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1.
1 IntroductionAnicecoreobtainedfrom polarglaciersoricesheetsisoneofthemostimportantarchivestoreconstructpaleoclimaticandpaleoatmosphericcondition .Informationonpale o environmentcanbeextractedfromicecoresaschemicaland/orphysicalsignals.Amongthechemicalsignals,heavymetalsarenotedassignalsofterrestrialenvironmentalchangeandanthropogenicpollution (e.g .Murozumietal.1 969;NgandPatterson 1 981 ;Hongetal.1 994) .SinceconcentrationsofmostofthemetalsinpolarsnowincentralGreen landareatorbelowthepptl… 相似文献
2.
Current measurements in the surface layer in Sagami and Suruga Bays showed existence of significant tidal currents which are considered to be mainly due to internal tides (Inaba, 1982; Ohwaki,ea al., 1991). In addition, the prevailing period of the tidal currents is semidiurnal in Sagami Bay, but diurnal in Suruga Bay. To explain this difference in the prevailing, periods, numerical experiments were carried out using a two layer model. The internal tides are generated on the Izu Ridge outside the two bays. The semidiurnal internal tide propagates into Sagami Bay having characteristics of an internal inertia-gravity wave, while it propagates into Suruga Bay having characteristics of either an internal inertia-gravity wave or an internal Kelvin wave. The diurnal internal tide behaves only as an internal Kelvin wave, because the diurnal period is longer than the inertia period. Thus, the diurnal internal tide generated on the Izu Ridge can be propagated into Suruga Bay, while it cannot propagate into the inner region of Sagami Bay, though it is trapped around Oshima Island, which is located at the mouth of Sagami Bay. The difference in the propagation characteristics between the semidiurnal and diurnal internal tides can give a mechanism to explain the difference in the prevailing periods of the internal tides between Sagami and Suruga Bays. 相似文献
3.
Surface temperature data obtained in and out of the bay all year round from March 1990 through February 1991, except from July through October 1990 were analyzed to investigate seasonal variability of theKyucho in Sukumo Bay, southwest of Shikoku, Japan. TheKyucho periodically occurs in the bay during both the warming period of March through June and the cooding period of November through February. The onset period of theKyucho is 8–15 days during the warming period and 4–14 days during the cooling period, giving an average of about 10 and 8 days, respectively. The position of the Kuroshio axis offshore in the south of Cape Ashizuri-misaki is a significant factor with theKyucho in the bay. Thermal infrared images taken by the NOAA-11 in the sea off east of Kyushu were also analyzed during the two observation periods. It is clearly found that a warm filament derived from the Kuroshio (KWF) advects northeast to Cape Ashizurimisaki along the Kuroshio, then encounters the southwest coast of Shikoku, followed by inducing theKyucho in the bay by the warm water intrusion. The alongshelf dimension of the KWFs is approximately 50–100 km, and the cross-shelf distance from the western edge of the KWFs to that of the body of the east Kuroshio is about 30–50 km. The KWF sometimes closely approaches to the east coast of Kyushu. An onshore meander of the Kuroshio front around Cape Toimisaki might grow into a KWF in the sea off east of Kyushu. 相似文献
4.
Mjelde Rolf Fjellanger Jan Petter Digranes Per Kodaira Shuichi Shimamura Hideki Shiobara Hajime 《Marine Geophysical Researches》1997,19(1):81-96
A 140 km long wide-angle seismic profile has been acquired by use of 6 Ocean Bottom Seismographs across the Jan Mayen Ridge, North Atlantic. The profile was acquired twice; once with a traditionally tuned standard source and secondly with a somewhat smaller source tuned on the first bubble pulse. Analysis of the frequency content of the data reveals that the single-bubble source within the 10-15 Hz frequency range generates a signal with a level about 5 db above that of the standard source. These differences can partly be related to differences in airgun depth. The higher output level for these frequencies enables the single-bubble source to resolve intra-crustal structures with a higher degree of certainty, when compared to the data acquired by use of the standard source array. The standard source seems to generate slightly more energy for frequencies around 6 Hz, probably due to the use of a large 1200 in/sup3 gun in this array. These low frequencies a re of importance for mapping of lower crustal and upper mantle structures, and it is recommended that this is taken into account when seismic sources for mapping of deep crustal and upper mantle structures are designed. 相似文献
5.
Performance of Mortar and Chemical Grout Injection into Surrounding Soil When Slurry Pipe-jacking Method is Used 总被引:1,自引:0,他引:1
Hideki Shimada Takashi Sasaoka Saeid Khazaei Yasuhiro Yoshida Kikuo Matsui 《Geotechnical and Geological Engineering》2006,24(1):57-77
Small-diameter shallow tunnels are often being built by using the slurry pipe-jacking method. This system involves the pushing
or thrusting of a drivage machine and concrete pipes into the ground. Chemical grout injection into the surrounding soil around
the tunnel is carried out after the drivage and pushing processes are finished. The purpose of the chemical grout injection
is to maintain permanent stability of the surrounding soil. However, the behavior of the chemical grouting material in the
surrounding soil around the tunnel and the amount of optimum injection is not clearly understood. From these points of view,
this paper discusses the performance of the chemical grouting material, when it is injected into the surrounding soil around
the tunnel, by means of 2-D Eulerian–Lagrangian seepage analysis. Moreover, the effectiveness of the chemical grout injection
was evaluated by using the non-linear finite element method. This investigation show when the range of the grouted zone is
designed; it is necessary that the relationship between Young’s modulus of the soil/grouted zone and the confining stress
be taken into consideration in order to establish effective, economical and safe chemical grout injection system. Understanding
the performance of the seepage/dispersion behavior of the chemical grout and the characteristics of soil/ grouted zone is
also important. 相似文献
6.
Monitoring of Over Cutting Area and Lubrication Distribution in a Large Slurry Pipe Jacking Operation 总被引:1,自引:0,他引:1
Saeid Khazaei Hideki Shimada Takashi Kawai Junichi Yotsumoto Kikuo Matsui 《Geotechnical and Geological Engineering》2006,24(3):735-755
Slurry pipe jacking was firmly established as a special method for the non-disruptive construction of the underground pipelines
of sewage systems. Pipe jacking, in its traditional form, has occasionally been used for short railways, roads, rivers, and
other projects. Basically the system involves the pushing or thrusting of concrete pipes into the ground by a number of jacks.
In slurry pipe jacking, during the pushing process, mud slurry and lubricant are injected into the face and the over cutting
area that is between the concrete pipes and the surrounding soil. Next, the slurry fills voids and the soil stabilizes due
to the created slurry cake around the pipes. Fillings also reduce the jacking force or thrust during operation. When the drivage
and pushing processes are finished, a mortar injection into the over cutting area is carried out in order to maintain permanent
stability of the surrounding soil and the over cutting area. Successful lubrication around the pipes is extremely important
in a large diameter slurry pipe jacking operation.
Control of lubrication and gaps between pipes and soil can prevent hazards such as surface settlement and increases in thrust.
Also, to find voids around the pipes after the jacking process, in order to inject mortar for permanent stabilizing, an investigation
around the pipes is necessary. To meet these aims, this paper is concerned with the utilization of known methods such as the
GPR (Ground Penetrating Radar) system and borehole camera to maintain control of the over cutting area and lubricant distribution
around the pipes during a site investigation. From this point of view, experiments were carried out during a tunnel construction
using one of the largest cases of slurry pipe jacking in Fujisawa city, Japan. The advantages and disadvantages of each system
were clarified during the tests. 相似文献
7.
Rock burst prediction is a worldwide challenge that we have long tried to overcome. This study tentatively proposed a method to regionally predict rock burst hazards using microseismic energy attenuation. To verify the feasibility of the proposal, first, the mechanism of microseismic energy propagation and attenuation in rock medium was explored, and dominant attenuation characteristics of microseismic waves were analyzed. Second, a spatial attenuation model of microseismic energy was established, and the average energy attenuation coefficient for each wave path was defined. A 3D seismic energy attenuation inversion algorithm was put forward, and the corresponding computation matrix was developed. Third, a continuous microseismic field investigation was carried out in a deep coal mine. Seismic energy attenuation coefficient was confirmed using the calibrated focus position and energy determination. Based on data discretization processing, energy attenuation inversion and tomography, potential rock burst hazard regions were strictly zoned in mining areas. Finally, regional prediction results obtained from the microseismic energy attenuation were compared with the direct measurement results obtained from the classical drilling dust method to verify the reliability of proposed approach. It turns out that rock burst hazard regions predicted by the microseismic energy attenuation agreed well with the objective hazardous situations. Seismic energy attenuation coefficient is a significant evaluation factor that directly mirrors the inelastic performance of rock medium. Energy attenuation coefficient threshold used for determining the rock burst hazard regions was 3.0 km?1. Reliability of the seismic energy attenuation inversion and tomography was closely related to the spatial distribution of microseisms in a localized region. The optimum spatial density of microseisms was 0.2 m?3. Regional rock burst prediction using microseismic energy attenuation is an effective approach for revealing potential hazardous regions in deep mining conditions. This approach improves the pertinence of geological hazard prevention and provides a beforehand reference for targeted hazard management. 相似文献
8.
Akio Tamaki Ayumi Nakaoka Hideki Maekawa Fumihiko Yamada 《Estuarine, Coastal and Shelf Science》2008,78(4):727-738
The fishery yield of Manila clams, Ruditapes philippinarum, increased considerably in the 1970s but has decreased rapidly since the middle 1980s on extensive intertidal sand flats in Ariake Sound (Kyushu, Japan). A survey conducted in 2004 on a 3.4-km2 sand flat located in the central part of the Sound (Shirakawa sand flat) revealed four dominant species: two thalassinidean shrimps (Upogebia major and Nihonotrypaea japonica), which are deep-reaching burrow dwellers with strong bioturbation activities, and two bivalves (Mactra veneriformis and R. philippinarum). All four species belong to a phytoplankton (diatom)-feeding guild. In the late 1970s, the Manila clam population prevailed in high densities over the entire sand flat, whereas its distribution was restricted to the lowest quarter of the shore in 2004. In contrast, the population sizes and zones of occurrence of the other phytoplankton feeders have expanded in the absence of R. philippinarum, perhaps an indication of competitive release. After establishment, effects of the thalassinidean shrimps on sediment stability appear to have further reduced clam abundances. Across the sand flat in 2004, wet weight population biomass estimates for N. japonica, U. major, M. veneriformis, and R. philippinarum (whole body for shrimps and soft tissue for bivalves) were 304, 111, 378, and 234 tonnes, respectively. Based on Manila clam fishery yield records from Shirakawa, the carrying capacity of the Shirakawa sand flat in the late 1970s was estimated to be two times greater than the sum value for the whole phytoplankton-feeding guild in 2004. It is hypothesized that (1) the amount of phytoplankton determines the carrying capacity for the benthic community on the Shirakawa sand flat, with both phytoplankton and benthic biomass at maxima in the late 1970s, and (2) the subsequent increases in competition for space have caused further declines in the Manila clam population biomass to approximately one-eighth of its past value. 相似文献
9.
10.