Long-term monitoring of bottom environments of the continental slope off Otsuchi Bay,northeastern Japan     

Kazumasa Oguri  Yasuo Furushima  Takashi Toyofuku  Takafumi Kasaya  Masahide Wakita  Shuichi Watanabe  Katsunori Fujikura  Hiroshi Kitazato 《Journal of Oceanography》2016,72(1):151-166

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Seasonal variations in the nitrogen isotopic composition of settling particles at station K2 in the western subarctic North Pacific     

Yoshihisa?MinoEmail author  Chiho?Sukigara  Makio?C.?Honda  Hajime?Kawakami  Kazuhiko?Matsumoto  Masahide?Wakita  Minoru?Kitamura  Tetsuichi?Fujiki  Kosei?Sasaoka  Osamu?Abe  Jan?Kaiser  Toshiro?Saino 《Journal of Oceanography》2016,72(6):819-836

Intensive observations using hydrographical cruises and moored sediment trap deployments during 2010 and 2012 at station K2 in the North Pacific Western Subarctic Gyre (WSG) revealed seasonal changes in δ ¹⁵N of both suspended and settling particles. Suspended particles (SUS) were collected from depths between the surface and 200 m; settling particles by drifting sediment traps (DST; 100–200 m) and moored sediment traps (MST; 200 and 500 m). All particles showed higher δ ¹⁵N values in winter and lower in summer, contrary to the expected by isotopic fractionation during phytoplankton nitrate consumption. We suggest that these observed isotopic patterns are due to ammonium consumption via light-controlled nitrification, which could induce variations in δ ¹⁵N(SUS) of 0.4–3.1 ‰ in the euphotic zone (EZ). The δ ¹⁵N(SUS) signature was reflected by δ ¹⁵N(DST) despite modifications during biogenic transformation from suspended particles in the EZ. δ ¹⁵N enrichment (average: 3.6 ‰) and the increase in C:N ratio (by 1.6) in settling particles suggests year-round contributions of metabolites from herbivorous zooplankton as well as TEPs produced by diatoms. Accordingly, seasonal δ ¹⁵N(DST) variations of 2.4–7.0 ‰ showed a significant correlation with primary productivity (PP) at K2. By applying the observed δ ¹⁵N(DST) vs. PP regression to δ ¹⁵N(MST) of 1.9–8.0 ‰, we constructed the first annual time-series of PP changes in the WSG. This new approach to estimate productivity can be a powerful tool for further understanding of the biological pump in the WSG, even though its validity needs to be examined carefully.  相似文献   

Destructive near-fault strong ground motion from the 2016 Kumamoto prefecture,Japan, M7.3 earthquake     

Takashi Furumura 《Landslides》2016,13(6):1519-1524

The sequence of the 2016 Kumamoto, Japan, earthquake, which included an initial M6.5 foreshock on April 14, followed by a larger M7.3 mainshock on April 16, and subsequently occurred high aftershock activity, caused significant damage in Kumamoto and neighboring regions. The near-field strong motion record by strong motion network (K-NET and KiK-net) and the intensity meter network demonstrated clearly the characteristics of the strong ground motion developed by the shallow (H = 12 km), inland earthquake comprising short-time duration (<15–20 s) but large (>1G) ground accelerations. The velocity response spectra of the near-fault motion at Mashiki and Nishihara showed large levels (>300–550 cm/s) in the short-period range (T = 1–2 s), several times larger than that of the near-field record of the destructive 1995 Kobe earthquake (M7.3) and that of the 2004 Mid-Niigata earthquake (M6.8). This period corresponds to the collapse vulnerability of Japanese wooden-frame houses, and is the major cause of severe damage during the Kumamoto earthquake. The response spectra also showed extremely large levels (>240–340 cm/s) in the long-period (T > 3 s) band, which is potentially disastrous for high-rise buildings, large oil storage tanks, etc. to have longer resonant period. Such long-period motion was, for the most parts, developed by the static displacement of the fault movement rather than by the seismic waves radiating from the source fault. Thus, the extreme near-fault long-period motion was hazardous only close to the fault but it attenuated very rapidly away from the fault.  相似文献   

A novel index to evaluate discretization methods:A case study of flood susceptibility assessment based on random forest     

Xianzhe Tang  Takashi Machimura  Wei Liu  Jiufeng Li  Haoyuan Hong 《地学前缘(英文版)》2021,12(6):313-325

The selection of a suitable discretization method(DM)to discretize spatially continuous variables(SCVs)is critical in ML-based natural hazard susceptibility assessment.However,few studies start to consider the influence due to the selected DMs and how to efficiently select a suitable DM for each SCV.These issues were well addressed in this study.The information loss rate(ILR),an index based on the informa-tion entropy,seems can be used to select optimal DM for each SCV.However,the ILR fails to show the actual influence of discretization because such index only considers the total amount of information of the discretized variables departing from the original SCV.Facing this issue,we propose an index,infor-mation change rate(ICR),that focuses on the changed amount of information due to the discretization based on each cell,enabling the identification of the optimal DM.We develop a case study with Random Forest(training/testing ratio of 7:3)to assess flood susceptibility in Wanan County,China.The area under the curve-based and susceptibility maps-based approaches were presented to compare the ILR and ICR.The results show the ICR-based optimal DMs are more rational than the ILR-based ones in both cases.Moreover,we observed the ILR values are unnaturally small(＜1％),whereas the ICR values are obviously more in line with general recognition(usually 10％-30％).The above results all demonstrate the superiority of the ICR.We consider this study fills up the existing research gaps,improving the ML-based natural hazard susceptibility assessments.  相似文献   

Liquid bridge contribution to shear behavior of unsaturated soil: modeling and application to a micromechanics model     

Fukushima  Yo  Higo  Yosuke  Matsushima  Takashi  Otake  Yu 《Acta Geotechnica》2021,16(9):2693-2711

Acta Geotechnica - Liquid bridges in unsaturated soils attach to grain contacts and contribute to strengthening microscopic bonding forces, which leads to macroscopic high strength and stiffness...  相似文献   

Characteristics of ionic components in precipitation in Kitakyushu City,Japan     

Yasuhiro Yamato  Takashi Yamada  Kozo Kido 《Journal of Atmospheric Chemistry》1993,17(4):325-337

Precipitation samples were collected by filtrating bulk sampler in Kitakyushu City, Japan, from January 1988 to December 1990. Volume weighted annual mean of pH was 4.93, but the pH distribution indicated that most probable value lay in the range pH 6.0–6.4. Volume weighted annual mean concentrations of major ionic components were as follows; SO ₄ ^2– : 84.2, NO ₃ ^– : 28.1, Cl^–: 86.3, NH ₄ ⁺ : 45.5, Ca²⁺: 63.3, Mg²⁺: 27.0, K⁺: 3.4, Na⁺: 69.0 µ eq l^–1. The highest concentrations of these ionic components were observed in winter and the lowest occurred in the rainy season. The ratio of ex-SO ₄ ^2– /NO ₃ ^– exhibited the lowest ratio in summer, and the highest ratio in winter. Good correlations were obtained between Cl^– and Na⁺, ex-SO ₄ ²⁺ and ex-Ca²⁺, NO ₃ ^– and ex-Ca²⁺, and NH ₄ ⁺ and ex-SO ₄ ^2– , respectively. However, no correlation between Cl^– and Na⁺ with Ca²⁺ was observed. The relationship of H⁺ with (ex-SO ₄ ^2– + NO ₃ ^– ) - (ex-Ca²⁺ + NH ₄ ⁺ ) indicated positive correlation.  相似文献   

Nucleation,growth and stability of CaAl2Si2O8 polymorphs     

Toshiya Abe  Katsuo sukamoto  Ichiro Sunagawa 《Physics and Chemistry of Minerals》1991,17(6):473-484

By means of in situ observation, the nucleation and growth of triclinic, pseudo-orthorhombic and pseudo-hexagonal CaAl₂Si₂O₈ were investigated and their relative stabilities established. Pseudo-hexagonal and pseudo-orthorhombic CaAl₂Si₂O₈ nucleate prior to anorthite and grow in a supercooled anorthite melt before the latter appears. They either dissolve or transform to anorthite once the latter nucleates and starts to grow. Corundum and mullite also nucleate metastably prior to anorthite in this melt. The liquidus temperatures of the four metastably nucleated phases were determined precisely by in situ measurements of the transformation temperatures from a polyhedral to a rounded morphology. On the basis of the supercooling thus determined, the growth rate versus supercooling relations were measured and analysed for the respective phases. The growth rate of the stable phase is one order of magnitude higher than those of any metastable phases. However, the growth rates of the three CaAl₂Si₂O₈ polymorphs normalized by the viscosities are nearly the same.  相似文献   

Re-evaluation of the large deep earthquake of January 21, 1906     

Katsuyuki Abe 《Physics of the Earth and Planetary Interiors》1985,39(3):157-166

The large deep earthquake of January 21, 1906 is re-evaluated using old seismogram data and updated analysis techniques. From the P and pP-P time data the hypocentre parameters are determined as follows: origin time, 13h 49min 35s; latitude, 33.8°N; longitude, 137.5°E; depth, 340 km. The body-wave magnitude m_B is re-evaluated from the amplitude and periods of P, PP and S waves. The average value of 7.4 is obtained. This value is the smallest among any values assigned previously to this shock, and it is denied that the earthquake is the world's largest deep shock in this century. The focal mechanism is estimated from the P-wave first motions and amplitude distribution of P and S waves. Synthetic body waves are used to constrain the mechanism and to determine the seismic moment. The mechanism solution suggests the down-dip compression typical of this region. A seismic moment of 1.5 × 10²⁷ dyn · cm is obtained. This value and the re-evaluated value of m_B are consistent with the moment-_B relation obtained for other deep earthquakes.  相似文献   

Modeling of the runup heights of the Hokkaido-Nansei-Oki tsunami of 12 July 1993     

Katsuyuki Abe 《Pure and Applied Geophysics》1995,144(3-4):735-745

The Hokkaido-Nansei-Oki earthquake (M _w 7.7) of July 12, 1993, is one of the largest tsunamigenic events in the Sea of Japan. The tsunami magnitudeM _t is determined to be 8.1 from the maximum amplitudes of the tsunami recorded on tide gauges. This value is larger thanM _w by 0.4 units. It is suggested that the tsunami potential of the Nansei-Oki earthquake is large forM _w . A number of tsunami runup data are accumulated for a total range of about 1000 km along the coast, and the data are averaged to obtain the local mean heightsH _n for 23 segments in intervals of about 40 km each. The geographic variation ofH _n is approximately explained in terms of the empirical relationship proposed byAbe (1989, 1993). The height prediction from the available earthquake magnitudes ranges from 5.0–8.4 m, which brackets the observed maximum ofH _n , 7.7 m, at Okushiri Island.  相似文献   

Small scale turbulent diffusion determined with underwater flow visualization     

Takashi Ichiye  James McGrath  Michael Carnes 《Pure and Applied Geophysics》1982,120(4):758-771

Dye plumes were generated at three depths in the seasonal thermocline between 7 and 11 m, 22 km south of Key West on 21 August 1980 and photographed at about 10 second intervals with an underwater camera system. Eleven pairs of consecutive pictures are analyzed to determine the mean current vertical shear and the width of the plumes by positioning reference points relative to the rod attached to the camera system. The relative distances of reference points are calibrated with the stereophotogrammetric method for one pair. The eddy diffusivity is calculated by use of a model of turbulent diffusion developed byTaylor (1921). Its values range from 5 to 25 cm²s^–1 for the plume widths ranging from 33 to 132 cm. The Richardson number is calculated for each pair of pictures with the vertical density gradient estimated from temperature profiles. Its values are higher than the critical value of 0.25 except for one case. The diffusivity was higher by orders of magnitude than the molecular one and indicates the presence of turbulence together with billow like features of the plumes in spite of high Richardson numbers. This suggests that the billow turbulence might be caused by effects of surface gravity waves and not by the Kelvin-Helmholtz instability.  相似文献