Jurassic accretion tectonics of Japan   总被引：40，自引：0，他引：40  

Yukio  Isozaki 《Island Arc》1997,6(1):25-51

Abstract The Jurassic accretionary complex and coeval granites in Japan represent remnants of the Jurassic arc-trench system developed between the Asian continent and Pacific Ocean. The Jurassic accretionary complex occurs as a large-scale nappe that is tectonically sandwiched between the overlying pre-Jurassic nappes and underlying post-Jurassic nappes. By virtue of new research styles (microfossil mapping and chronometric mapping) the following new views of the Jurassic accretionary complex in Japan, that suggest those for on-land exposed ancient accretionary complexes in general, have been obtained: (i) the accretion age of the Jurassic accretionary complex ranges over ～ 80 million years from the latest Triassic to earliest Cretaceous according to a reconstructed stratigraphy of component rocks (oceanic plate stratigraphy); (ii) the accretionary complex is subdivided into several nappe units, each characterized by unique oceanic plate stratigraphy; (iii) a tectonically downward-younging polarity is observed in the piled nappes; (iv) the Jurassic accretionary complex is composed of coherent-type and chaotic-type units, the former retaining the primary accretionary structures while the latter are characterized by collapsed and secondarily mixed materialslfabrics derived from the former; (v) the chaotic-type units predominate in volume over the coherent-type units; (vi) the accretionary complex suffered from a regional low-grade metamorphism (up to the lower greenschist facies) within ～10–20 million years after the accretion timing; and (vii) the lateral extent of the Jurassic accretionary complex in East Asia is intermittently traced from the Koryak mountains in Russia to North Palawan in the west Philippines for ～6000 km. Discussion focuses on (i) the low preservation ratio of the coherent-type units to the chaotic-type units with respect to frequent subduction erosion by seamount subduction; (ii) absence of the Franciscan-type melange, suggesting sedimentary mixing origin for the chaotic-type unit; (iii) a growth rate of the Jurassic accretionary complex compatible to modern analogues; and (iv) the total volume of the Jurassic accretionary complex in Japan with respect to the most likely terrigeiious elastics source along the 250 Ma continent-continent collision suture in central China (between the Sino-Korean and Yangtze blocks).  相似文献   

Damage to buildings and structures due to recent devastating wind hazards in East Asia   总被引：1，自引：0，他引：1  

Qingshan Yang  Rong Gao  Fan Bai  Tian Li  Yukio Tamura 《Natural Hazards》2018,92(3):1321-1353

Extreme wind events such as typhoons and tornadoes can cause devastating damage to structures and huge losses to human societies. This paper introduces recent devastating wind-related disasters in East Asia, including disasters in Japan, the Philippines and China, from 2013 to 2016. In particular, it describes several post-disaster investigations including those on Typhoon Haiyan in 2013 in the Philippines; typhoon Mujigae and two typhoon-associated tornadoes in October, 2015, in Guangdong, China; and a tornado in June, 2016 in Yancheng, China. Meteorological features, damage details and failure mechanisms of structures, factors related to damage generation and spread, scales to evaluate storms, estimations of tornado wind speeds and so on are discussed, with the aim of mitigating future wind-related disasters and to create safer and sustainable societies. Lessons derived from aerodynamic effects, cladding and component performances, debris impacts, building arrangements, fatigue effects, construction methods, etc. together with suggestions for wind-resistant design of buildings are given.  相似文献   

Role of metal-organic complexes in the marine environment: A comparison of the copper and ligand titration methods     

Katsumi Hirose  Yukio Sugimura 《Marine Chemistry》1985,16(3):239-247

The differences in quality of the conditional stability constants deduced from ligand titration and metal titration methods are theoretically examined. The ecological role of the metal-organic complexes in seawater was considered on the basis of the concept of the metal buffering capacity index which is calculated from the conditional stability constant and the organic ligand concentration. The results of theoretical examination of the effect of metal contamination on the uptake of metals by phytoplankton indicate that the ecological significance of metal-organic complexes is essentially in the metal-buffering action. This means that the activities of free metal ions are maintained at a native constant level against relatively small perturbations by the addition or uptake of metals in the marine environment.  相似文献   

Some properties of surf-beats     

Yukio Fujinawa 《Journal of Oceanography》1979,35(1):9-25

Long ocean waves with periods of several minutes (surf-beats) were observed at a marine observation tower. We have analysed time series data of an envelope of incident swell, long period current velocity and surface elevation fluctuations. Current velocity was measued by an electromagnetic flow meter. Surf-beats amplitudeH ^(l) is shown to be proportional to 3/2 power of incident swell amplitudeH ^(s), and decreases with increase of depthh in proportional toh ^–1/2 such thatH ^(l) H ^(s) (H ^(s)/h)^1/2. Frequency energy density functionP _LL (f) of surface elevation had two dominant peaks whose frequencies were highly stable through the entire observational period. Cross-spectral analysis suggested that those peaks correspond to traveling edge waves caused by the excess momentum and mass flux in the surf zone. The forced long ocean waves predicted byLonguet-Higgins andStewart (1964) was ditected. Phase-shift and wave height of the wave with respect to those of incident swell envelope are shown to be in remarkable agreement with the predictions. However the forced long wave is only a minor component in the total energy of surf-beats. Current fields are shown to be largely composed of non-surface modes.  相似文献   

Seasonality of the Kuroshio Transport Revealed in a Kuroshio Assimilation System   总被引：2，自引：2，他引：2  

Atsuhiko Isobe  Masafumi Kamachi  Yukio Masumoto  Hiroshi Uchida  Tsurane Kuragano 《Journal of Oceanography》2004,60(2):321-328

The seasonal variation of the Kuroshio transport south of Japan has been investigated using the results of an assimilation model. Annual and semiannual variations of the transport and dynamic depth anomaly are reconstructed by CEOF (complex orthogonal empirical function) analysis. In the basin west of the Izu-Ogasawara Ridge, the annual component of the variation propagates westward with the phase speed of the long Rossby wave associated with the first baroclinic mode. The variation also shows a similar tendency to that reproduced in a wind-driven, two-layer model with a ridge. This suggests that the annual variation revealed in the assimilation model is associated with the baroclinic first mode of motion excited above the Izu-Ogasawara Ridge. Furthermore, it is found that both the semiannual component and the annual component are important members determining the seasonal variation of the Kuroshio transport south of Japan. The semiannual component is revealed as a double gyre pattern in the basin west of the Izu-Ogasawara Ridge. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Sensitivity of the Interannual Kuroshio Transport Variation South of Japan to Wind Dataset in OGCM Calculation   总被引：1，自引：2，他引：1  

Hiroshi Yoshinari  Motoyoshi Ikeda  Kiyoshi Tanaka  Yukio Masumoto 《Journal of Oceanography》2004,60(2):341-350

Numerical experiments were carried out using OGCM (Ocean General Circulation Model), MOM2.2 (Modular Ocean Model Ver. 2.2), over realistic topography data, ETOPO5 (Earth Topography - 5 Minute), to investigate the interannual variability of the Kuroshio transport in 1960–2000 south of Japan; 1) the PN line located off the East China Sea, and 2) the ASUKA (Affiliated Surveys of the Kuroshio off Cape Ashizuri) line located off Cape Ashizuri. We adopted two wind datasets as driving forces of the OGCM: 1) the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis monthly mean wind stress data, and 2) the ECMWF (European Centre for Medium-range Weather Forecasts) daily wind data. In the ECMWF experiments we replaced the NCEP/NCAR data only in 1979–1993 because of the availability of the data. The OGCMs and observation basically agree on the temporal variation patterns of the transports until 1986 on the PN line with correlation coefficients of about 0.6. During the 1990s, when data were collected on the ASUKA line, the NCEP/NCAR experiments give lower correlation coefficients (less than 0.3), on both PN and ASUKA lines, while the ECMWF experiments have a higher value on the ASUKA line (0.5). One of the reasons for the disagreement between the observations and OGCMs during the 1990s might arise from the NCEP/NCAR data. An additional analysis of a wind-driven circulation was performed to examine the sensitivity of integrated Sverdrup transport along the western boundary to the propagation speed of a baroclinic Rossby wave, which is varied by stratification. A variation of the stratification, which might be induced by variability of air-sea heat and freshwater fluxes, cannot be a main cause of the disagreement. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Generation of Small Meanders of the Kuroshio South of Kyushu in a High-Resolution Ocean General Circulation Model     

Yukio Masumoto 《Journal of Oceanography》2004,60(2):313-320

The generation of small meanders of the Kuroshio south of Kyushu has been investigated using a high-resolution ocean general circulation model of the North Pacific Ocean. The small cyclonic meander develops in the region east of the Tokara Strait with a period of about one month, then propagates downstream along the Kuroshio path to the longitude of the Kii Peninsula, which is similar to the so-called trigger meanders for the formation of the large-meander of the Kuroshio south of Japan. It turns out that the generation of the small meander is a local phenomenon, strongly associated with anticyclonic eddies that propagate northeastward along the Kuroshio path in the East China Sea. The vorticity balance indicates that the accumulation of positive vorticity during the developing phase of the small meander occurs mainly from the balance between the stretching and the advection terms. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Thorium concentration and the activity ratios230Th/232Th and228Th/232Th in sea water in the western North Pacific     

Yasuo Miyake  Yukio Sugimura  Tadahide Yasujima 《Journal of Oceanography》1970,26(3):130-136

The concentration of thorium isotopes and the activity ratios of²³⁰Th/²³²Th and²²⁸Th/²³²Th in sea water collected in the Kuroshio region, the mixing area of Oyashio and Kuroshio, the Japan Sea and the East China Sea in the western North Pacific were determined. Thorium isotopes were analyzed by α-ray spectrometry after separating them with an anion exchange resin. The average content of thorium (²³²Th) of 2.2×10⁻⁹ g/l was obtained in the open Pacific waters. The ratio of²³⁰Th/²³²Th is in accord with that of the top layer of the sediment in the same area. The high values of²²⁸Th/²³²Th ratio up to 36 were observed in sea water. The excess²²⁸Th in sea water may be due to the migration of²²⁸Ra through the water-sediment interface. Thorium content in suspended matter was 10 to 20% of the total thorium content in the Pacific water.  相似文献   

New pop-up type Ocean Bottom Seismometer     

Takao Eguchi  Yukio Fujinawa  Tadayoshi Matsuzaki  Masaru Aoyagi 《Marine Geophysical Researches》1986,8(2):187-199

We designed a new pop-up type Ocean Bottom Seismometer (OBS) in order to study micro-earthquakes in off-shore areas. With a 57 cm O.D. sphere of high tension aluminium alloy, the OBS system, including one vertical and one horizontal geophone, can safely operate on ocean floors of up to 6000 m depth for seismic observations. The amplified seismic data and the time code are directly recorded on the four-channel cassette deck for periods of up to one month. The frequency response curve throughout the recording and play-back system is flat for the range, 1–15 Hz (–3 dB). The anchor release and the geophone clamp are operated by an acoustic command signal.So far, we have deployed our OBS's 42 times in the ocean. All of the OBS's deployed have been recovered safely. Seismic data has provided seismological evidence for a number of processes associated with tectonism along subduction zones and spreading ridges (e.g., Eguchi et al., 1986).  相似文献   

A numerical simulation of the distribution of water temperature and salinity in the Seto Inland Sea     

Mayumi Murakami  Yukio Oonishi  Hideaki Kunishi 《Journal of Oceanography》1985,41(4):213-224

Constant flows, as well as oscillatory tidal flow, play an important role in the long-term dispersion of water in the Seto Inland Sea. Two kinds of numerical model (1-line and 2-line models) of the Seto Inland Sea have been developed to determine the role of density-induced currents, one type of the constant flow, in water dispersion in the Inland Sea. The seasonal variations of temperature, salinity and density fields are simulated and the density-induced current field is predicted at the same time. It is found that the most appropriate value of the longitudinal eddy diffusion coefficient,K _x, is 5×10⁶–7×10⁶ cm²sec^–1. The value of the overall mean dispersion coefficient is of the order of 10⁷cm²sec^–1 (Hayami and Unoki, 1970). Consequently, it is suggested that 50–70% of the total dispersion in the Seto Inland Sea can be attributed to currents other than density-induced currents,i.e., tidal currents, tide-induced currents and wind-driven currents.In winter, both density and velocity fields, calculated using the 1-line model, satisfy the conditions for the existence of a coastal front in Kii Channel and in the eastern Iyo-nada.  相似文献