Transition from frontal accretion to underplating in a part of the Nankai Trough Accretionary Complex off Shikoku (SW Japan) and extensional features on the lower trench slope     

Jeremy Leggett  Yutaka Aoki  Takefumi Toba 《Marine and Petroleum Geology》1985,2(2):131-141

Migrated multichannel seismic reflection profiles and bathymetry from a 200 × 120 km area of the Nankai Trough inner slope reveal three physiographic-tectonic domains on the lowermost slope. Linear ridges demarking laterally-continuous hangingwall anticlines above ramps in a relatively simple imbricate stack of trench turbidites characterize the western domain. An imbricate fan underlies a relatively flat structural terrace in the east. Between these two domains lies a compound knoll (Minami Muroto Knoll) some 40 km long, opposite which the thrust front pushes some 10 km further seaward than is the case in the domains to east and west. In the western ‘linear-ridge’ domain previous DSDP drilling penetrated turbiditic trench fill uplifted in the lowermost thrust-fold terrace above a decollement within the underthrusting Shikoku Basin (oceanic plate) sequence. The Shikoku Basin sequence in the western domain is divided into an upper, poorly reflective, hemipelagic claystone unit and a lower, strongly reflective, unit comprising Pliocene turbidites. The lower unit is traceable intact up to c.20 km landward below the lower trench slope and in the better resolved profiles the decollement lies along the base of the claystone unit. A similar decollement within the Shikoku Basin sequence in the eastern domain is traceable up to c.22 km landward. A critical seismic record crossing the western part of Minami-Muroto Knoll shows that the decollement is traceable only 8 km landward to a point, under the steep slope at the front of the knoll, landward of which the subducting Shikoku basin sequence is apparently thickened by as much as twice. This thickening, occuring as it does immediately along-strike from a simple imbricate fan to the east of the knoll and a relatively simple imbricate stack to the west (both evidently involving no strata from the lower Shikoku Basin unit) we ascribe to underplating by formation of duplexes of Shikoku Basin strata. Strike-parallel extension, akin to that postulated for high structural levels in certain thrust belts, is caused by uplift of the knoll as a result either of the underplating, or segmentation of the subducting oceanic crust, or both: a normal fault throws to the west off the west flank of the knoll. It bounds a transverse, trough-like, slope-basin with at least 900 m of fill. Upslope from the knoll broadly slope-parallel normal faults cut, and pond, recent slope sediments. The most impressive is a listric growth fault which dips trenchward. Alternative explanations for these involve extensional collapse of this part of the prism resulting from the subduction of a topographic high, or a zone of selective underplating below the trenchward portion of Minami Murato Knoll.  相似文献   

A quantitative study of seismic anisotropy in the Yamato Basin, the southeastern Japan Sea, from refraction data collected by an ocean bottom seismographic array     

Tae Woong Chung 《Geophysical Journal International》1992,109(3):620-638

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Evaluating the impacts of fine-scale capillary heterogeneity and wettability on the behavior of buoyancy-driven CO<Subscript>2</Subscript> migration and trapping mechanisms     

Sung Soo Park  Tae Hong Kim  Moon Sik Jeong  Kun Sang Lee 《Environmental Earth Sciences》2016,75(7):550

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Boldness in a deep sea hermit crab to simulated tactile predator attacks is unaffected by ocean acidification     

Tae Won Kim  James P. Barry 《Ocean Science Journal》2016,51(3):381-386

Despite rapidly growing interest in the effects of ocean acidification on marine animals, the ability of deep-sea animals to acclimate or adapt to reduced pH conditions has received little attention. Deep-sea species are generally thought to be less tolerant of environmental variation than shallow-living species because they inhabit relatively stable conditions for nearly all environmental parameters. To explore whether deep-sea hermit crabs (Pagurus tanneri) can acclimate to ocean acidification over several weeks, we compared behavioral “boldness,” measured as time taken to re-emerge from shells after a simulated predatory attack by a toy octopus, under ambient (pH ～7.6) and expected future (pH ～7.1) conditions. The boldness measure for crab behavioral responses did not differ between different pH treatments, suggesting that future deep-sea acidification would not influence anti-predatory behavior. However, we did not examine the effects of olfactory cues released by predators that may affect hermit crab behavior and could be influenced by changes in the ocean carbonate system driven by increasing CO₂ levels.  相似文献   

Adjustment of Wind Waves to Sudden Changes of Wind Speed   总被引：1，自引：0，他引：1  

Takuji Waseda  Yoshiaki Toba  Marshall P. Tulin 《Journal of Oceanography》2001,57(5):519-533

An experiment was conducted in a small wind-wave facility at the Ocean Engineering Laboratory, California, to address the following question: when the wind speed changes rapidly, how quickly and in what manner do the short wind waves respond? To answer this question we have produced a very rapid change in wind speed between U _low (4.6 m s^?1) and U _high (7.1 m s^?1). Water surface elevation and air turbulence were monitored up to a fetch of 5.5 m. The cycle of increasing and decreasing wind speed was repeated 20 times to assure statistical accuracy in the measurement by taking an ensemble mean. In this way, we were able to study in detail the processes by which the young laboratory wind waves adjust to wind speed perturbations. We found that the wind-wave response occurs over two time scales determined by local equilibrium adjustment and fetch adjustment, Δt ₁/T = O(10) and Δt ₂/T = O(100), respectively, in the current tank. The steady state is characterized by a constant non-dimensional wave height (H/gT ² or equivalently, the wave steepness for linear gravity waves) depending on wind speed. This equilibrium state was found in our non-steady experiments to apply at all fetches, even during the long transition to steady state, but only after a short initial relaxation Δt ₁/T of O(10) following a sudden change in wind speed. The complete transition to the new steady state takes much longer, Δt ₂/T of O(100) at the largest fetch, during which time energy propagates over the entire fetch along the rays (dx/dt = c _g) and grows under the influence of wind pumping. At the same time, frequency downshifts. Although the current study is limited in scale variations, we believe that the suggestion that the two adjustment time scales are related to local equilibrium adjustment and fetch adjustment is also applicable to the ocean.  相似文献   

The steepness and shape of wind waves     

Richard J. Bailey  Ian S. F. Jones  Yoshiaki Toba 《Journal of Oceanography》1991,47(6):249-264

Variations are found in the shape and the steepness of wind-generated surface gravity waves between very young waves, such as seen in a laboratory tank, and larger waves of various wave ages encountered at sea as the result of wind stress over larger fetches. These differences in the characteristic shape of wind waves are presented as a function of the wave age. The wave steepness is also expressed as a function of wave age, the measurement of which is consistent with the 3/2-power law connecting wave height and characteristic period, normalized by the air friction velocity.  相似文献   

Statistical study on the local equilibrium between wind and wind waves by using data from ocean data buoy stations   总被引：6，自引：0，他引：6  

Naoto Ebuchi  Yoshiaki Toba  Hiroshi Kawamura 《Journal of Oceanography》1992,48(1):77-92

The local equilibrium between the wind and wind waves, which is defined by a range of the coefficient of the 3/2-power law between the non-dimensional significant wave height and period, is statistically investigated by using wind and wave data obtained at four ocean data buoy stations in the seas near Japan. The friction velocity is calculated from the wind speed measured at one height together with the significant wave period by using formulas of the wave dependent drag coefficient proposed by Tobaet al. (1990). The data for small waves or for weak winds indicate that the waves do not satisfy the criterion for the local equilibrium, because they may be affected by changing winds or remotely generated swells. In the seas near Japan, the data which satisfy the local equilibrium are about 6% through a year. Otherwise swells are dominant in most situations. Changing winds also cause deviations from the local equilibrium. The degree of satisfaction of the local equilibrium can be classified by ranges of the significant wave height. As the significant wave height exceeds 4 m, the local equilibrium is more frequently satisfied.  相似文献   

Heat balance of the surface layer of the sea at ocean weather station T     

Yoshikazu Kurasawa  Kimio Hanawa  Yoshiaki Toba 《Journal of Oceanography》1983,39(4):192-202

Heat balance of the upper 200 m of the sea south of Japan is studied, by the use of marine meteorological and oceanographic data at Ocean Weather Station T (29°N, 135°E), intensively obtained from June 1950 to November 1953. Local time change of the heat content in the surface layer and the net heat flux through the air-sea interface are calculated directly from these data, and the heat convergence in the sea is estimated from their residuals. Regarding the relative importance of one- and three-dimensional processes, it is found that, on a time scale of a few days to one month, the variation of heat content depends on heat convergence in the sea, while on a seasonal time scale, the heat content is determined primarily by the heat flux through the sea surface in December through February, by heat convergence within the sea from March to May, and by both processes from June to November. It is inferred that the heat convergence in the sea is caused by advection of water masses which are bounded by sharp fronts. Spectral analysis of sea surface temperature indicates that they typically take 2 to 3 days to pass the station, and their typical size is estimated as around 20 km by assuming the typical advection velocity of water masses to be 10 cm s^?1.  相似文献   

Local balance in the air-sea boundary processes     

Yoshiaki Toba 《Journal of Oceanography》1972,28(3):109-120

A new growth equation for wind waves of simple spectrum is presented upon three basic concepts. The period and the wave height of significant waves in dimensionless forms, which are considered to correspond to the peak frequency and the energy level, respectively, are used as representative quantities of wind waves. One of the three basic concepts is the concept of local balance, and the other two concern the acquisition of wave energy and the dissipation of wave energy, respectively. It is shown from some actual data that the equation, together with two universal constants concerning the acquisition and the dissipation of wave energy (B=6.2×10^?2 andK=2.16×10^?5, respectively), is applied universally to wide ranges of wind waves from those in a wind-wave tunnel to fully developed sea in the open ocean. “The three-second power law for wind waves of simple spectrum”, and a few relations as the lemmas, are derived, such that the mean surface transport due to the orbital motion of wind waves is always proportional to the friction velocity in wind, and that the steepness is inversely proportional to the root of the wave age. It is also derived that the portion of wind stress which directly enters the wind waves decreases exponentially with increasing wave age and is 7.5 % of the total wind stress for very young waves. Also, equations are presented as to the increase of momentum of drift current, and as to the supply of turbulent energy by wind waves into the upper ocean.  相似文献   

Studies on physical processes at the sea surface     

Yoshiaki Toba 《Journal of Oceanography》1989,45(5):350-359

I feel greatly honoured to be awarded the Oceanographical Society of Japan Prize for 1989, and to be given this opportunity to look back at my past activities in research and education, and to present them as an example for younger members of our Society. Taking this opportunity, I acknowledge with sincere thanks many persons who guided me or who have collaborated with me since I was a young student up to the present.My past academic history may be divided into three periods. In the first period (1955–71) at Kyoto University which included and eighteen month visit to the University of Chicago, I studied the production of air bubbles and droplets at the sea surface by wind-wave breaking, and the supply and distribution of the sea-salt particles from the sea to the atmosphere. The first nondimensional formulation of the form of single air bubbles floating at liquid surfaces was also presented. In the second period (1971–1981) I pursued, at the new Physical Oceanography Laboratory of Tohoku University, the concept of wind waves which are coupled with the wind. I proposed the 3/2-power law of wind waves and the high frequency part of the wind-wave spectral form which is proportional to the friction velocity of air and to the –4th power of frequency. Detailed investigations of wind-wave phenomena were also performed in wind-wave tunnels by introducing quantitative flow visualization techniques and together with my students, we elucidated ordered motions in the flows below and above wind waves. The Tohoku Wave Model was also developed in which the similarity laws of wind waves, which are strongly coupled with the air flow, were explicitly used. In the third period (1982-present), my area of interest has become broader and, togerther with my students and my overseas collaboratos, we are studying the connection of local physical processes at the air-sea boundary with studies of larger scale ocean-atmosphere interactions. One aspect of this has led to the organization of the Ocean Mixed Layer Experiment (OMLET, 1987–91), as part of the Japanese national programmes of the World Climate Research Programme. Another interest is the ongoing fundamental study of the use of satellite data for the estimation of air-sea fluxes over a broad area. Pursuit of the roots of the similarity laws of the windsea remains one of my present tasks.  相似文献