Field measurements of absolute gravity in East Antarctica     

Koichiro Doi  Hideaki Hayakawa  Takahito Kazama  Toshihiro Higashi  Shingo Osono  Yoichi Fukuda  Jun Nishijima  Yuichi Aoyama  Junichi Ueda 《极地研究(英文版)》2013,(4):339-343

Abstract This paper reports the results of field-based absolute gravity measurements aimed at detecting gravity change and crustal displacement caused by glacial isostatic adjustment. The project was initiated within the framework of the 53rd Japanese Antarctic Research Expedition （JARE53）. Absolute gravity measurements, together with GPS measurements, were planned at several outcrops along the Prince Olav Coast and S6ya Coast of East Antarctica, including at Syowa Station. Since the icebreaker Shirase （AGB 5003） was unable to moor alongside Syowa Station, operations were somewhat restricted during JARE53. However, despite this setback, we were able to complete measurements at two sites： Syowa Station and Langhovde. The absolute gravity value at the Syowa Station IAGBN （A） site, observed using an FG-5 absolute gravimeter （serial number 210; FG-5 #210）, was 982 524 322.7＋0.1 ktGal, and the gravity change rate at the beginning of 2012 was -0.26 gGal.a-1. An absolute gravity value of 982 535 584.2~0.7 ktGal was obtained using a portable A-10 absolute gravimeter （serial number 017; A-10 #017） at the newly located site AGS01 in Langhovde.  相似文献   

The nature of volcanic earthquake swarm preceding the 2000 flank eruption at Usu volcano, Hokkaido, Japan   总被引：1，自引：0，他引：1  

Vyacheslav M. Zobin  Yuichi Nishimura  Jun'ichi Miyamura 《Geophysical Journal International》2005,163(1):265-275

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Hydraulic and numerical study on the generation of a subaqueous landslide-induced tsunami along the coast   总被引：1，自引：0，他引：1  

Yoshinori Shigihara  Daichi Goto  Fumihiko Imamura  Yuichi Kitamura  Takayuki Matsubara  Kazuaki Takaoka  Kazuhiko Ban 《Natural Hazards》2006,39(2):159-177

By carrying out the hydraulic experiments in a one-dimensional open channel and two-dimensional basin, we clarified the process of how a landslide on a uniform slope causes the generation of a tsunami. The effect of the interactive force that occurs between the debris flow layer and the tsunami is significant in the generation of a tsunami. The continuous flow of the debris into the water makes the wave period of the tsunami short. The present experiments apply numerical simulation using the two-layer model with shear stress models on the bottom and interface, and the results are compared. The simulated debris flow shows good agreement with the measured results and ensures the rushing process into the water. We propose that the model use a Manning coefficient of 0.01 for the smooth slope and 0.015 for the rough slope, and a horizontal viscosity of 0.01 m²/s for the landslide; an interactive force of 0.2 for each layer is recommended. The dispersion effect should be included in the numerical model for the propagation from the shore.  相似文献   

Analysis of runoff generation and soil erosion processes by using environmental radionuclides in semiarid areas of Mongolia   总被引：1，自引：0，他引：1  

Yuichi Onda  Hiroaki Kato  Maki Tsujimura  Dambaravjaa Oyunbaatar 《Journal of Hydrology》2007,333(1):124-132

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Experimental investigation of conditions of lateral shear reinforcements in RC columns accompanied by buckling of longitudinal bars     

Yuichi Sato  HuneBum Ko 《地震工程与结构动力学》2007,36(12):1685-1699

This study presents a cyclic load test of four RC columns to obtain data on stresses and strains on lateral shear‐reinforcing bars that contact buckled longitudinal reinforcing bars. The specimens include columns laterally jacketed with all‐elastic fibre‐reinforced polymer (FRP) sheets. The buckling lengths and modes in the longitudinal bars of the four column specimens stabilized at a buckling deflection (= lateral deformation of buckled longitudinal bar) from 0.3 to 0.6 mm. The yield portion ratio r_by of shear reinforcement around the buckled longitudinal bars was introduced as an index of the development of buckling conditions. Here, the yield portion ratio r_by was defined as the ratio of the length of the region where the shear reinforcements yield l_by, to the buckling length l_b. The r_by values of the tested columns ranged from 0.45 to 0.76. The test results show that the buckling stress and the specific compressive stress of the longitudinal bars in the columns were smaller than those of the bare bars. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Distribution of the geochemical signature caused by the 2011 Tohoku-oki tsunami in Misawa harbor,northern Japan     

Frenken  Mike  Bellanova  Piero  Nishimura  Yuichi  Reicherter  Klaus  Schwarzbauer  Jan 《Natural Hazards》2022,114(1):313-333

Natural Hazards - The 2011 Tohoku-oki tsunami left a characteristic geochemical signature in the sediments of the Misawa harbor on the Aomori coastline (northern Japan), not only in vertical...  相似文献   

Distribution depth of the transforming stage larvae of myctophid fishes in the subtropical–tropical waters of the western North Pacific     

Chiyuki Sassa  Kouichi Kawaguchi  Yuichi Hirota  Minoru Ishida 《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(12):2181-2193

We describe the day–night vertical distribution patterns of 18 species or types of myctophid fish larvae at the transforming stage based on discrete depth sampling from the surface down to 1000-m depth in the subtropical–tropical western North Pacific. A total of 551 transforming stage larvae were collected at the 19 sampling stations. Except for the Diaphus species and Notolychnus valdiviae, all of the transforming stage larvae (including genera Benthosema, Bolinichthys, Centrobranchus, Ceratoscopelus, Diogenichthys, Hygophum, Lampanyctus, Lobianchia, Myctophum, Symbolophorus, and Triphoturus) were collected in the lower mesopelagic zone from 600- to 900-m depth during both day and night, showing no diel vertical migration (DVM). On the contrary, the Diaphus species and N. valdiviae larvae undergo DVM during the transforming stage, occurring below 200-m layer during the daytime and migrating up to the upper 150-m layer at night, i.e., they show earlier adaptation to juvenile–adult behaviors. Most myctophid fish larvae are known to undertake substantial ontogenetic vertical migration (OVM) from the epipelagic to mesopelagic zones during their early life stage. Although considerable sampling effort was carried out in this study, transforming larvae, except for the above two migratory ones, were not collected in the epipelagic and upper mesopelagic zones, strongly suggesting that their sinking speed would be high. It would be advantageous for survival to spend their highly vulnerable transforming stage in the lower mesopelagic zone, where predation pressures are lower and physical conditions are more stable than in the upper layers.  相似文献   

Occurrence of brominated flame retardants, polycyclic musks, and chlorinated naphthalenes in seal blubber from Antarctica: Comparison to organochlorines     

Alessandra Schiavone  Kurunthachalam Kannan  Yuichi Horii  Silvano Focardi  Simonetta Corsolini 《Marine pollution bulletin》2009,58(9):1415-1419

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The height of the maximum ionospheric electron density over the MU radar     

Shun-Rong Zhang  Shoichiro Fukao  William L. Oliver  Yuichi Otsuka 《Journal of Atmospheric and Solar》1999,61(18):361

Ionospheric F₂-layer peak height h_mF₂ variations, as measured over 1986–1995 by the MU radar (34.85°N, 136.1°E) and as calculated with a theoretical model, are discussed. The diurnal variations of the measured peak height for different seasons and levels of solar activity are compared with those estimated from ionosonde M3000F₂ and IRI predictions. Also given are the measured ion drift velocities and meridional neutral winds needed to understand the dynamic behavior of the F₂-layer. It is found that: (1) h_mF₂ is generally higher during periods of the solar maximum than during periods of the solar minimum, and higher in summer than in winter; (2) for the solar maximum, h_mF₂ drops markedly in the morning and in the afternoon, while, for the solar minimum, the h_mF₂ minimum occurs in the morning during summer and usually in the afternoon during winter. In general, the measured h_mF₂ is well reproduced by our model when we use the observed drift velocities and plasma temperatures as inputs. Our modeling study shows that the neutral wind contributes strongly to the diurnal variation of h_mF₂ in winter by lowering the ionization layer by day, particularly for the solar maximum; it also helps to enlarge the day–night difference of h_mF₂ in summer. The northward electromagnetic drifts that usually cancel the neutral wind effect have only a minor effect for the location of the MU radar. Other features of the observed h_mF₂ variations, e.g., the solar maximum–minimum difference, the summer–winter difference, and the morning and afternoon drops, are explained by the basic processes of O⁺ production, loss and diffusion, as influenced by the atomic oxygen concentration and neutral and plasma temperatures.  相似文献   

Three–Dimensional Isotopic Characteristics of Crystalline Limestone around the Sakonishi Zn Ore Bodies in the Kamioka Mining District, Japan     

Yuichi MORISHITA 《Resource Geology》1999,49(4):243-257

Abstract: Predominant Zn-rich ore bodies were found to a deep part of the Sakonishi area in the Kamioka mining district, Japan. The ore mineralization was recognized at 230 to 300m above sea level in the Sakonishi area. Since crystalline limestone is broadly distributed over the area, and the variation in isotopic composition is easily detected, the isotopic prospecting should be powerful in surveying of the extent of the ore bodies and the related hydrothermal system. Although isotopic anomalies have been extracted two-dimensionally so far, three-dimensional information is possibly more powerful. In this paper, Zn-rich ore bodies in the Sakonishi area are treated as hydrothermal ore deposits, and the importance of the activity of hydrothermal fluids during mineralization is emphasized. Oxygen and carbon isotopic ‘iso–surfaces’ are three-dimensionally calculated for the Sakonishi area. The δ¹⁸O values of crystalline limestone from the surface and from the drill holes range from +8. 1 to +21. 1% and from –2. 7 to +20. 4%, respectively. The δ¹³C values of crystalline limestone from the surface and from the drill holes range from –1. 0 to +5. 3% and from –7. 7 to +4. 6%, respectively. The oxygen and carbon iso-topic ratios at the mineralization level are extremely low, but there are exceptions as to carbon isotopes. The oxygen isotopic ratios of crystalline limestone may decrease by isotopic exchange reaction with a hydrothermal fluid, while the carbon isotopic ratios slightly change. Since the precipitated calcite from a hydrothermal fluid has low carbon isotopic ratio and various oxygen isotopic ratio depending on the formation temperature, the bulk sample of crystalline limestone containing the precipitated calcite has oxygen and carbon isotopic ratios of relatively low values accordingly. Thus the decrease mechanism for carbon isotopic ratio of crystalline limestone is different from that for oxygen isotopic ratio. Samples with the carbon isotopic ratio of –4 to –8% are considered to be crystallized from hydrothermal fluids. Since the oxygen and carbon isotopic ratios of crystalline limestone at the ore mineralization level are low, the ore bodies are considered to have formed by a prominent hydrothermal activity. Thus oxygen and carbon isotopic ratios of crystalline limestone can be used as an indicator of the related hydrothermal activity. The alteration such as chloritization is intense near fractures in the Sakonishi area, showing that the hydrothermal system is controlled by a fracture system. It is assumed that the decreased isotopic ratios indicate the high degree of reactivity with hydrothermal fluids, and the depleted zone in oxygen and carbon isotopes may correspond to the conduit of the hydrothermal fluids.  相似文献