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41.
42.
Masakazu Niwa Koji Shimada Shuji Terusawa Akira Goto Nariaki Nishiyama Toru Nakajima Takanori Ishihara Hiroaki Hakoiwa 《Island Arc》2024,33(1):e12516
This study investigated geological evidence for near-surface crustal deformation in a high-strain shear zone that has been geodetically identified but which is not associated with obvious tectonic landforms. Fieldwork was conducted in the east–west-trending southern Kyushu high-strain shear zone (SKHZ), Japan, focusing mainly on occurrences of fracture zones, which are defined by a visible fracture density of >1 per 10 cm2 and are commonly associated with cataclasite, fault breccia, and gouge. The area in which east–west-trending fracture zones are dominant is restricted to the east–west-trending, ~2-km-wide aftershock area of the 1997 Northwestern Kagoshima Earthquakes. Analysis of slip data from minor faults using the multiple inverse method, irrespective of whether the faults are in fracture zones, reveals that the area where the calculated main stress field is consistent with the current stress field estimated from focal-mechanism solutions of microearthquakes is restricted to the east–west-trending aftershock area. This finding for the SKHZ contrasts with the case of the Niigata–Kobe Tectonic Zone, which is a major strain-concentration zone with many exposed active faults in central Japan and for which the stress field estimated using fault-slip data is considered to be uniform and coincides with the current stress field. The cumulative amount of displacement estimated from the areal density of fracture zones in the SKHZ study area is smaller than that estimated from geodetically measured strain rates. Investigations based on slip data from minor faults and fracture-zone occurrence could help to identify concealed faults that are too small to generate tectonic landforms but which are sufficiently large to trigger major earthquakes. 相似文献
43.
J. Nakajima Y. Koyama M. Sekido N. Kurihara T. Kondo M. Kimura N. Kawaguchi 《Experimental Astronomy》2001,11(1):57-69
We report on the detection of VLBI fringes from quasars by a new VLBI system operating at 1 Gbps (1024 Mbits-per-second). Newly developed 1024 Msps (mega sample-per-second) AD samplers and 1024 Mbps recorders were used for the observations. A correlator with external buffers was used for the 1024 Mbps correlation processing of the tapes data.Our new VLBI system enabled 1024 Mbps VLBI, and this allowed the sampling of a 512 MHz bandwidth from a radio telescope receiver. This is the highest sampling speed ever used for VLBI, and the widest bandwidth used for VLBI observation. Initial sensitivity as evaluated by SNR comparison with earlier VLBI systems produced results to matched the expanded bandwidth. In our first observations, simultaneous optical fibre linked real-time VLBI observations were made to check the validity of data and precisely detemine the clock offsets among the radio telescopes. 相似文献
44.
From 200 GRF (gradual rise and fall) bursts which have been recorded with the 17 GHz interferometer at Nobeyama, we deduce the following characteristics of GRF bursts: (1) Sources of GRF bursts are broader, less circularly polarized than those of impulsive bursts. (2) The sources are potentially of bipolar structure and have the peak brightness near the position at which the sense of circular polarization changes. (3) The association of GRF bursts with type III bursts, which are indicative of nonthermal electron acceleration, is significantly poorer than that of impulsive bursts.It is suggested that the sources of GRF bursts or generally of thermal bursts lie relatively high in the solar atmosphere possibly near the top of magnetic loops or arches which divide two regions of opposite magnetic polarity. 相似文献
45.
Robert Frouin Pierre-Yves Deschamps Lydwine Gross-Colzy Hiroshi Murakami Takashi Y. Nakajima 《Journal of Oceanography》2006,62(3):331-337
Top-of-atmosphere reflectance measured above the ocean in the visible and near infrared, after correction for molecular scattering,
may be linearly combined to retrieve surface chlorophyll-a abundance directly, without explicit correction for aerosol scattering
and absorption. The coefficients of the linear combination minimize the perturbing effects, which are modeled by a polynomial,
and they do not depend on geometry. The technique has been developed for Global Imager (GLI) spectral bands centered at 443,
565, 667, and 866 nm, but it is applicable to other sets of spectral bands. Theoretical performance is evaluated from radiation-transfer
simulations for a wide range of geophysical and angular conditions. Using a polynomial with exponents of −2, −1, and 0 to
determine the coefficients, the residual influence of the atmosphere on the linear combination is within ±0.001 in most cases,
allowing chlorophyll-a abundance to be retrieved with a root-mean-squared (RMS) error of 8.4% in the range 0.03–3 mgm−3. Application of the method to simulated GLI imagery shows that estimated and actual chlorophyll-a abundance are in agreement,
with an average RMS difference of 32.1% and an average bias of −2.2% (slightly lower estimated values). The advantage of the
method resides in its simplicity, flexibility, and rapidity of execution. Knowledge of aerosol amount and type is avoided.
There is no need for look-up tables of aerosol optical properties. Accuracy is adequate, but depends on the polynomial representation
of the perturbing effects and on the bio-optical model selected to relate the linear combination to chlorophyll-a abundance.
The sensitivity of the linear combination to chlorophyll-a abundance can be optimized, and the method can be extended to the
retrieval of other bio-optical variables. 相似文献
46.
Hideo Nakajima 《Journal of Oceanography》1976,32(6):267-270
The relation between the initial spatial scale and the life time, of turbulent small masses of sea water produced at the strait or the interface between two water masses, is investigated analytically. In the analysis, their initial shape is assumed to be expressed as the Rankine vortex, and the horizontal eddy viscosity coefficient to obey then-th power-law with respect to scale. Particularly in the case ofn=4/3 (the 4/3 power-law), it is obtained that the life time is proportional to the 2/3 power of the initial scale. The proportional coefficient can be determined in the present analysis except a parameter related to the energy dissipation rate of each sea area. 相似文献
47.
48.
Kohki Yoshida Toru Nakajima Yuki Matsumoto Ai Osaki Lalit Kumar Rai Jarrett W. Cruz Harutaka Sakai 《Island Arc》2021,30(1):e12408
Bengal Fan Miocene sediments were collected during International Ocean Discovery Program Expedition 354 and investigated using petrographic and detrital garnet chemistry analyses. The Miocene Siwalik Group, which is composed of sediments deposited in the Himalayan foreland basin, was also analyzed for comparison with the Bengal Fan data for the provenance change during the Miocene. Our petrographic analyses revealed that the Miocene sediments of the Bengal Fan and Siwalik Group consist predominantly of Higher Himalayan Crystalline (HHC)-derived detritus such as chloritoid, staurolite, sillimanite, and/or kyanite, which appear among the accessory minerals. The chemistry of the detrital garnet varies across the stratigraphy; most of the garnet is rich in almandine and poor in spessartine and pyrope. However, pyrope-rich garnet, which is considered to originate from the HHC core (granulite facies), was found in the lower to upper Miocene deposits. The deposition of HHC-derived detrital garnet began before the Middle Miocene (15 Ma) and before the Late Miocene (10–9 Ma) in the Siwalik Group. The Bengal Fan data, by contrast, indicated that pyrope-rich garnet appeared in the Early Miocene (17.3 Ma) and Late Miocene (8.5–6.5 Ma). We conclude that the Bengal Fan sediments record the erosion of the HHC zone since the Early Miocene that appears in the Siwalik sediments. Furthermore, we found that the HHC-derived inputs decreased from the late Middle Miocene (12 Ma) to the early Middle Miocene (10 Ma) in both the Nepal Himalaya foreland basin and the Bengal Fan. The disappearance of the HHC-derived detritus is probably the result of dilution by Lesser Himalayan detritus, which suggests that the Lesser Himalayan zone, which is composed of metamorphosed and unmetamorphosed sedimentary rocks, was uplifted. 相似文献
49.
50.
Quantitative research on composition, biomass and production rates of zooplankton community is crucial to understand the trophic structure in coral reef pelagic ecosystems. In the present study, micro‐ (35–100 μm) and net‐ (>100 μm) metazooplankton were investigated in a fringing coral reef at Tioman Island of Malaysia. Sampling was done during the day and night in August and October 2004, and February and June 2005. The mean biomass of total metazooplankton (i.e. micro + net) was 3.42 ± 0.64 mg C·m?3, ranging from 2.32 ± 0.75 mg C·m?3 in October to 3.26 ± 1.77 mg C·m?3 in August. The net‐zooplankton biomass exhibited a nocturnal increase from daytime at 131–264% due to the addition of both pelagic and reef‐associated zooplankton into the water column. The estimated daily production rates of the total metazooplankton community were on average 1.80 ± 0.57 mg C·m?3·day?1, but this increased to 2.51 ± 1.06 mg C·m?3·day?1 if house production of larvaceans was taken into account. Of the total production rate, the secondary and tertiary production rates were 2.20 ± 1.03 and 0.30 ± 0.06 mg C·m?3·day?1, respectively. We estimated the food requirements of zooplankton in order to examine the trophic structure of the pelagic ecosystem. The secondary production may not be satisfied by phytoplankton alone in the study area and the shortfall may be supplied by other organic sources such as detritus. 相似文献