Feeding of copepods on natural suspended particles in Tokyo Bay     

Atsushi Tsuda  Takahisa Nemoto 《Journal of Oceanography》1988,44(5):217-227

Community grazing rates of copepods were estimated from data taken during three cruises in Tokyo Bay, based on bottle incubations and a temporal variation of gut fluorescence. Special attention was paid to the feeding selectivity in the estimations. Differential grazing was observed in the copepod communities:Acartia omorii, abundant in February, selectively fed on the particles of dominant size classes, whileOithona davisae, dominant throughout the year, andCentropages abdominalis selected large particles (>20µm). The maximum filtering rates on certain size classes were several times the average. In addition, a 34-hr investigation of the gut fluorescence of copepods revealed nocturnal feeding inParacalanus spp.,Pseudodiaptomus marinus andOithona davisae.Copepod communities collected with a net (95-µm mesh opening) were estimated to graze, in February 3.0%, in August 3.1–4.5% and in November 4.2–11.9% of the standing crops of phytoplankton or suspended particles per day.  相似文献   

Monitored and simulated variations in matric suction during rainfall in a residual soil slope   总被引：1，自引：0，他引：1  

Aurelian C. Trandafir  Roy C. Sidle  Takashi Gomi  Toshitaka Kamai 《Environmental Geology》2008,55(5):951-961

This research combines field, laboratory and numerical investigations to estimate the development of a wetting front within a 1.2 m residual soil mantle on a steep forested slope during rainfall events. The field-monitored variations in matric suction due to rain-water infiltration during various events revealed that the maximum infiltration rate was much higher when the wetting front resided in the upper 20 cm of soil compared to the case when the wetting front advanced to depths > 20 cm. Laboratory investigations on soil hydraulic properties (i.e., soil water characteristic curve, and hydraulic conductivity) were useful to establish the parameters of a multilayer finite-element model for one-dimensional vertical infiltration. These parameters were subsequently calibrated by matching the predicted and field measured transient pore water pressure responses during actual rainstorms with irregular rainfall patterns. The calibrated simulation model was used to assess the migration of the wetting front under uniform rainfall with different intensities. Based on the numerical results, a hyperbolic equation was developed to predict the duration of uniform rainfall required for the propagation of wetting front to a certain depth for a given rainfall intensity. The proposed equation was subsequently tested against field-monitored advancements of the wetting front during real rainstorms with variable rainfall intensity.  相似文献   

Preface     

Atsushi Tsuda  Kazuhiro Kogure  Shuichi Watanabe 《Journal of Oceanography》2016,72(1):1-2

  相似文献   

A method for estimating casualties due to the tsunami inundation flow     

Shunichi Koshimura  Toshitaka Katada  Harold O. Mofjeld  Yoshiaki Kawata 《Natural Hazards》2006,39(2):265-274

This study develops a method for estimating the number of casualties that may occur while people evacuate from an inundation zone when a tsunami has inundated an area. The method is based on a simple model of hydrodynamic forces as they affect the human body. The method uses a Tsunami casualty index (TCI) computed at each grid point of a numerical tsunami model to determine locations and times within the tsunami inundation zone where evacuation during the tsunami inundation is not possible and therefore where casualties are likely to occur. The locations and times can be combined with information about population density to compute the potential number of casualties. This information is useful in developing tsunami evacuation routes that avoid such locations. To illustrate the method, it is applied to the Seattle waterfront in Washington State, USA, that is under the threat of possible tsunami disasters due to Seattle Fault earthquakes. Preliminary results suggest that the tsunami casualties may occur within the Seattle waterfront for 15 min, during the time interval from 3 to 18 min after a large Seattle Fault tsunami is generated when the background tide level is mean high water.  相似文献   

New discoveries in dynamics of an M8 earthquake-phenomena and their implications from the 2003 Tokachi-oki earthquake using a long term monitoring cabled observatory   总被引：1，自引：0，他引：1  

Hitoshi Mikada  Kyohiko Mitsuzawa  Hiroyuki Matsumoto  Tomoki Watanabe  Shigehiko Morita  Riyo Otsuka  Hiroko Sugioka  Toshitaka Baba  Eiichiro Araki  Kiyoshi Suyehiro 《Tectonophysics》2006,426(1-2):95

At the 2003 Tokachi-oki earthquake of M8, seafloor phenomena such as a generation process of tsunami, seafloor uplifts, turbidity current, etc., were observed using a cabled observatory installed on the seafloor. The turbidity current was observed as a benthic storm caused presumably by the mainshock. The seafloor uplifts were observed at the mainshock and continuously after the mainshock. The uplifts were 0.35, 0.37, and 0.12 m for epicentral distances of 25.5, 31.4, and 81.7 km, respectively. After the mainshock, a continuous uplift of the seafloor is observed at all three pressure gauge locations indicating that there was a change in the state of friction on the plate boundary interface by the mainshock. In this paper, we first show what was observed using the cabled observatory installed right above the focal area of the earthquake, and then we discuss to summarize these phenomena associated with the earthquake, its possible causes, and future directions in long term monitoring of seismogenic processes.  相似文献   

On the initiation and movement mechanisms of a catastrophic landslide triggered by the 2008 Wenchuan (M<Subscript>s</Subscript> 8.0) earthquake in the epicenter area     

Shenghua Cui  Gonghui Wang  Xiangjun Pei  Runqiu Huang  Toshitaka Kamai 《Landslides》2017,14(3):805-819

The Niumiangou landslide (~7.5 × 10⁶ m³) was the largest that occurred in the town of Yingxiu (the epicentral area) during the 2008 Wenchuan earthquake. This landslide originated on a steep slope (~30°) that was located directly above the rupture surface of the responsible fault and then traveled ~2 km after flowing down the axes of two gently sloping (<12°) valleys. Evidence at the site indicates that the landslide materials were highly fluidized and underwent rapid movement. To examine the initiation and movement mechanisms of this landslide, we performed a detailed field survey, conducted laboratory tests on samples taken from the field, and analyzed the seismic motion. We conclude that the landside materials were displaced due to seismic loading during the earthquake and that liquefaction may have been triggered in saturated layers above the sliding surface with progressive downslope sliding, which resulted in the high mobility of the displaced materials. The liquefaction of colluvial deposits along the travel path due to loading by the sliding mass enhanced the mobility of the displaced mass originating in the source area. Using an energy-based approach, we estimated the dissipated energy in our cyclic loading test and the possible energy dissipated to the soil layer on the slope by the earthquake. We infer that the seismic energy available for the initiation of the slope failure in the source area may have greatly exceeded the amount required for the initiation of the liquefaction failure. The slope instability might have been triggered several seconds after the arrival of seismic motion.  相似文献   

Validation and Joint Inversion of Teleseismic Waveforms for Earthquake Source Models Using Deep Ocean Bottom Pressure Records: A Case Study of the 2006 Kuril Megathrust Earthquake     

Toshitaka Baba  Phil R. Cummins  Hong Kie Thio  Hiroaki Tsushima 《Pure and Applied Geophysics》2009,166(1-2):55-76

The importance of accurate tsunami simulation has increased since the 2004 Sumatra-Andaman earthquake and the Indian Ocean tsunami that followed it, because it is an important tool for inundation mapping and, potentially, tsunami warning. An important source of uncertainty in tsunami simulations is the source model, which is often estimated from some combination of seismic, geodetic or geological data. A magnitude 8.3 earthquake that occurred in the Kuril subduction zone on 15 November, 2006 resulted in the first teletsunami to be widely recorded by bottom pressure recorders deployed in the northern Pacific Ocean. Because these recordings were unaffected by shallow complicated bathymetry near the coast, this provides a unique opportunity to investigate whether seismic rupture models can be inferred from teleseismic waves with sufficient accuracy to be used to forecast teletsunami. In this study, we estimated the rupture model of the 2006 Kuril earthquake by inverting the teleseimic waves and used that to model the tsunami source. The tsunami propagation was then calculated by solving the linear long-wave equations. We found that the simulated 2006 Kuril tsunami compared very well to the ocean bottom recordings when simultaneously using P and long-period surface waves in the earthquake source process inversion.  相似文献   

Earthquake-induced displacements of gravity retaining walls and anchor-reinforced slopes     

Aurelian C. Trandafir  Toshitaka Kamai  Roy C. Sidle 《Soil Dynamics and Earthquake Engineering》2009

This paper examines in terms of seismic performance, the effectiveness of anchor reinforcement against gravity retaining walls used to stabilize a dry homogenous fill slope in earthquake-prone environment. Both analyzed stabilizing measures have the same design yield acceleration estimated from a limit equilibrium approach. The earthquake-induced displacements are calculated using a sliding block formulation of the equation of motion. Sliding failure along the base of the gravity retaining wall and rotational failure of the soil active wedge behind the wall, as well as rotational failure of the slide mass of the anchor-reinforced slope were considered in the present formulation. For the specific characteristics of the analyzed fill slope and input horizontal ground motion, the slope reinforced with anchors appears to experience vertical and horizontal seismic displacements at slope crest smaller by 12% and respectively, 32% than the vertical and horizontal earthquake-induced deformations estimated at the top of the active wedge behind the gravity retaining wall.  相似文献   

Mesozooplankton in the eastern and western subarctic Pacific: community structure, seasonal life histories, and interannual variability     

D. L. Mackas  A. Tsuda 《Progress in Oceanography》1999,43(2-4)

The zooplankton community of the subarctic Pacific is relatively simple, and contains a similar set of major species in all deep water areas of the subarctic Pacific. Their role in the food web varies considerably between coastal and offshore locations. In the oceanic gyres, microzooplankton and other mesozooplankton taxa replace phytoplankton as the primary food source for the dominant mesozooplankton species. Micronekton and larger zooplankton probably replace pelagic fish as major direct predators. Productivity and upper ocean biomass concentrations are intensely seasonal, in part because of seasonality of the physical environment and food supply, but also because of life history patterns involving seasonal vertical migrations (400–2000 m range) and winter dormancy. During the spring–summer season of upper ocean growth, small scale horizontal and vertical patchiness is intense. This can create local zones of high prey availability for predators such as planktivorous fish, birds, and marine mammals. On average, the cores of the subarctic gyres have lower biomass and productivity than the margins of the gyres. There is also some evidence that the Western Gyre is more productive than the Alaska Gyre, but more research is needed to confirm whether this east–west gradient is permanent. There is increasing evidence that the pattern of zooplankton productivity is changing over time, probably in response to interdecadal ocean climate variability. These changes include 2–3 fold shifts in total biomass, 30–60 day shifts in seasonal timing, and 10–25% changes in average body length.  相似文献   

Spatial variability of chemical tracers in surface snow along the traverse route from the coast to 1000 km inland at east Dronning Maud Land, Antarctica   总被引：1，自引：0，他引：1  

Toshitaka Suzuki  Yoshinori Iizuka  Teruo Furukawa  Kenichi Matsuoka  Kokichi Kamiyama  Okitsugu Watanabe 《极地研究(英文版)》2003,14(1)

1　IntroductionAntarcticicesheetisaburialgroundforatmosphericdeposition .Sincethereiscon tinuousinteractionbetweentheicesheetandtheatmosphere,variousatmosphericsub stancesareinjectedtotheicesheetsequentiallyintimeandspace.Therefore,verticalanalysesoftheicesheetprovideuswithinformationaboutpastclimaticchange (Delmas1 992 ;LegrandandMayewski 1 997)andhorizontalanalysesoftheicesheetprovideuswithknowledgeregardinglong rangetransportofairbornematerials (Kamiyamaetal.1 989;KreutzandMayewski 1 999)…  相似文献