Estimation of crustal structure from observed group velocities ofPL-waves in Japan     

Masayuki Fujita  Keiichi Nishimura 《Pure and Applied Geophysics》1991,137(3):233-249

Forward modelling of the crustal structure of the eastern Honshu Island, Japan, was made based on the group velocities ofPL-waves in the period range of 20–30 s. The observed values of group velocity were obtained by appling the multiple filter technique to the seismograms for earthquakes with the epicentral distance ranging from 500 to 1000 km. The theoretical values were calculated using Oliver and Major's method to find the best fit dispersion curve in the least-squares sense. The obtained structural model has considerably high crustal velocities compared to other previous models. It was shown that thePL-wave group velocity in the period range of interest was most sensitive to seismic velocities of the center of the crust. Numerical experiments confirmed the applicability of the approximation methods employed to obtain both observed and theoretical group velocities.  相似文献   

Estimation of crustal structure in central and west Japan from waveform modeling of regionalPL waves     

Masayuki Fujita  Keiichi Nishimura 《Pure and Applied Geophysics》1993,140(4):569-592

An inverse method of modeling the regionalPL waveform with the predominant period of about 20 s was developed to estimate the averageS-velocity structure of the upper crust. Applicability of the waveform modeling was confirmed by the results of the numerical experiments: thePL waveform is most sensitive to theS velocity in the upper crust, whereas it is not affected significantly by errors involved in the focal mechanism solution and focal depth determination when thePL wave is well developed. The method was applied to the observed seismograms recorded in central Japan from the earthquakes with epicentral distances 300–500 km. As a result, distinct regional differences were found in the upper crustalS velocity; in particular, between the southern Shikoku district, west Japan, and the southern Chubu district, central Japan, and between the mountainous and the coastal areas in the southern Chubu district. These differences are in agreement with the general features ofP-velocity structures obtained by explosion experiments and by analyses of natural earthquakes. Our method is effective to the extent that the crustal structure along the propagation path can be assumed a horizontally layered structure; it is not applicable when the sensitivity of thePL waveform to the error in the focal mechanism solution is exceptionally high.  相似文献   

Hydroxy acids in Antarctic lake sediments and their geochemical significance     

Genki I. Matsumoto  Kunihiko Watanuki  Tetsuya Torii 《Organic Geochemistry》1988,13(4-6)

Hydroxy acids in sediments of Lakes Bonney, Fryxell, Joyce and Vanda, and unnamed ponds (B2, NF1, NF2 and L4) as well as in cyanobacterial mats from the McMurdo Sound region of southern Victoria Land in Antarctica have been studied to clarify their features and elucidate their source organisms. Normal and branched (iso and anteiso) 2-hydroxy acids were found in all the samples studied with the predominance of even- and odd-carbon numbers, respectively. The most dominant 2-hydroxy acids in the sediments were mainly short-chain components (<C₂₀). Normal and branched 3-hydroxy acids were detectewith the predominance of even- and odd-carbon numbers, respectively, in total concentrations between 0.48 and 53 μg/g of dry sediment. (ω-1)-Hydroxy acids were all long-chains (C₂₂, C₂₄, C₂₆, C₂₈ and C₃₀). 9,10-Dihydroxyhexadecanoic and/or 9,10-dihydroxyoctadecanoic acids were identified in all the sediments and a cyanobacterial mat. The composition of hydroxy acids differ considerably among the lakes and ponds, suggesting the difference of source organisms. These 2-, 3- and (ω-1)-hydroxy, and 9,10-dihydroxy acids may be derived from cyanobacteria and microalgae, in addition to non-photosynthetic microorganisms. Cyanobacteria and microalgae which are widely distributed in the world, may be important sources of hydroxy acids in the natural environments.  相似文献   

Partitioning Eddy-Covariance Methane Fluxes from a Shallow Lake into Diffusive and Ebullitive Fluxes   总被引：1，自引：0，他引：1  

Hiroki Iwata  Ryuichi Hirata  Yoshiyuki Takahashi  Yuichi Miyabara  Masayuki Itoh  Kotaro Iizuka 《Boundary-Layer Meteorology》2018,169(3):413-428

Methane (\(\mathrm {CH}_{4}\)) is known to be emitted from lakes to the atmosphere via processes such as diffusion and ebullition (i.e., bubble emission). We developed a practical method for partitioning eddy-covariance \(\mathrm {CH}_{4}\) fluxes from a shallow lake into diffusive and ebullitive fluxes using a wavelet analysis based on local scalar similarity between the \(\mathrm {CH}_{4}\) concentration and other reference scalars, such as the air temperature or water vapour concentration, in the wavelet time-scale domain, with the hypothesis that similar and dissimilar fluctuation components are related to diffusive and ebullitive \(\mathrm {CH}_{4}\) fluxes, respectively. Our method is applied to approximately two weeks of data obtained at a shallow mid-latitude lake. The partitioned diffusive flux has a physically sound relationship with wind speed, supporting the validity of the method. The ratio of the diffusive flux to the total flux is typically 0.11 with flow from an area of steady bubble emission, but otherwise 0.36. Further validation is required using a larger dataset and data from other lakes. The proposed method can be easily applied to historical data because it requires only 10-Hz data of \(\mathrm {CH}_{4}\) concentration and other reference scalars, along with an empirical parameter.  相似文献   

Development of a numerical model for nitrates in groundwater in the reservoir area of the Komesu subsurface dam, Okinawa, Japan   总被引：1，自引：0，他引：1  

Shuhei Yoshimoto  Takeo Tsuchihara  Satoshi Ishida  Masayuki Imaizumi 《Environmental Earth Sciences》2013,70(5):2061-2077

A numerical model consisting of simplified equations was developed to simulate nitrate concentrations in groundwater in a reservoir area of a subsurface dam in a Quaternary limestone region. The model was composed of a water balance sub-model and a nitrogen balance sub-model; the water balance sub-model was built from tank models which can express the quick dilution near caves and the effect of dam construction; and the nitrogen balance sub-model was made to represent changes in nitrogen forms and movement of nitrogen in the soil and aquifer zones. The model was calibrated and verified by observed data before and after the dam construction and then applied to a predictive simulation under a simple assumption that rainfall descends gradually. The model seemed applicable to long-term prediction of changes in NO₃-N in the reservoir area.  相似文献   

Intensity variations of the postnoon auroral bright spots observed at Zhongshan Station, Antarctica on August 8, 1999     

艾勇  邓晓华  刘瑞源  杨惠根 《极地研究(英文版)》2002,13(1)

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Gas stripping by radiation drag from an interstellar cloud     

Jun'ichi Sato  Masayuki Umemura  Keisuke Sawada  Shingo Matsuyama 《Monthly notices of the Royal Astronomical Society》2004,354(1):176-182

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A huge filamentary structure at z= 0.55 and star formation histories of galaxies at z < 1     

Masayuki Tanaka  Takako Hoshi  Tadayuki Kodama  Nobunari Kashikawa 《Monthly notices of the Royal Astronomical Society》2007,379(4):1546-1556

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Galactic winds from primeval galaxies     

Masao Mori  Masayuki Umemura 《Astrophysics and Space Science》2007,311(1-3):111-115

Ultra-high resolution hydrodynamic simulations using 1024³ grid points are performed of early supernova burst in a forming galaxy, with properties similar to those inferred for Lyman α emitters (LAEs) and Lyman Break Galaxies (LBGs). We show that, at the earliest stages of less than 300 Myr, continual supernova explosions produce multitudinous hot bubbles and cooled H(I) shells in-between. The H(I) shells radiate intense Lyman α (Lyα) emission like LAEs. We found that the bubbly structures produced are quite similar to the observed features in the Lyα surface brightness distribution of the extended LAEs. After 1 Gyr, the galaxies are dominated by stellar continuum radiation and then resemble the LBGs. At this point, the abundance of heavy elements appears to be solar. After 13 Gyr, these galaxies resemble present-day ellipticals.  相似文献   

Enhanced Dissolved Organic Matter Recovery from Saltwater Samples with Electrodialysis     

Luke R. Chambers  Ellery D. Ingall  Emily M. Saad  Amelia F. Longo  Masayuki Takeuchi  Yuanzhi Tang  Claudia Benitez-Nelson  Sheean T. Haley  Sonya T. Dyhrman  Jay Brandes  Aron Stubbins 《Aquatic Geochemistry》2016,22(5-6):555-572

Complexities associated with dissolved organic matter (DOM) isolation from seawater have hampered compositional characterization of this key component of global carbon and nutrient cycles. DOM isolation efficiency by electrodialysis (ED) from salt-containing waters was optimized and evaluated on samples including coastal ocean seawater, open ocean seawater, artificial seawater from axenic cultures of marine phytoplankton, and artificial seawater samples containing standard compounds of different molecular sizes and charge. ED was performed with a system optimized for processing 2–10 L sample volumes. Additionally, the combination of ED and solid-phase extraction, using Bond Elut PPL exchange resin, was evaluated. Using only ED, the following DOC recoveries were achieved: coastal seawater, 71.3 ± 6.5 %; open ocean, 50.5 ± 3.1 %; phytoplankton cultures, 70.3 ± 12.5 %; glucose, 90.2 ± 2.1 %; EDTA, 67.5 ± 9.9 %; and vitamin B₁₂, 98.3 ± 1.6 %. With the combination of PPL and ED techniques, an average DOC recovery of 76.7 ± 2.6 % was obtained for coastal seawater, but this recovery was not statistically different from seawater recoveries using only ED. Comparison of C/N ratios and fluorescence excitation emission matrices taken at the beginning and end of the recovery process for coastal samples processed using only ED indicated that the final recovered material was representative of the DOM present in the original samples. Typical recoveries using combined PPL and ED exceed those of previous isolation methods.  相似文献