Measurements of carbon dioxide in the Seto Inland Sea of Japan     

Eiji Yamashita  Fukuichi Fujiwara  Xiaohu Liu  Eiji Ohtaki 《Journal of Oceanography》1993,49(5):559-569

The carbon dioxide in seawater (pCO₂) was measured in the Seto Inland Sea of Japan using newly developed equilibrator instrument designed to be free from the correction for addition or extraction of the carbon dioxide from carrier gas. The temperature dependence of pCO₂ was about 4.5%pCO₂/°C for a single seawater sample which was processed as free from biological activity and change in total carbon dioxide content during an experiment. The decrease in pCO₂ during daylight hours due to the photosynthetic fixation was about 30% of the daily mean of pCO₂ during warm months and about 15% during cold months. The effect of carbon dioxide exchange between air and seawater on pCO₂ was about 0.6 ppm in August and about 0.1 ppm in March. This is negligible small compared with the daily oscillation of carbon dioxide in seawater.  相似文献   

Intrusion of less saline shelf water into the Kuroshio subsurface layer in the East China Sea   总被引：7，自引：0，他引：7  

Atsuhiko?IsobeEmail author  Eiji?Fujiwara  Pil-Hun?Chang  Koichi?Sugimatsu  Manabu?Shimizu  Takeshi?Matsuno  Atsuyoshi?Manda 《Journal of Oceanography》2004,60(5):853-863

The possible origin and cause of the less saline shelf water detected in the Kuroshio subsurface layer around the shelf edge of the East China Sea are investigated using observational results obtained in May 1998–2001 in conjunction with a dataset archived by Japan Oceanographic Data Center and a numerical model. The observations show that subsurface intrusions of less saline water are always detected in May in layers above 24.5σθ isopycnal surface, and that salinity inversions (i.e., areas in which the less saline water lies beneath the saline water) are detected around the trough of the Kuroshio frontal eddy (or wave). Analyses of the archived dataset reveal that the isopycnal surface of 24.5σθ is the deepest layer of the Kuroshio pycnocline outcropping to the sea surface on the shallow shelf in early spring. Outcropping isopycnals above 24.5σθ encounter a less saline water plume originating from the Changjiang, especially in the western East China Sea. Thereafter, the less saline water moves along isopycnal layers and reaches the Kuroshio front around the shelf edge. Numerical models demonstrate that, when the frontal wave captures the less saline water, the shelf water takes the form of a salinity inversion in the trough because isohalines in the frontal wave have a phase lag between the upper and lower layers in consequence of the baroclinic instability.  相似文献   

A real-time observation network of ocean-bottom-seismometers deployed at the Sagami trough subduction zone,central Japan     

Eguchi  Takao  Fujinawa  Yukio  Fujita  Eisuke  Iwasaki  Sin-Iti  Watabe  Isao  Fujiwara  Hiroyuki 《Marine Geophysical Researches》1998,20(2):73-94

We installed a real-time operating regional observation network of Ocean-Bottom-Seismometers, connected to an electro-optical fiber communication cable, at the Sagami trough subduction zone, just south of the Tokyo metropolitan area, central Japan. The network, called ETMC, has six seismic observation sites at approximately 20 km spacing. In addition, there are three tsunami observation sites along the ETMC network to monitor the propagation process of tsunamis around the Sagami trough region.The on-line data from the ETMC has been improving the detection capability of smaller-magnitude earthquakes even at areas close to the margin of the trough. The ETMC data analyzing system, which has a function of real-time digital filtering for each seismic channel, can read the arrival times of P- and S-waves precisely, constraining well the automatic on-line hypocenter locations. The network has been providing useful information regarding the bending and downgoing process of the Philippine sea plate at the Sagami trough subduction zone.The pressure sensors of the installed network have a detection capability of tsunami wave trains with an amplitude of less than 1 cm. For example, the sensors recorded the full time history of tsunami wave trains, with mm order resolution, originating from a tsunami earthquake with 5.7 M_W and the tsunami magnitude of 7.5 occurred near Tori Shima (Tori Is.) of the Izu-Bonin Is. arc on September 4, 1996. The maximum amplitude of the tsunami signals on the trough-floor was approximately 1 cm (P-P), in contrast with approximately 20 cm (0-P) at a coastal site on Izu-Oshima, near the trough. Also, the pressure sensors observed tsunamis due to a large tsunami earthquake (7.1 M_W) at the northern New Guinea, on July 17, 1998.  相似文献   

Interpretation of landslide distribution triggered by the 2005 Northern Pakistan earthquake using SPOT 5 imagery   总被引：7，自引：4，他引：7  

Hiroshi P. Sato  Hiroyuki Hasegawa  Satoshi Fujiwara  Mikio Tobita  Mamoru Koarai  Hiroshi Une  Junko Iwahashi 《Landslides》2007,4(2):113-122

The 2005 northern Pakistan earthquake (magnitude 7.6) of 8 October 2005 occurred in the northwestern part of the Himalayas. We interpreted landslides triggered by the earthquake using black-and-white 2.5-m-resolution System Pour l’Observation de la Terre 5 (SPOT 5) stereo images. As a result, the counts of 2,424 landslides were identified in the study area of 55 by 51 km. About 79% or 1,925 of the landslides were small (less than 0.5 ha in area), whereas 207 of the landslides (about 9%) were large (1 ha and more in area). Judging from our field survey, most of the small landslides are shallow rock falls and slides. However, the resolution and whitish image in the photos prevented interpreting the movement type and geomorphologic features of the landslide sites in detail. It is known that this earthquake took place along preexisting active reverse faults. The landslide distribution was mapped and superimposed on the crustal deformation detected by the environmental satellite/synthetic aperture radar (SAR) data, active faults map, geological map, and shuttle radar topography mission data. The landslide distribution showed the following characteristics: (1) Most of the landslides occurred on the hanging-wall side of the Balakot–Garhi fault; (2) greater than one third of the landslides occurred within 1 km from the active fault; (3) the greatest number of landslides (1,147 counts), landslide density (3.2 counts/km²), and landslide area ratio (2.3 ha/km²) was found within Miocene sandstone and siltstone, Precambrian schist and quartzite, and Eocene and Paleocene limestone and shale, respectively; (4) there was a slight trend that large landslides occurred on vertically convex slopes rather than on concave slopes; furthermore, large landslides occurred on steeper (30° and more) slopes than on gentler slopes; (5) many large landslides occurred on slopes facing S and SW directions, which is consistent with SAR-detected horizontal dominant direction of crustal deformation on the hanging wall.  相似文献   

The evolution of Pinatubo aerosols in the Arctic stratosphere during 1994–2000     

Masaharu Watanabe  Yasunobu Iwasaka  Takashi Shibata  Masahiko Hayashi  Motowo Fujiwara  Roland Neuber   《Atmospheric Research》2004,69(3-4):199-215

Balloon-borne aerosol measurements were performed with an optical particle counter between 1994 and 2000 at Ny-Ålesund (79°N), Svarbard. Throughout the observation period, continuous decay was found in the concentrations of particles with 0.4–0.6 μm in radius in the Arctic stratosphere, suggesting that Pinatubo aerosols remained even at the end of the 1990s. The decay rate was clearly higher for larger particle sizes, and higher at higher altitude (e-folding time of 970–526 days), suggesting a gravitational sedimentation effect. For smaller particles with R<0.4 μm, slight increases in concentration with time were found, which agreed with the measurements at mid-latitude. The sulfate mass mixing ratio in the Arctic stratosphere before 1998 showed values higher than those at middle latitude, while values were almost the same in both regions after 1998. A possible explanation of the latitudinal difference is a time lag (of 0.5–1 year) in the arrival of Pinatubo aerosols in the Arctic.  相似文献   

Meteor Orbit Determinations with Multistatic Receivers Using the MU Radar     

Yasunori Fujiwara  Yoshiyuki Hamaguchi  Takuji Nakamura  Masaki Tsutsumi  Makoto Abo 《Earth, Moon, and Planets》2008,102(1-4):309-314

The MU radar of RISH (Research Institute for Sustainable Humanosphere, Kyoto University), which is a MST radar (46.5 MHz, 1 MW peak power), has been successfully applied to meteor studies by using its very high versatility. The system has recently renewed with 25 channel digital receivers which significantly improved the sensitivity and precision of interferometer used in meteor observation. The transmission is now synchronized to GPS signals, and two external receiving sites with a ranging capability has additionally been operated in order to determine the trajectories and speeds of meteoroids.  相似文献   

Imaging an asperity of the 2003 Tokachi-oki earthquake using a dense strong-motion seismograph network     

R. Honda  S. Aoi  H. Sekiguchi  H. Fujiwara 《Geophysical Journal International》2008,172(3):1104-1116

The 2003 Tokachi-oki earthquake ruptured a large area of approximately 100 km². The location of the largest asperity was estimated to be several dozen kilometres offshore of Hokkaido, Japan. The magnitude measured 8.0 on the Japan Meteorological Agency scale, and several studies used waveform inversion analysis to estimate the moment-magnitude as M _w 8.0–8.2. Several studies reported that there was a minor asperity at the northeastern edge of the fault plane, and that the rupture velocity towards the minor asperity was less than that towards the main asperity. One of them illustrated that the location and timing of the minor asperity were poorly constrained. In this paper, we introduce a procedure based on semblance analysis to image the location of the minor northeastern asperity with improved resolution. We group 15 strong-motion seismographs into three arrays, and we perform semblance analysis on impulsive waves that were possibly generated from the minor asperity and were conspicuously observed at stations in eastern Hokkaido. By projecting the semblance values onto the fault plane, we estimate the location of the minor asperity. We find it to be shallower and farther from the coast than the previous results indicated. The average rupture velocity towards the asperity is estimated to be 2.5 km s⁻¹, which is slower than the 3.6 km s⁻¹ obtained by waveform inversion analysis.  相似文献   

Compact Two-Dimensional Array of Stressed GE:GA Detectors     

Y. Doi  S. Makiuti  H. Okuda  T. Nakagawa  H. Shibai  M. Kawada  N. Hiromoto  M. Fujiwara  K. Okumura 《Experimental Astronomy》2000,10(2-3):393-401

We have developed a 4 × 8 array of stressed Ge:Ga detectors. This array detector has a high density format ofentrance pupils so that we can minimize the size of the cameraoptics. The cutoff wavelength of the detector is about 170 m, and the detector's NEP is better than 10¹⁶ WHz^-1/2. We are going apply this array detector toballoon-borne astronomical observations. Furthermore, we aredeveloping this detector into a 5 × 15 array detector that will be placed onboard the IRIS satellite to be launched in 2003.  相似文献   

Impact fracture patterns on phobos ellipsoids     

Akira Fujiwara  Noriaki Asada 《Icarus》1983,56(3):590-602

Phobos-ellipsoid models made of clay were fragmented by the impact of high-velocity projectiles to examine the idea proposed by P. Thomas, J. Veverka, and T. Duxbury ((1978) Nature273, 282–284) that the grooves on Phobos are the manifestation of fractures produced by the Stickney-forming impact. The fracture lines on the models consist of two sets. One is concentric around the impact site and along E lines, which are defined as the intersecting lines of the ellipsoid surface and a set of spherical surfaces with the center of the spheres at the impact site. The other runs radially from the impact site and along P lines, which are defined as the lines crossing E lines perpendicularly on the ellipsoid surface. Some patterns of the grooves originating radially from the crater Stickney on Phobos are very similar to the P lines. The gridded topography, hummocky groove sections, and smooth topography on Phobos could have been formed by the fracture or associated surface disturbances due to the wave induced by the Stickney-forming impact, because they are distributed along the E lines surrounding the converging point of the P lines. All the models except one showed that the density of the fractures east of the impact site is greater than that of those to the west. Fracture patterns similar to one of the most prominent groove sets, which converge and diminish into the region of about (270°, 0°) were not produced by the impact on the ellipsoid of uniform constituent. These grooves would have been produced by the opening of preexisting cracks by the Stickney-forming impact. Other grooves also seem to be affected by such latent cracks.  相似文献   

Correlation of the Hakkoda–Kokumoto Tephra, a widespread Middle Pleistocene tephra erupted from the Hakkoda Caldera, northeast Japan     

Takehiko  Suzuki  Dennis  Eden  Toru  Danhara  Osamu  Fujiwara 《Island Arc》2005,14(4):666-678

Abstract A Middle Pleistocene widespread tephra referred to here as Hakkoda–Kokumoto Tephra (Hkd–Ku) has been newly recognized. Hkd–Ku, derived from the Hakkoda Caldera located in northernmost Honshu Is. of northeast Japan, covers much of Honshu Is. At the type locality in the proximal area, Hkd–Ku comprises Plinian pumice deposits and an immediately overlying ignimbrite. The fine vitric ash nature of the distal ash‐fall deposits of Hkd–Ku suggests that they are coignimbrite ash‐fall deposits. Hkd–Ku was identified using a combination of refractive indices and chemical compositions of major, trace and rare earth elements of glass shards, heavy mineral content, refractive indices of orthopyroxene and paleomagnetic polarity. On the basis of these properties, Hkd–Ku was identified in Oga and Boso Peninsulas and Osaka Plain, 830 km southwest of the source. Stratigraphic positions in Boso Peninsula and Osaka Plain within marine sediments that have a reliable chronology based on oxygen‐isotope, and litho‐, bio‐, magneto‐ and tephrostratigraphy indicate that the age of Hkd–Ku is ca 760 ka, positioned in the transition between marine oxygen‐isotope stages 19.1 and 18.4. The widespread occurrence of Hkd–Ku providing a tie line between many different Pleistocene sections over a distance of 800 km is a key marker horizon in the early part of the Middle Pleistocene. This tephra gives a time control point of ca 760 ka to marine sediments in the Oga Peninsula – where no datum plane exists between the Brunhes–Matuyama chron boundary and oxygen‐isotope stage 12 – and to the volcanostratigraphy of the Hakkoda Caldera. The distribution of Hkd–Ku showing emplacement of coignimbrite ash‐fall deposits in the area 830 km southwest of the source emphasizes the upwind transport direction, relative to the prevailing westerly winds, typical of other coignimbrite ash‐fall deposits in the Japanese islands.  相似文献