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31.
The possible influences of the Emperor Seamounts (ESs) upon the subarctic gyre of the North Pacific (NPSAG) were investigated
by a series of numerical experiments. In the experiments, a two-layer ocean with a meridional mountain ridge was forced by
seasonally varying wind stress. We focused on how the return ratio, the ratio of the boundary transport along the eastern
side of the ridge to the interior Sverdrup transport, changes with ridge height, width and density stratification. It was
found that the return ratio can be large if the ridge width is greater than the width of the viscous boundary layer. In this
case, the bottom pressure torque determines the return ratio; the return ratio is almost proportional to the ridge height
when the ridge height is small and some contours of planetary potential vorticity pass over the ridge. However, the return
ratio is independent of the ridge height and decreases with the stratification when the ridge height is large and all the
contours of planetary potential vorticity are closed. These dependences of the return ratio were understood in terms of barotropic
and baroclinic components of the bottom pressure torque. Implications for the bathymetric influences of ESs on the actual
NPSAG are also discussed. 相似文献
32.
In this study, we report the elastic properties of three ultrahigh-pressure phases of SiO2: pyrite, cotunnite and Fe2P types between 300 and 1,500 GPa calculated by means of the density functional ab initio method. It is generally thought
that materials tend to be more compact and isotropic with increasing pressure. These three ultrahigh-pressure phases of silica
are mechanically stable in the investigated pressure range according to the Born criteria, while the cotunnite and Fe2P types are unstable at lower pressure. The elastic azimuthal anisotropy of these ultrahigh-pressure phases of silica shows
that all the structures counterintuitively have considerable anisotropies even at multimegabar pressures. Among the three
investigated structures, the cotunnite type of SiO2 is the most elastically anisotropic phase due to a soft compression along the b axis combined with a large distortion of the polyhedrons that make the structure. This might also be related to its thermodynamic
unfavorability compared to the Fe2P type under extreme pressure condition. The bond property analyses clearly show that the Si–O bond remains an ionic-covalent
mixed bond even at multimegabar pressures with an invariable ionicity with pressure. This argument can explain the monotonously
pressure dependence of the elastic anisotropy in the case of pyrite, while the changes in the velocity distribution patterns
out of the thermodynamic instability range largely contribute to those of the cotunnite and Fe2P types. 相似文献
33.
34.
Taku Kitajima Yoji Kobayashi Ryuji Ikeda Yoshihisa Iio Kentaro Omura 《Island Arc》2001,10(3-4):318-325
Abstract Terrestrial heat flow at Hirabayashi in Awaji Island, south-west Japan, was investigated using the deep borehole penetrating through the Nojima Fault, which was activated during the 1995 Hyogo-ken Nanbu earthquake, by measuring the thermal conductivity of basement rocks. Using the temperature logging data, the value of terrestrial heat flow in Hirabayashi was found to be 56.6 ± 5.2 mW/m2 . The relationship between cut-off depth of aftershocks of the Hyogo-ken Nanbu earthquake in Hirabayashi and terrestrial heat flow are discussed. The cut-off depth roughly corresponds to isotherms of 300°C. 相似文献
35.
We derive a set of non-hypersingular boundary integral equations, both elastodynamic and elastostatic, for the analysis of arbitrarily shaped 2-D anti-plane and in-plane cracks located in an infinite homogeneous isotropic medium, rendered in a unified nomenclature for all cases. The hypersingularities that appear in the usual formulations for the dynamic cases, existent both at the source point and at the wavefront, are removed by way of a regularization technique based on integration by parts. The equations for the in-plane cases are presented in terms of a local Cartesian coordinate system, one of the axes of which is always held locally tangential to the crack trace. The expressions for the elastic field at any point on the model plane are also given.
Our formulations are shown to yield accurate numerical results, as long as appropriate stabilization measures are taken in the numerical scheme. The numerical applicability of our method to non-planar crack problems is illustrated by simulations of dynamic growth of a hackly crack which has small off-plane side-branches. The results imply that the branching of a crack brings about a significant decrease in the crack-tip stress concentration level and consequently may play an essential role in the arrest of earthquake rupturing. 相似文献
Our formulations are shown to yield accurate numerical results, as long as appropriate stabilization measures are taken in the numerical scheme. The numerical applicability of our method to non-planar crack problems is illustrated by simulations of dynamic growth of a hackly crack which has small off-plane side-branches. The results imply that the branching of a crack brings about a significant decrease in the crack-tip stress concentration level and consequently may play an essential role in the arrest of earthquake rupturing. 相似文献
36.
We examined the characteristics of landslides triggered by the 2016 Kumamoto earthquake (Mw = 7.0: focal depth=10.0 km) in forests and grasslands within two affected watersheds (Tokosegawa: 6.9 km2 and Nigorigawa: 6.1 km2) in southwestern Japan. We identified 190 landslides using aerial photographs and analyzed their sizes by geographic information system (GIS). Field investigations were conducted to obtain landslide depth, volume and residual sediment for 38 selected landslides (21 in forests and 17 in grasslands). The minimum area of detected landslides in grasslands (400 m2) was smaller than in forests (1000 m2), probably because of reduced detectability of landslides under tree cover. The ratio of total area occupied by landslides for a given range of slope gradient in the watersheds increased from 3.2% on gentle grassland slopes (10–15°) to 15.5% on steep (>45°) slopes, whereas the maximum landslide-area ratio in forest sites (7.4%) occurred on relatively gentle slopes (25–30°). Estimated landslide volume ranged from 27 to 9622 m3, based on mean depth of each landslide measured around individual landslide scars. Moreover, the volumetric ratio of landslide deposit volume to total landslide volume exceeded 100% for 48% of the landslides within forests and 35% of the landslides within grasslands. Our findings show that land cover had extensive and recognizable effects on the characteristics of landslides and resulting in-channel sediment accumulations. Resetting sediment dynamics after earthquakes associated with different land cover distributions needs to be considered within watersheds. © 2019 John Wiley & Sons, Ltd. 相似文献
37.
Tillage practice has received much attention due to its effects on greenhouse gas emissions from agricultural fields. The understanding of carbon mineralization associated with soil aggregates helps to explore the influence mechanisms of tillage practice on soil carbon dynamics. Total carbon and carbon mineralization rates associated with various sizes of soil aggregates under no-tillage and tillage treatments were studied with a volcanic ash soil. Total carbon content in microaggregates (<0.25 mm) was higher than that in macroaggregates (>0.25 mm) for both the no-tillage and tillage treatments, since microaggregates of the volcanic ash soil include more fine silts and clay particles absorbing more organic agents. The carbon mineralization rate and total carbon were highly correlated (R2 = 0.6552, P = 0.002) for both treatments, suggesting that soil aggregate size is an important factor to influence the carbon mineralization rate. The no-tillage system showed the advantage of improving soil structure for volcanic ash soil. A larger proportion of microaggregates with relatively high carbon mineralization might contribute to the greater carbon loss from tilled soils. Unlike aggregate size, short-term tillage showed no significant effects on carbon mineralization rates associated with aggregates in a specific size class. 相似文献
38.
Yukiyo Saitoh Kenshi Kuma Yutaka Isoda Hiroshi Kuroda Hiromi Matsuura Taku Wagawa Hyoe Takata Naoto Kobayashi Seiya Nagao Takeshi Nakatsuka 《Journal of Oceanography》2008,64(6):815-830
We report measurements of iron, nutrients, dissolved oxygen, humic-type fluorescence intensity and chlorophyll a concentrations in the coastal waters at the inflow (western) and outflow (eastern) ends of Tsugaru Strait (Japan) in June
2003 and 2004. Two different water masses (intensive eastward flow “subtropical Tsugaru Warm Current Water (TWCw)” and weak
westward flow “subarctic Oyashio Water (OW)”) were observed at the eastern end of the strait. TWCw at the southern part of
the eastern strait was vertically homogeneous with a uniform concentrations of iron (0.7–1.1 nM for labile dissolved Fe and
14–20 nM for total dissolvable Fe in 2003) as well as other chemical, biological and physical components throughout the water
column of 200 m due to strong vertical mixing in the strait. The degree of mixing in the Tsugaru Warm Current (TWC) is predominantly
affected by diurnal tidal current, which is strong during the period of tropical tides and weak during the period of equinoctial
ones. The especially strong vertical water mixing in 2003 is caused by large dissipation energy input due to the bottom friction
of passage-flow through the strait and tidal current. At the northern part of the eastern strait, the fresh surface layer
overlying the OW and the deep-bottom waters in 2003 contained large concentrations of dissolved iron, resulting from iron
supplied from river runoff and shelf sediments, respectively. These results suggest that the most important mechanism for
transporting iron in the strait is the strong vertical water mixing due to the tidal current, and that the iron sources in
the coastal waters are the organic-associated, iron-rich freshwater input into the surface water. 相似文献
39.
Wave energy flow in shallow ground depth is calculated based on main shock records obtained at 30 vertical array sites throughout Japan during nine recent strong earthquakes (MJ=6.4–8.0) by assuming vertical propagation of SH waves. It is generally found that upward energy tends to decrease considerably as it goes up from the base (about 100 m deep) to the ground surface. Large energy is reflected at layer boundaries with clear impedance contrast and returns to deeper ground, so that only less than 10–30% of the upward energy at the base level arrives at the ground surface in most sites. Energy dissipation calculated from the upward and downward energies tends to increase with the increase of damping ratio of the ground back-calculated from the seismic records. It is also found that the upward energy at the base may roughly be estimated for engineering purposes using spherical energy radiation of the body wave despite strong effects of fault rupture/path mechanisms. 相似文献
40.
Tomoko Sato Hiroto Takada Takehiko Yagi Hirotada Gotou Taku Okada Daisuke Wakabayashi Nobumasa Funamori 《Physics and Chemistry of Minerals》2013,40(1):3-10
We have investigated the high-pressure behavior of cristobalite in helium by powder X-ray diffraction. Cristobalite transformed to a new phase at about 8 GPa. This phase is supposed to have a molar volume of about 30 % larger than cristobalite, suggesting the dissolution of helium atoms in its interstitial voids. On further compression, the new phase transformed to a different phase which showed an X-ray diffraction pattern similar to cristobalite X-I at about 21 GPa. On the other hand, when the new phase was decompressed, it transformed to another new phase at about 7 GPa, which is also supposed to have a molar volume of about 25 % larger than cristobalite. On further decompression, the second new phase transformed to cristobalite II at about 2 GPa. In contrast to cristobalite, quartz did not show anomalous behavior in helium. The behavior of cristobalite in helium was also consistent with that in other mediums up to about 8 GPa, where the volume of cristobalite became close to that of quartz. These results suggest that dissolution of helium may be controlled not only by the density (amount of voids) but also by the network structure of SiO4 tetrahedra (topology of voids). 相似文献