Large‐scale folding in the Asemi‐gawa region of the Sanbagawa Belt,southwest Japan     

Hiroshi Mori  Simon Wallis 《Island Arc》2010,19(2):357-370

The Sanbagawa Belt generally shows higher metamorphic grade at higher structural levels. This inversion can be interpreted as reflecting an original inverted thermal structure typical of subduction zone environments. However, repetitions in the distribution of the metamorphic zones seen in central Shikoku, Japan, clearly show the original thermal structure has been affected by deformation after the peak of metamorphism. This repetition has been attributed to both the action of tectonic discontinuities and regional folding. It is important to distinguish between these two interpretations to determine the extent to which the original subduction zone sequence is preserved. Analyses of lithological and structural data reveal the presence of a large‐scale post‐metamorphic fold in the central part of the highest grade region. This folding has an axis that coincides with the thermal axis implied by the distribution of the metamorphic zonation, suggesting the repetition of metamorphic zones in this area can be accounted for by folding without the need for major discontinuities.  相似文献   

Impacts of the Nakhodka heavy-oil spill on an intertidal ecosystem: an approach to impact evaluation using geographical information system     

Teruhisa K  Masahiro N  Hiroshi K  Tomoko Y  Kouichi O;Marine Life Research Group of Takeno 《Marine pollution bulletin》2003,47(1-6):99-104

A major heavy-oil spill from the Russian tanker Nakhodka occurred in the Sea of Japan on 2 January 1997. We investigated the impacts of this spill on a rocky intertidal ecosystem along the southern coast of the Sea of Japan. We selected Imago-Ura Cove as our study site to observe temporal changes along the oiled shore, because minimal cleaning effort was made in this area. Field surveys were conducted every autumn and spring from 1997 to 2000. We measured coverage by macroalgae in 1 x 1-m(2) quadrats and counted the animals in 5 x 5-m(2) quadrats along the intertidal zone. Changes in the ecosystem caused by the oil spill were analyzed by applying a geographical information system (GIS) to the Sea of Japan for the first time. The GIS showed that following the accident there were heavily oiled areas in sheltered regions, but these decreased over the three years. It also showed that coverage by macroalgae and the number of animals increased, although some species of algae with microscopic sporophyte generations, and some populations of perennial shellfish, remained stable or decreased during the study period. GIS was able to trace temporal changes in intertidal communities resulting from the impacts of heavy oil on flora and fauna at a spatial scale of 10-100 m. GIS is thus a practical tool for visualizing, analyzing, and monitoring changes in an ecosystem polluted by oil, taking into account topographic differences along the coastline.  相似文献   

Acoustic backscattering from a sandy seabed     

Ohkawa  K. Yamaoka  H. Yamamoto  T. 《Oceanic Engineering, IEEE Journal of》2005,30(4):700-708

Acoustic backscattering from a sandy seabed was measured at a frequency of 5.5 kHz at a wide range of grazing angles. The measurement system used was the University of Miami's sonar tower, consisting of an omni-directional broadband source and two 16-channel hydrophone receiver arrays. A volume scattering model, which combines a fluid model with reflection/transmission coefficients derived from the Biot theory, is used. This model allows energy penetration into the bottom, calculations of the volume scattering at all grazing angles, and the frequency dependence of the sound speed in the water-saturated sediment. In the model, rather than assume sound-speed correlation length in sedimentary volume, core data were used to assimilate a 3-D fluctuation spectrum of the density. The numerical results showed excellent agreement with the measurement at lower grazing angles. We concluded that the interface roughness scattering was dominant at lower grazing angles, while the volume scattering is dominant at higher grazing angles at the sandy site. The border of the dominance of the interface and volume scattering was the so-called critical angle at this frequency. The frequency dependence of sound speeds is also discussed.  相似文献   

Velocity distributions of high-velocity ejecta from regolith targets     

Satoru Yamamoto  Toshihiko Kadono  Takafumi Matsui 《Icarus》2005,178(1):264-273

We measured the velocity distributions of impact ejecta with velocities higher than ∼100 m s⁻¹ (high-velocity ejecta) for impacts at variable impact angle α into unconsolidated targets of small soda-lime glass spheres. Polycarbonate projectiles with mass of 0.49 g were accelerated to ∼250 m s⁻¹ by a single-stage light-gas gun. The impact ejecta are detected by thin aluminum foils placed around the targets. We analyzed the holes on the aluminum foils to derive the total number and volume of ejecta that penetrated the aluminum foils. Using the minimum velocity of the ejecta for penetration, determined experimentally, the velocity distributions of the high-velocity ejecta were obtained at α=15°, 30°, 45°, 60°, and 90°. The velocity distribution of the high-velocity ejecta is shown to depend on impact angle. The quantity of the high-velocity ejecta for vertical impact (α=90°) is considerably lower than derived from a power-law relation for the velocity distribution on the low-velocity ejecta (less than 10 m s⁻¹). On the other hand, in oblique impacts, the quantity of the high-velocity ejecta increases with decreasing impact angle, and becomes comparable to those derived from the power-law relation. We attempt to scale the high-velocity ejecta for oblique impacts to a new scaling law, in which the velocity distribution is scaled by the cube of projectile radius (scaled volume) and a horizontal component of impactor velocity (scaled ejection velocity), respectively. The high-velocity ejecta data shows a good correlation between the scaled volume and the scaled ejection velocity.  相似文献   

Announcement     

Eiichi Tahara  Wataru Yasui  Hiroshi Yokozaki 《Solar physics》1989,119(2):421-421

  相似文献   

Symplectic integrators and their application to dynamical astronomy     

Hiroshi Kinoshita  Haruo Yoshida  Hiroshi Nakai 《Celestial Mechanics and Dynamical Astronomy》1990,50(1):59-71

Symplectic integrators have many merits compared with traditional integrators:  相似文献   

A numerical study of polar ionospheric currents     

Hiroshi Maeda  Koichiro Maekawa 《Planetary and Space Science》1973,21(8):1287-1300

Numerical calculations for the electric current in the polar ionosphere have been made by assuming some realistic distributions of the electric field and conductivity. Two dynamo actions are taken into account; one of which is induced by ionospheric winds and the other by the solar wind. For the solar wind dynamo action, it is found that the secondary polarization field caused by non-uniform distribution of ionospheric conductivity is much larger than the primary field induced by the solar wind, suggesting its important effect on charged particles in the magnetosphere, and that the irrotational current having a source and sink is of the same order of magnitude as the solenoidal current closing its circuit in the ionosphere. It is also found that the solar wind is, in general, more effective than the ionospheric winds in producing polar current systems such as DP 1 and 2, but in some cases the ionospheric winds have a significant effect on the current distribution.  相似文献   

Changes of microbial populations in a ship's ballast water and sediments on a voyage from Japan to Qatar     

Mimura H  Katakura R  Ishida H 《Marine pollution bulletin》2005,50(7):751-757

Colony-forming eutrophic marine microorganisms in ballast water were counted in samples taken on board in 2002 and 2003. In the ballast water in Japan, viable cell numbers were highly variable but not by more than 10(5.1) colony-forming units (CFU)ml(-1) regardless of season. Even when ballast water was discharged offshore, values varied but not by more than 10(5.0) CFUml(-1). The effectiveness of the ballast water exchange was unconfirmed, except for the February 2003 voyage. No microbial colonies were counted in the reloaded ballast water in the high seas on that voyage, which contributed to the reduction of the total number of viable cells sampled in the discharged ballast water at the Ras Laffan port in Qatar. In sediment samples, the values of 10(5.2) - 10(6.0) CFUml(-1) were estimated for all seasons in which voyages took place. The maximum of the marine Vibrio species, 110 CFUml(-1), was observed in the ballast water sample taken in July 2003. The estimated total viable cell numbers in sediments were higher than those counted in the ballast water throughout the experiments, indicating the importance of sediment management as well as ballast water management on vessels traveling from Japan.  相似文献   

Petrological characteristics and volatile content of magma from the 2000 eruption of Miyakejima Volcano, Japan     

Genji Saito  Kozo Uto  Kohei Kazahaya  Hiroshi Shinohara  Yoshihisa Kawanabe  Hisao Satoh 《Bulletin of Volcanology》2005,67(3):268-280

Among the series of eruptions at Miyakejima volcano in 2000, the largest summit explosion occurred on 18 August 2000. During this explosion, vesiculated bombs and lapilli having cauliflower-like shapes were ejected as essential products. Petrological observation and chemical analyses of the essential ejecta and melt inclusions were carried out in order to investigate magma ascent and eruption processes. SEM images indicate that the essential bombs and lapilli have similar textures, which have many tiny bubbles, crystal-rich and glass-poor groundmass and microphenocrysts of plagioclase, augite and olivine. Black ash particles, which compose 40% of the air-fall ash from the explosion, also have similar textures to the essential bombs. Whole-rock analyses show that the chemical composition of all essential ejecta is basaltic (SiO₂=51–52 wt%). Chemical analyses of melt inclusions in plagioclase and olivine phenocrysts indicate that melt in the magma had 0.9–1.9 wt% H₂O, <0.011 wt% CO₂, 0.04–0.17 wt% S and 0.06–0.1 wt% Cl. The variation in volatile content suggests degassing of the magma during ascent up to a depth of about 1 km. The ratio of H₂O and S content of melt inclusions is similar to that of volcanic gas, which has been intensely and continuously emitted from the summit since the end of August 2000, indicating that the 18 August magma is the source of the gas emission. Based on the volatile content of the melt inclusions and the volcanic gas composition, the initial bulk volatile content of the magma was estimated to be 1.6–1.9 wt% H₂O, 0.08–0.1 wt% CO₂, 0.11–0.17 wt% S and 0.06–0.07 wt% Cl. The basaltic magma ascended from a deeper chamber (10 km) due to decrease in magma density caused by volatile exsolution with pressure decrease. The highly vesiculated magma, which had at least 30 vol% bubbles, may have come into contact with ground water at sea level causing the large explosion of 18 August 2000.Editorial responsibility: S. Nakada, T. DuittAn erratum to this article can be found at  相似文献   

Landslide risk evaluation and hazard zoning for rapid and long-travel landslides in urban development areas   总被引：8，自引：6，他引：2  

Kyoji?SassaEmail author  Gonghui?Wang  Hiroshi?Fukuoka  Fawu?Wang  Takahiro?Ochiai  Masanori?Sugiyama  Tatsuo?Sekiguchi 《Landslides》2004,1(3):221-235

Risk evaluation for earthquake-induced rapid and long-travel landslides in densely populated urban areas is currently the most important disaster mitigation task in landslide-threatened areas throughout the world. The research achievements of the IPL M-101 APERITIF project were applied to two urban areas in megacities of Japan. One site is in the upper slope of the Nikawa landslide site where previous movements were triggered by the 1995 Hyogoken-Nambu earthquake. During detailed investigation, the slope was found to be at risk from a rapid and long-travel landslide induced by sliding surface liquefaction by earthquakes similar in scale to the 1995 event. A new plan to prevent the occurrence of this phenomenon was proposed and the plan was implemented. Another area is the Tama residential area near Tokyo. A set of field and laboratory investigations including laser scanner, geological drilling and ring-shear tests showed that there was a risk of sliding surface liquefaction for both sites. A geotechnical computer simulation (Rapid/LS) using the quantitative data obtained in the study allowed urban landslide hazard zoning to be made at individual street level.  相似文献