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101.
—We examine the possibility of seismic anisotropy in the asthenosphere due to present plate motion using SKS splitting results. The fast directions of anisotropy correlate weakly with the directions of the absolute plate motion (APM) for all APM models. Weak correlation indicates the possibility of asthenospheric anisotropy as well as frozen anisotropy in the lithosphere. Detection of strain rate dependence of anisotropy is helpful to further conclusion of the problem. The selection of reference frame is important to describe shear deformation in the asthenosphere beneath continent due to plate motion. The behavior of hot spots to the mesosphere, fixed or drifted by mantle return flow, is a key of the selection of the reference frame. For the NNR-NUVEL1 model, APM correlated anisotropy appears only at plate velocity faster than 1.4 cm/yr. It suggests the new possibility of the formation of asthenospheric anisotropy in addition to frozen anisotropy in the lithosphere. A critical plate velocity for the formation of anisotropy can be caused by the dislocation-diffusion transition as a function of strain rate on a deformation mechanism map of the upper mantle olivine. 相似文献
102.
Kuju Volcano lies near Aso Caldera at the center of Kyushu Island, western Japan. After a few hundred years of dormancy,
a phreatic explosion accompanied by a small ash eruption occurred on 11 October 1995. This study was undertaken to determine
the subsurface seismic velocity structure associated with the active magmatic regime in the Kuju volcanic region. The three-dimensional,
upper crustal, P-wave velocity structure beneath Kuju Volcano was determined using methods for the simultaneous inversion
of P-wave arrival times from local earthquakes in and around the Kuju volcanic region for velocities and hypocentral parameters.
Results reveal two shallower low-velocity anomalies located in the northern and southern parts of Kuju Volcano, consistent
with the presence of significant negative Bouguer gravity anomalies. In addition, a high-velocity anomaly is located approximately
5 km northwest of Mt. Kuju, one of the domes in Kuju Volcano. Beneath this high-velocity anomaly, a low-velocity anomaly is
present. This velocity structure suggests a magmatic regime that has a lid consisting of cooled solid material overlying a
chamber of partially molten material.
Received: 23 September 1997 / Accepted: 20 June 1998 相似文献
103.
Jota Kanda Shiho FujiwaraHiroshi Kitazato Yoshihiro Okada 《Progress in Oceanography》2003,57(1):17-29
Seasonal variations in the primary production regime in the upper water column were assessed by shipboard observations using hydrocasts and natural fluorescence profiling at a fixed station in the central part of Sagami Bay, Japan. The observations were conducted as a part of ‘Project Sagami’ dedicated to the interdisciplinary study of seasonality in bathyal benthic populations and its coupling with water column processes. Based on the time-series observations at intervals of about 1 to 2 months, primary productivity in terms of chlorophyll abundance appeared to be elevated during the spring of 1997, but the observed peaks of biomass were much less significant in the spring of 1998. Meanwhile, the organic matter flux, as indicated by sediment trap data and benthic observations, had a significant peak in the spring of 1998 as well, and its magnitude was comparable to that in 1997. Satellite images of ocean color obtained during the spring of 1997 indicate the importance of events with time scales much shorter than a month, and suggest qualitative differences in the phytoplankton community in the euphotic zone for each bloom event during this period. The possible mechanisms that could yield the spring maximum of material input to the benthic community are discussed. 相似文献
104.
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
105.
Observations of wind velocity and temperature fluctuations were made in the nocturnal surface inversion layer over a paddy field. A remarkable wave-like motion of about 8 min period was seen in horizontal wind speed and standard deviation of vertical wind velocity. In addition, fluctuations of horizontal wind speed and anticlockwise rotation of wind direction with a period of about 30 min were found by power spectral analysis. The phenomena persisted for more than 2 hours. Similar phenomena were also observed at a coastal site at a distance of about 10 km from the paddy field. 相似文献
106.
The first known solution of the title problem is presented. The Ritz method is used, with algebraic polynomials forming the set of trial functions. The condition that all three components of displacement be zero at the four corners is straightforwardly enforced. Numerical studies show that the convergence is relatively slow, requiring more terms than for shells which are completely free. The class of problems studied includes independent, constant curvature in each of the directions parallel to the edges, yielding vibration modes which fall into one of four symmetry classes, with symmetry or antisymmetry of the displacements existing with respect to each of the two symmetry axes of the problem. Detailed results are given for the frequencies and mode shapes of the first two modes of each symmetry class for shells having square planform and circular cylindrical, spherical and hyperbolic paraboloidal curvatures. Accuracy of the results is partially established by comparison with other previously published, accurate results for the corner supported flat square plate. 相似文献
107.
Kotaro Yonezu Takushi Yokoyama Yoshihiro Okaue Akira Imai Koichiro Watanabe 《Resource Geology》2007,57(4):400-408
In order to elucidate the formation mechanism of low‐sulfidation epithermal gold deposit, the adsorption of [Au(S2O3)2]3? (a model compound for gold(I) complex ion) on alumina gel (a model compound for the aluminum‐bearing minerals) and change in chemical state of [Au(S2O3)2]3? after adsorption on the surface of alumina gel were investigated as a basic model experiment. In the pH range from 4 to 6, the amount of [Au(S2O3)2]3? adsorbed on alumina gel decreased with increasing pH and decreased drastically between pH 6 and 7, and then approached zero above pH 8 at 30°C. At 60°C, the amount of gold adsorbed above pH 7 was enhanced compared with that at 30°C. This adsorption tendency indicates that [Au(S2O3)2]3? is mainly adsorbed by electrostatic interaction between negative charges of [Au(S2O3)2]3? and positive charges of alumina gel because of its isoelectric point around pH 9. The chemical state of gold after adsorption of [Au(S2O3)2]3? on alumina gel was examined using X‐ray absorption near edge structure (XANES). The result showed that [Au(S2O3)2]3? was spontaneously reduced to elemental gold even in the absence of specific reducing agents after adsorption on alumina gel. This reduction reaction might occur by two steps: (i) disproportionation of the adsorbed [Au(S2O3)2]3? at the surface of alumina gel, and (ii) spontaneous reduction of the resulting gold(III) complex ions on the surface of alumina gel. The experimental results suggest that aluminum plays an important role in the concentration of gold(I) complex ions and subsequent reduction of gold during the formation of low‐sulfidation epithermal gold deposits. 相似文献
108.
Neda Tavakoli Nahid Shabanian Hossein Azizi Franz Neubauer Yoshihiro Asahara 《International Geology Review》2020,62(13-14):1658-1676
ABSTRACT The Boein–Miandasht Complex (BMC) is a part of the Sanandaj–Sirjan metamorphic basement and is cut by gabbroic to granitoid bodies. These intrusive bodies comprise gabbro, gabbro–diorite associated with fine-grained, in part porphyritic leucocratic granitoids. Zircon U–Pb dating of representative gabbro–diorite samples yielded ages of 166.4 ± 1.8 Ma and 163.5 ± 6.3 Ma (Callovian, the latest stage of the Middle Jurassic). Mineral chemistry of the gabbro–diorites shows a homogeneous composition of the main minerals, main augite to diopside clinopyroxene and plagioclase (~An17–59). Moreover, low AlZ/TiO2 ratios of the clinopyroxene grains suggest that the rocks were generated in a within-plate tectonic regime. The SiO2 contents of the gabbro-diorite rocks are between 46.36 and 55.61 wt. %, Al2O3 ranges from 7.57 to 17.98 wt. %. The TiO2 contents vary from 1.18 to 3.65 wt. %, Fe2O3 from 7.41 to 12.95 wt. %, the MgO ranges between 3.49 and 15.75 wt. %, Na2O from 0.65 to 5.08 wt. % and K2O from 0.48 to 1.08 wt. %. These rocks mostly plot in the alkali-gabbro field. Compared to chondrite are characterized by enrichment of LREEs over HREE, enrichment of LIL elements (e.g. Rb, Sr and Ba) and obvious positive anomalies of Nb and Ti. Based on the chemical composition, and mineral composition, this complex was generated in an extensional tectonic regime by partial melting of the hot asthenospheric mantle which is not more consistent with previous models which have suggested for SaSZ evolution in before. 相似文献
109.
Carbon isotope stratigraphy of the Late Jurassic and earliest Cretaceous was revealed from Torinosu‐type limestone, which was deposited in a shallow‐marine setting in the western Paleo‐Pacific, in Japan. Two sections were examined; the Nakanosawa section of the late Kimmeridgian to early Tithonian age (Fukushima Prefecture, Northeast Japan), and the Furuichi section of the late Kimmeridgian to early Berriasian age (Ehime Prefecture, Southwest Japan). The age‐model was established using Sr isotope ratio and fossil occurrence. The limestone samples have a low Mn/Sr ratio (mostly <0.5) and lack a distinct correlation between δ13C and δ18O, indicating a low degree of diagenetic alteration. Our composite δ13C profile from the two limestone sections shows three stratigraphic correlation points that can be correlated with the profiles of relevant ages from the Alpine Tethyan region: a large‐amplitude fluctuation (the lower upper Kimmeridgian, ~152 Ma), a positive anomaly (above the Kimmeridgian/Tithonian boundary, ~150 Ma), and a negative anomaly (the upper lower Tithonian, ~148 Ma). In addition, we found that δ13C values of the Torinosu‐type limestone are ~1‰ lower than the Tethyan values in the late Kimmeridgian. This inter‐regional difference in δ13C values is likely to have resulted from a higher productivity and/or an organic burial in the Tethyan region. The difference gradually reduces and disappears in the late Tithonian, where the Tethyan and our δ13C records show similar stable values of 1.5–2.0‰. This isotopic homogenization is probably due to changes in the continental distribution and the global ocean circulation, which propagated the 13C‐depleted signature from the larger Paleo‐Pacific to the smaller Tethys Ocean during this time. 相似文献
110.
Assessment of turbulence closure models for resonant inertial response in the oceanic mixed layer using a large eddy simulation model 总被引:1,自引:0,他引:1
Large eddy simulation (LES) of the resonant inertial response of the upper ocean to strong wind forcing is carried out; the
results are used to evaluate the performance of each of the two second-order turbulence closure models presented by Mellor
and Yamada (Rev Geophys Space Phys 20:851–875, 1982) (MY) and by Nakanishi and Niino (J Meteorol Soc Jpn 87:895–912, 2009) (NN). The major difference between MY and NN is in the formulation of the stability functions and the turbulent length scale,
both strongly linked with turbulent fluxes; in particular, the turbulent length scale in NN, unlike that in MY, is allowed
to decrease with increasing density stratification. We find that MY underestimates and NN overestimates the development of
mixed layer features, for example, the strong entrainment at the base of the oceanic mixed layer and the accompanying decrease
of sea surface temperature. Considering that the stability functions in NN perform better than those in MY in reproducing
the vertical structure of turbulent heat flux, we slightly modify NN to find that the discrepancy between LES and NN can be
reduced by more strongly restricting the turbulent length scale with increasing density stratification. 相似文献