Field observations of meteotsunami locally called “abiki” in Urauchi Bay, Kami-Koshiki Island, Japan     

Toshiyuki Asano  Toru Yamashiro  Norihiro Nishimura 《Natural Hazards》2012,64(2):1685-1706

A seasonal scale field observation extending over a period of 82?days was conducted in Urauchi Bay on Kami-Koshiki Island, to record meteotsunami events, disastrous secondary oscillations locally known as ??abiki.?? The bay has an elongated T-shape topography with a narrow mouth opening westward to the East China Sea. The area has suffered the effects of meteotsunami causing flooding in residential area and damage to fishing fleets and facilities. A comprehensive observation system for sea level, ocean currents and barometric pressure was deployed to cover the regions within and offshore from Urauchi Bay and the open sea near the island of Mejima in the East China Sea. Vigorous meteotsunami events, where the total height exceeded 150?cm, were observed over five-day periods during the observation period. One or two hours prior to the arrival of meteotsunami events at Kami-Koshiki Island, abrupt 1?C2?hPa pressure changes were observed at the Mejima observation site. Pressure disturbances were found to travel eastward or northeastward. The propagation speed was found to nearly coincide with that of ocean long waves over the East China Sea, and as a result, resonant coupling should be anticipated. The incoming long waves were also amplified by geometric resonance with eigen oscillations inherent in the T-shape topography of Urauchi Bay.  相似文献   

Inflations prior to Vulcanian eruptions and gas bursts detected by tilt observations at Semeru Volcano,Indonesia     

Takeshi Nishimura  Masato Iguchi  Ryohei Kawaguchi  Surono  Muhamad Hendrasto  Umar Rosadi 《Bulletin of Volcanology》2012,74(4):903-911

We examine the basic characteristics of inflations at Semeru Volcano, Indonesia, to clarify the pressurization process prior to two different styles of explosive eruptions: Vulcanian eruptions and gas bursts. Analysis of data obtained from tilt meters installed close to the active crater allows clarification of the common features and the differences between the two styles of eruptions. To improve the signal-to-noise ratio and to determine the mean characteristics of the inflations, we stack tilt signals obtained from eruptions of different magnitudes and evaluate the maximum amplitude of the seismic signal associated with these eruptions. Vulcanian eruptions, which explosively release large amounts of ash, are preceded by accelerating inflation about 200–300 s before the eruption, which suggests volume expansion of the gas phase. In contrast, gas bursts, which rapidly effuse water steam accompanied by explosive sounds, follow non-accelerating changes of inflation starting 20 s before each emission. Tilt amplitudes increase with the magnitude of eruptions for both eruption styles. This suggests that the volume and/or pressure of magma or gas stored in the conduit before eruptions controls the magnitude of volcanic eruptions. These results further suggest that the magnitude of eruptions can be predicted from geodetic measurements of volcano inflation.  相似文献   

Experimental studies on debris flow with logs focusing on specific weight difference of log species     

Haruki WATABE  Takahiro ITOH  Kazuhiko KAITSUKA  Shigeki NISHIMURA 《山地科学学报》2013,10(2):315-325

There are many experimental approaches,field investigations and numerical calculations for movements of woods in a clear water and debris flow.However,kinematic conditions for accumulated logs and the interactions between a main flow and logs have not been fully evaluated.Mitigations for woods need taking into account the characteristics of tree species such as conifer and broad-leaf trees and of shapes such as root swells and crown.In the present study,we focus on the differences in specific weight of conifer and broad-leaf trees with some moisture in a sediment-water mixture flow with narrow flow width,and consider that conifer and broad-leaf tree are floating and submerged solid phase,respectively.Flume tests are conducted in steady flow of clear and debris flow over a rigid bed in order to evaluate conifer and broad-leaf tree movement in clear water and debris flow.Experimental data indicates that dimensionless transverse diffusion coefficient can be 0.1 to 0.4 and 0.3 to 0.9 in flow direction.Those diffusive characteristics seem to be independent of Reynolds number and Froude number,but dependent of bed slope,i.e.,gravity,though detailed considerations are needed to discuss about flow characteristics such as spatial eddy structures,momentum transfer induced by interactions of logs and so on.  相似文献   

Recursive formula for the peak delay time with travel distance in von Kármán type non-uniform random media on the basis of the Markov approximation     

Tsutomu Takahashi  Haruo Sato  Takeshi Nishimura 《Geophysical Journal International》2008,173(2):534-545

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Overview of NOPACCS (Northwest Pacific Carbon Cycle Study)     

Hiroyuki Tsubota  Joji Ishizaka  Akira Nishimura  Yutaka W. Watanabe 《Journal of Oceanography》1999,55(6):645-653

The Northwest Pacific Carbon Cycle Study (NOPACCS) was a program aimed at investigating the carbon cycle of the North Pacific Ocean, which can be thought of as a large reservoir of carbon dioxide. NOPACCS was also aimed at estimating the North Pacific's capacity as a carbon sink. Project design, scientific results, and data availability, and subsequent projects resulting from this project are also described in this review. Studies of the upper ocean processes focused on the latitudinal differences in the fugacity of carbon dioxide; and on the detail of plankton community structures. Intermediate water was studied in relation to the formation of North Pacific Intermediate Water and the amount of accumulated anthropogenic carbon. The sedimentation process, past carbon cycle and coral reefs were also studied during the project. A preliminary, overall view of the carbon cycle of the North Pacific was drawn from the results of the project and compared to global values.  相似文献   

Sea-floor methane blow-out and global firestorm at the K–T boundary     

M. D. Max  W. P. Dillon  C. Nishimura  B. G. Hurdle 《Geo-Marine Letters》1999,18(4):285-291

 A previously unsuspected source of fuel for the global firestorm recorded by soot in the Cretaceous–Tertiary impact layer may have resided in methane gas associated with gas hydrate in the end-Cretaceous seafloor. End-Cretaceous impact-generated shock and megawaves would have had the potential to initiate worldwide oceanic methane gas blow-outs from these deposits. The methane would likely have ignited and incompletely combusted. This large burst of methane would have been followed by longer-term methane release as a part of a positive thermal feedback in the disturbed ocean-atmosphere system. Received: 16 September 1998 / revision received: 11 January 1999  相似文献   

Variability of the metallic-line star 28 Andromedae     

Shiro Nishimura 《Astrophysics and Space Science》1969,3(1):77-79

The metallic-line A-type star 28 And was found to be variable both in brightness and radial velocity. The brightness in blue varies by 0^m.05, and the radial velocity by 5 km/sec with a period of 102 minutes. The minimum light occurs 0.12 P before the maximum radial velocity. The relation of 28 And to Scuti variables is briefly discussed.  相似文献   

The location and size of a solar hard X-ray burst on September 27, 1969     

T. Takakura  K. Ohki  N. Shibuya  M. Fujii  M. Matsuoka  S. Miyamoto  J. Nishimura  M. Oda  Y. Ogawara  S. Ota 《Solar physics》1971,16(2):454-464

The location and size of a solar impulsive hard X-ray burst have been determined in one dimension to a considerable precision with a balloon-borne X-ray modulation collimator. The center of the X-ray source is on the line passing through the center of a big H flare region of 3 arc min. The size of the X-ray source is remarkably smaller and may be one arc min or less.  相似文献   

Rapid subsidence of the Kikai Seamount inferred from drowned Pleistocene coral limestone: Implication for subduction of the Amami Plateau,northern Philippine Sea     

Tsutomu Nakazawa  Akira Nishimura  Yasufumi Iryu  Tsutomu Yamada  Hiroshi Shibasaki  Satoshi Shiokawa 《Marine Geology》2008,247(1-2):35-45

Carbonate rock cores drilled on the Kikai Seamount, northern Philippine Sea are examined for better understanding of tectonic history of the northern Philippine Sea. The Kikai Seamount, the summit of which is at 1960 m water depth, is an isolated high on the northwestern part of the Amami Plateau formed by subduction-related arc volcanism, and is situated close to the axis of the Ryukyu Trench in front of the Ryukyu Arc, SW Japan. The seamount is capped with shallow-water carbonates such as coral rudstone. Detailed examinations of lithology, larger foraminiferal assemblages, and Sr isotope composition reveal that the core material comprises Miocene carbonates unconformably overlain by Early Pleistocene carbonates. It indicates rapid subsidence of the Kikai Seamount since the Early Pleistocene. The most probable cause of rapid subsidence is collision and subduction of the Amami Plateau laden with the Kikai Seamount. The rapid subsidence may have started when the western corner of the plateau reached the Ryukyu Trench and began subduction beneath the Ryukyu Arc. The onset of the subsidence is likely to be controlled by a motion change in the Philippine Sea Plate. The latest change in subduction direction from north to northwestward into northwestward to west has been believed to have occurred at 1-2 Ma during latest Pliocene to Early Pleistocene time. The change of direction resulted in the shift from oblique into right-angle subduction of the plate beneath the Ryukyu Arc and also the onset of the collision and subduction of the Amami Plateau.  相似文献   

Data assimilation using the particle filter for identifying the elasto‐plastic material properties of geomaterials     

Akira Murakami  Takayuki Shuku  Shin‐ichi Nishimura  Kazunori Fujisawa  Kazuyuki Nakamura 《国际地质力学数值与分析法杂志》2013,37(11):1642-1669

A computational method, incorporating the finite element model (FEM) into data assimilation using the particle filter, is presented for identifying elasto‐plastic material properties based on sequential measurements under the known changing traction boundary conditions to overcome some difficulties in identifying the parameters for elasto‐plastic problems from which the existing inverse analysis strategies have suffered. A soil–water coupled problem, which uses the elasto‐plastic constitutive model, is dealt with as the geotechnical application. Measured data on the settlement and the pore pressure are obtained from a synthetic FEM computation as the forward problem under the known parameters to be identified for both the element tests and the ground behavior during the embankment construction sequence. Parameter identification for elasto‐plastic problems, such as soil behavior, should be made by considering the measurements of deformation and/or pore pressure step by step from the initial stage of construction and throughout the deformation history under the changing traction boundary conditions because of the embankment or the excavation because the ground behavior is highly dependent on the loading history. Thus, it appears that sequential data assimilation techniques, such as the particle filter, are the preferable tools that can provide estimates of the state variables, that is, deformation, pore pressure, and unknown parameters, for the constitutive model in geotechnical practice. The present paper discusses the priority of the particle filter in its application to initial/boundary value problems for elasto‐plastic materials and demonstrates a couple of numerical examples. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献