorous use of strain dependency and its application to seismic microzonation of alluvial plane 总被引:1,自引:1,他引:0
Seismic microzonation is one of the most important measures to mitigate earthquake hazards in urban areas. Because the ground motion varies significantly with the subsurface geology, it is needed for microzonation to account as much as possible for the local soil conditions. Noteworthy is that nonlinear deformation properties of soil play essential roles in amplification of strong ground motion. It is desired furthermore to focus on the expected damage extent in addition to the calculated maximum acceleration and/or velocity. The present study first developed a computer code for one-dimensional response analysis of ground that reasonably takes into account nonlinear dynamic soil properties. Second, correlations between the calculated ground motion and damage extent were obtained by examining seismic damages during the past earthquakes. By combining these two issues, seismic microzonation was carried out, and detailed damage distribution was assessed. The product of this study covers not only the damage caused by ground shaking but also liquefaction problem and lifeline damage. 相似文献
45.
Experimental Study of Dry Granular Flow and Impact Behavior Against a Rigid Retaining Wall 总被引:7,自引:1,他引:6
Shallow slope failure in mountainous regions is a common and emergent hazard in terms of its damage to important traffic routes and local communities. The impact of dry granular flows consisting of rock fragments and other particles resulting from shallow slope failures on retaining structures has yet to be systematically researched and is not covered by current design codes. As a preliminary study of the impact caused by dry granular flows, a series of dry granular impact experiments were carried out for one model of a retaining wall. It was indirectly verified that the total normal force exerted on a retaining wall consists of a drag force (F d), a gravitational and frictional force (F gf), and a passive earth force (F p), and that the calculation of F d can be based on the empirical formula defined in NF EN Eurocode 1990 (Eurocode structuraux. Base de calcul des structures, AFNOR La plaine Saint Denis, 2003). It was also indirectly verified that, for flow with Froude number from 6 to 11, the drag coefficient (C d) can be estimated using the previously proposed empirical parameters. 相似文献
46.
K. Ohtsuka M. Yoshikawa J. Watanabe E. Hidaka H. Murayama T. Kasuga 《Earth, Moon, and Planets》2008,102(1-4):179-182
We explored the substantial spatial spread of the Quadrantid stream, based on the backward integration of orbital motions
of the Quadrantids, impulsively perturbed by Jupiter. We found that the Jovian impulses can widely spread out them in the
early twentieth century, especially their perihelia extended by a factor of ∼90 than those at the observed epoch. We regarded
the spread as the intrinsic one of the Quadrantid stream itself. 相似文献
47.
This paper presents experimental results of a series of 1g shake table tests on mitigation measures for a model consisting of a 3×3 pile group and a sheet-pile quay wall in which the pile group was subjected to liquefaction-induced lateral spreading. First, general observations associated with the mechanism of lateral spreading and pile response are presented based on tests without remedial measures, followed by in depth discussions. Second, three remedial techniques were deployed to provide an adequate seismic performance of the pile group and the quay wall: (i) mitigating sheet pile of floating type, (ii) mitigating sheet pile of fixed end type, and (iii) anchoring the quay wall to a new pile row. The main objective of these mitigation methods was to restrict ground distortion behind the quay wall, enhancing seismic response of pile group and quay wall. This mitigation philosophy was decided based on the outcome of the first part, which consisted of a series of tests without mitigation measures. In addition, it should be noted that the proposed countermeasures were selected to be applicable for existing vulnerable pile groups, which are at risk of liquefaction and lateral spreading. Results of different mitigation tests are comparatively examined using a parameter called reduction factor, and the effectiveness of each countermeasure is discussed in detail. The results demonstrate that by applying the proposed mitigation measures the seismic performance of both pile group and quay wall can be improved, as a result of reduction in soil displacement and velocity of soil flow. 相似文献
48.
Seda Sendir Torisu Junichi Sato Ikuo Towhata Tsuyoshi Honda 《Soil Dynamics and Earthquake Engineering》2010
This paper concerns technological efforts for the general acceptance of performance-based seismic design principle of geotechnical structures. Among many problems to be solved, a particular emphasis was placed on the prediction of residual displacement that remains after a strong earthquake. Because of the complicated behavior of soils undergoing cyclic loading, the prediction is often either complicated/costly or not very accurate. The aim of this study is to examine the capability of existing prediction measures and propose some future scopes. To achieve these goals, shaking table model tests and laboratory shear tests were conducted by taking fill dams as an example target structure. It is concluded that performance-based design is possible if the necessary time and cost are spent and if the required accuracy of prediction is reasonable. 相似文献
49.
Ryoshi Ishiwatari Koichi Negishi Hiroyasu Yoshikawa Shuichi Yamamoto 《Organic Geochemistry》2009,40(4):520-530
Temporal changes in paleoproductivity of Lake Biwa (Japan) over the past 32 kyr have been studied by analyzing bulk organic carbon and photosynthetic pigments (chlorins) in the BIW95-5 core. Primary productivity was estimated on the assumption of C/Norg values of 8 for autochthonous organic matter (OM) and 25 for allochthonous OM and using an equation developed for the marine environment. The estimate indicates that primary productivity ranges from 50 to 90 g C m?2 yr?1 in the Holocene, while it is ~60 g C m?2 yr?1 on average in the last glacial. Pheophytin a and pheophorbide a are the major chlorins. A downcore profile of chlorin concentration normalized to autochthonous organic carbon (OC) shows a decreasing trend. Chlorin productivity was corrected by removal of the effect of post-burial chlorin degradation. The temporal profile of chlorin productivity thereby obtained resembles that from autochthonous OC.The difference in primary productivity between the Holocene and the glacial for the lake is markedly smaller than that for Lake Baikal situated in the boreal zone. This difference between the two lakes is probably caused by the difference in their climatic conditions, such as temperature and precipitation. Precipitation at Lake Biwa is relatively large during the glacial and the Holocene because of the continuous influence of the East Asian monsoon. Lake Baikal precipitation is generally small as a result of control by the continental (Siberia) climate regime. In addition, a significant difference in productivity between the glacial and the Holocene for Lake Baikal may be essentially controlled by the hydrodynamic systems in the lake.Lake Biwa terrigenous OM input events occurred at least five times over the period 11–32 kyr BP, suggesting enhanced monsoon activity. Molecular examination of the layer with a large input of terrigenous OM during the Younger Dryas indicates that concentrations of terrigenous biomarkers such as n-C27–C31 alkanes, lignin phenols, cutin acids, ω-hydroxy acids and C29 sterols are high, suggesting that soil OM with peat-like material entered the lake as a result of flooding. An enhanced sedimentation rate in the last 3000 years might have been partially caused by agricultural activity around the lake. 相似文献
50.
Takehiko Mori Yasuaki Sudo Tomoki Tsutsui Shin Yoshikawa 《Bulletin of Volcanology》2008,70(9):1031-1042
Isolated-type tremors having two events with different dominant frequencies are characteristic seismological phenomena observed
during the fumarolic activity stage at Aso Volcano. These isolated tremors are called hybrid tremors (HBT) and comprise two
parts: an initial part named the “HF-part” with a dominant frequency in the high-frequency region (approximately 10 Hz) and
the following part named the “LF-part” with a dominant frequency in the low-frequency region (approximately 2 Hz). The LF-part
is observed after the HF-part, and the HBT is accompanied by a long-period tremor (LPT). Hypocenters and source parameters
are estimated using seismograms recorded at 64 stations around Nakadake crater. The amplitude distributions of all HF-parts
have almost similar trends. Similarly, the amplitude distributions of all LF-parts have almost similar trends. However, the
amplitude distributions of HF- and LF-parts are not similar. From these results, we proposed that the hypocenters and source
parameters of HF- and LF-parts are not common, but each of them have common hypocenters and source parameters. The hypocenter
region of HF-parts was estimated to be just beneath the fumarole region south of the 1st crater: the volume fluctuation is
the major source factor. The hypocenter region of LF-parts is estimated to be at a depth of approximately 300 m beneath the
first crater: the strike–slip component is the major source parameter. The hypocentral depth of LF-parts is located at the
upper end of the crack estimated to be the source of the LPTs. The LPTs and HBTs are observed almost simultaneously. We consider
that volcanic fluid is involved in the source mechanisms of both HBT and LPT. 相似文献