The three-dimensional shear wave structure in the mantle by overtone waveform inversion - I. Radial seismogram inversion     

Toshiro Tanimoto 《Geophysical Journal International》1987,89(2):713-740

Summary. The three-dimensional (3-D) shear wave structure of the mantle, down to the depth of about 900 km, is obtained by inverting waveforms of radial component seismograms. Radial component seismograms contain large amplitude overtone signals which circle the Earth as wave packets and are sometimes called X1, X2, X3, … We use data which contain R1, X1 and X2 and filtered between 2 and 10mHz. It is shown that, unless each seismogram is weighted, all seismograms are not fitted uniformly. Only data from large earthquakes are fitted and the final velocity anomalies are biased by the small number of large earthquake data. Resolution is good at shallow depths, becomes worse in the intermediate depth range between about 400 and 500 km and then becomes better at greater depth ranges (600–900km). Even though we use only spheroidal mode data, velocity anomalies in the shallow structure show excellent correlation with the age of the surface rocks of the Earth. In the deeper regions, between about 600 and 900km, South America shows a fast velocity anomaly which may indicate the slab penetration beyond 700 km there. Another region which shows a fast velocity anomaly is the Mariana trench, but other subduction regions do not show such features.  相似文献   

The 3-D shear wave structure in the mantle by overtone waveform inversion-II. Inversion of X-waves, R-waves and G-waves   总被引：1，自引：1，他引：0  

Toshiro Tanimoto 《Geophysical Journal International》1988,93(2):321-334

  相似文献   

Reply     

Toshiro Tanimoto 《Geophysical Journal International》2004,159(1):369-369

  相似文献   

Tectonic signatures in coseismic gravitational energy change   总被引：3，自引：0，他引：3  

Toshiro Tanimoto  Taro Okamoto  Fabia Terra 《Geophysical Journal International》2002,149(2):490-498

  相似文献   

State of stress within a bending spherical shell and its implications for subducting lithosphere     

Toshiro Tanimoto 《Geophysical Journal International》1998,134(1):199-206

The state of stress within a bending spherical shell has some special features that are caused by sphericity. While most lithospheres are more like spherical shells than flat plates, our ideas of the state of stress have been dominated by flat-plate models. As a consequence, we might be missing some important aspects of the state of stress within subducting lithospheres. In order to examine this problem, we analyse spherical-shell bending problems from basic equations. We present two approaches to solve spherical-shell bending problems: one by the variational approach, which is suitable for global-scale problems, and the other by the asymptotic equation, which is valid to first order in h/R , where h is the thickness of the lithosphere and R is its curvature radius (i.e. under the assumption of small curvature). The form of the equation for displacement shows that wavelengths of deformation are determined by the spherical (elastic) effect and the gravitational buoyancy effect, for which only the latter effect is included in the usual flat-plate formulations. In the case of the Earth, the buoyancy force is dominant and, consequently, spherical effects are suppressed to a large extent; this explains why flat-plate models have been successful for Earth's lithospheric problems. On the other hand, the state of stress shows interesting spherical effects: while bending (fibre) stress along the subduction zone is always important, bending stress along the trench-strike direction can also be important, in particular when the subduction zone arc is small. Numerical results also indicate that compressive normal stress along the trench-strike direction is important when a subduction zone arc is large. These two stresses, the bending stress and the compressive normal stress, both along the trench-strike direction, may have important implications for intraplate earthquakes at subduction zones.  相似文献   

Brightness distribution of diffuse soft X-rays     

H. Iwanami  H. Kunieda  F. Nagase  K. Yamashita  T. Murakami 《Astrophysics and Space Science》1979,61(1):217-227

The brightness distribution of diffuse soft X-rays in the pulse height range 0.15–0.3 keV (L-band) and 0.5–0.8 keV (M-band) are obtained over a quarter of the sky centered at the galactic anticenter with 1.5 m polypropylene window proportional counters on board a sounding rocket. In theL-band three enhanced regions are noticed on the map. They coincide with the northern and southern Hi holes and the inner part of the galactic radio Loop II.In the northern Hi hole theN _H dependence of theL-band flux and the hardness ratioM/L can be fitted with a local hot plasma model with the absorption by a low velocity neutral hydrogen gas (|V|<25 km s^–1) along the line of sight. The X-ray feature of Loop II is similar to that of Loop I. In the lowN _H region (<3×10²⁰ H atoms cm^–2) theM/L value is lower than 0.3, whereas it varies in the range 0.1–0.4 at low latitudes (|b|<30⁰). This fact seems to be interpreted in terms of a model that a number of hot plasma clouds contribute to X-ray emission.  相似文献   

Transport mechanism of suspended matter above the shelf slope at the mouth of Tokyo Bay     

Tetsuo Yanagi  Takahide Hagita  Toshiro Saino  Takashi Ishimaru  Sinchiro Noriki 《Journal of Oceanography》1995,51(4):459-470

Transport mechanism of suspended matter above the shelf slope is investigated with the use of the moorings of time-series sediment trap, current meter and nephelometer at three stations at the mouth of Tokyo Bay, Japan during 21 to 25 August 1993. Tidal pump mechanism is effective for the transport of suspended matter at the shelf edge, but the boring-like flood tidal current resuspends the settled suspended matter, on the bottom of shelf slope and the resuspended matter is resulted to be moved upslope in one tidal cycle at 10 m above the bottom of shelf slope.  相似文献   

Three-year investigations into sperm whale-fall ecosystems in Japan   总被引：2，自引：0，他引：2  

Yoshihiro Fujiwara  Masaru Kawato  Tomoko Yamamoto  Toshiro Yamanaka  Waka Sato-Okoshi  Chikayo Noda  Shinji Tsuchida  Tomoyuki Komai  Sherine Sonia Cubelio  Takenori Sasaki  Karen Jacobsen  Kaoru Kubokawa  Katsunori Fujikura  Tadashi Maruyama  Yasuo Furushima  Kenji Okoshi  Hiroshi Miyake  Masayuki Miyazaki  Yuichi Nogi  Akiko Yatabe  & Takashi Okutani 《Marine Ecology》2007,28(1):219-232

We report the first study of sperm whale‐fall ecosystems, based on mass sinking of whale carcasses at shelf depths in the northwest Pacific. We conducted three observations over a 2‐year period on replicate sperm‐whale carcasses implanted at depths of 219–254 m off the southern part of Japan from July 2003 to August 2005. The study was made possible by a mass stranding of sperm whales in January 2002, and the subsequent sinking of 12 carcasses in the waters off Cape Nomamisaki. Dense aggregations of unique chemosynthesis‐based fauna had formed around the whale carcasses after 18 months (July 2003). The mytilid mussel Adipicola pacifica was the most abundant macrofaunal species and covered most of the exposed bone surfaces. The general composition of the fauna was similar to that of deep‐water reducing habitats, but none of the species appearing in this study has been found at hydrothermal vents, cold seeps or deep‐water whale falls. A new species of lancelet, which was the first record of the subphylum Cephalochordata from reducing environments, a new species of Osedax; a rarely encountered benthic ctenophore, and a rare gastropod species were discovered at this sperm whale‐fall site. Benthic communities were similar across all the carcasses studied, although the body sizes of the whales were very different. The succession of epifaunal communities was relatively rapid and the sulphophilic stage was considerably shorter than that of other known whale falls.  相似文献   

Temporal variations in lower trophic level biological environments in the northwestern North Pacific Subtropical Gyre from 1950 to 1997     

Atsamon Limsakul  Toshiro Saino  Takashi Midorikawa  Joaquim I. Goes 《Progress in Oceanography》2001,49(1-4)

An examination of large archives (1950–1997) of the oceanographic and atmospheric data from the northwestern North Pacific Subtropical Gyre has revealed clear linkages between atmospheric forcing factors, physical processes and biological events. Large changes in the winter and spring biomass of phytoplankton and macroplankton observed over annual, decadal and inter-decadal time scales could clearly be attributed to climate-related changes in oceanographic processes. Interannual changes in the intensity of the winter-time East Asian Monsoon had a significant impact on the extent of convective overturning, on nitrate inputs into the euphotic zone and the concentrations of chlorophyll a in winter and during the following spring. A prolonged period of deeper winter mixed layers observed from the mid-1970s to the mid-1980s led to a sizeable increase in winter mixed-layer nitrate concentrations. This change resulted in a decrease in winter-time phytoplankton biomass. Spring-time chlorophyll a, in contrast, showed a steady increase during this period. The decline in winter phytoplankton biomass could be attributed to the depths of mixed layer. A deeper mixed layer prevents phytoplankton from remaining in the euphotic zone for long enough to photosynthesize and grow, leaving substantial amounts of nutrients unutilised. However, as a result of stratification of the water column in spring following each of these winters, phytoplankton could take advantage of the enhanced ambient concentrations of nutrients and increase its biomass. Another noteworthy observation for the period from the mid-1970s to the early 1980s is that the western subtropical gyre progressively became phosphate limited. The period of diminishing mixed-layer phosphate concentrations was observed in our study area from the early 1990s onwards was consistent with recent observations at Station ALOHA in the eastern subtropical gyre.  相似文献   

Modified Method for the Analysis of Nitrogen Isotopic Composition of Oceanic Nitrate at Low Concentration   总被引：1，自引：0，他引：1  

Tomoyuki Tanaka  Toshiro Saino 《Journal of Oceanography》2002,58(4):539-546

A method for the determination of the δ¹⁵N of nitrate in seawater described by Cline and Kaplan (1975) has been modified for application to low-level nitrate samples. We have minimized the reagent blank problem by replacing the Devarda's alloy with an aluminum reagent, and have also established a procedure that yields quantitative (93 ± 2%) extraction of nitrogen even at low nitrate levels. Though the amounts and the δ¹⁵N of the blank N varied from one reagent set to another, with these modifications, an overall N blank was reduced to approximately 0.80 ± 0.33 μmole N having an estimated δ¹⁵N value of −1.8‰. After blank and yield corrections, the measured isotopic composition of nitrate differed by approximately 0.1‰ from the actual value while the precision was within ±0.2‰ at the 1.25 μM level. The modified procedure was applied to seawater samples collected from the equatorial Pacific in order to compare the N blanks in field samples with those derived from laboratory experiments. The results support the suitability of the modified approach for isotopic analysis of oceanic nitrate in shallow water. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献