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21.
Earthquakes that occur on the territory of Vietnam and especially in the South China Sea are a major hazard to the Vietnam population and infrastructure because of possible destruction and tsunamis, like those took place there in earlier times according to geological data. Therefore, in the early 2000s, the government of Vietnam decided to modernize and expand the network of seismological observations on the territory of the republic. First, it was planned to modernize the seismic network in Vietnam with 20 broadband seismic stations and then increase that number to 30. This raised the problem of the optimal arrangement of these stations in the country to predict earthquakes and study the structure of the crust and upper mantle of Vietnam. The map of Vietnam clearly shows the impossibility of constructing a single optimal observation network to locate earthquake hypocenters over the entire territory, because it is strongly elongated from north to south. Any seismological observation network for such an entire territory will not be optimal. In this case, we can speak about improving local observation networks for some areas, such as the north, center, and south of the country. This work estimates the efficiency (distribution of the minimum representative magnitudes and the error in determining the coordinates of earthquake hypocenters) for the new network of seismological observations in Vietnam, consisting of 30 stations. To improve the quality of the network in central and southern Vietnam, six more seismic stations are proposed. Such a network will allow more accurate determination of the hypocenter parameters in central and southern Vietnam. During the construction of the optimal network configuration, one of the main problems was the choice of an effective network radius. The formula for determining the optimal radius in the seismic observation network is obtained for the case of a uniform distribution of hypocenters in a certain cylindrical region based on the radius of the base and height of this cylinder. In this work, it follows from the formula that the radius of the optimal network should be no less than the radius of the hypocentral region. In our case, the choice of network radius is confined within the state borders and coastline of Vietnam. These restrictions are taken into account in the calculations to optimize the number of seismic stations and the configuration of their location in the country. 相似文献
22.
Francisco Javier Acero Sylvie Parey Thi Thu Huong Hoang Didier Dacunha-Castelle José Agustín García María Cruz Gallego 《水文科学杂志》2017,62(9):1394-1411
Based on a previous study for temperature, a new method for the calculation of non-stationary return levels for extreme rainfall is described and applied to Extremadura, a region of southwestern Spain, using the peaks-over-threshold approach. Both all-days and rainy-days-only datasets were considered and the 20-year return levels expected in 2020 were estimated taking different trends into account: first, for all days, considering a time-dependent threshold and the trend in the scale parameter of the generalized Pareto distribution; and second, for rainy days only, considering how the mean, variance, and number of rainy days evolve. Generally, the changes in mean, variance and number of rainy days can explain the observed trends in extremes, and their extrapolation gives more robust estimations. The results point to a decrease of future return levels in 2020 for spring and winter, but an increase for autumn. 相似文献
23.
Ian G. Baird William Noseworthy Nghiem Phuong Tuyen Le Thu Ha Jefferson Fox 《Singapore journal of tropical geography》2019,40(1):50-70
Since the early 2000s the Lao government has dramatically increased the number of large‐scale land concessions issued for agribusinesses. While studies have documented the social and environmental impacts of land dispossession, the role of Vietnamese labour on these Vietnamese‐owned rubber plantations has not previously been investigated. Taking a political ecology approach, we situate this study at the intersection between ‘land grabbing’ studies and work on ‘labour geographies’. Most of the remittances generated from Vietnamese working in Laos are used for non‐agricultural purposes, with people purposely choosing to not invest in agriculture in Vietnam. Vietnamese labour on Lao plantations still has significant spatial implications, both in Laos and in Vietnam, including through the norms, formal rules and practices introduced at rubber plantations by Vietnamese workers and management, but also through labour regime changes in Vietnam. In Laos, one of the most significant results has been to make certain spaces less welcoming to Lao labour. This study particularly points to the importance of geopolitics, as the close political relationship between Laos and Vietnam, and the fact that Vietnamese companies and managers are involved, is crucial for understanding the particular nature of the labour geographies associated with Vietnamese rubber plantations in Laos. 相似文献
24.
Le Hung Trinh Zablotskii V. R. Nguyen Thi Thu Nga 《Izvestiya Atmospheric and Oceanic Physics》2020,56(12):1645-1651
Izvestiya, Atmospheric and Oceanic Physics - The concentration of suspended sediment is an important parameter in assessing the quality of surface waters. Many studies have shown that reflectance... 相似文献
25.
Anh Duc Trinh Thu Nga Do Virginia N. Panizzo Suzanne McGowan Melanie J. Leng 《水文研究》2020,34(22):4239-4250
The young water fraction of streamflow (Fyw), an important hydrological variable, has been calculated for the first time, for a monsoon-fed coastal catchment in northern Vietnam. Oxygen stable isotopes (δ18O) from six river sites in the Day River Basin (DRB) were analysed monthly, between January 2015 and December 2018. River δ18O signatures showed sine wave variability, reflecting the amount effect and tropical (dry-rainy) seasonality of the region. The δ18O composition of precipitation ranged from −12.67 to +1.68‰, with a mean value of −5.14‰, and in-streamflow signatures ranged from −11.63 to −1.37‰ with a mean of −5.02‰. Fractions of young water (Fyw) were calculated from the unweighted and flow-weighted δ18O composition of samples. Unweighted Fyw ranged between 29 ± 8% and 82 ± 21% with a mean value of 51 ± 19%, and was not significantly different from flow-weighted Fyw (range between 33 ± 25% and 92 ± 73%, mean 52 ± 36%). Both unweighted and flow-weighted Fyw were highest in the middle of stream and lowest in downstream sites, capturing the impacts of landuse changes, hydrology and human activities in the catchment. Our calculations imply that more than a half of rainwater reaches the DRB river mainstream within the first 3 months. The Fyw is much higher than the global average (of one-third) and insensitive to discharge due to the combination of a humid catchment with high rainfall, low storage capacity, flat landscape and an intensive drainage system in the DRB. Also the low discharge sensitivity of Fyw in the DRB implies that the regional hydrology is severely altered by humans. 相似文献
26.
The variation of the fine-structure constant α = e
2 / ħc can be probed by comparing the wavelength of atomic transitions from the redshift of quasars in the Universe and laboratory
over cosmological time scales t ~ 1010 yr. After a careful selection of pairs of lines, the Thong method with a derived analytical expression for the error analysis
was applied to compute the α variation. We report a new constraint on the variation of the fine-structure constant based on the analysis of the CIV, NV, MgII, AlIII, and SiIV doublet absorption lines. The weighted mean value of the variation in α derived from our analysis over the redshift range 0.4939 ≤ z ≤ 3.7 is = ( 0.09 ± 0.07)×10−5. This result is three orders of magnitude better than the results obtained by earlier analysis of the same data on the constraint
on Δα/α . 相似文献
27.
Rubies and sapphires are of both scientific and commercial interest. These gemstones are corundum colored by transition elements within the alumina crystal lattice: Cr3+ yields red in ruby and Fe2+, Fe3+, and Ti4+ ionic interactions color sapphires. A minor ion, V3+ induces slate to purple colors and color change in some sapphires, but its role in coloring rubies remains enigmatic. Trace element and oxygen isotope composition provide genetic signatures for natural corundum and assist geographic typing. Here, we show that V can dominate chromophore contents in Mogok ruby suites. This raises implications for their color quality, enhancement treatments, geographic origin, exploration and exploitation and their comparison with rubies elsewhere. Precise LA-ICP-MS analysis of ruby and sapphire from Mogok placer and in situ deposits reveal that V can exceed 5,000 ppm, giving V/Cr, V/Fe and V/Ti ratios up to 26, 78, and 97 respectively. Such values significantly exceed those found elsewhere suggesting a localized geological control on V-rich ruby distribution. Our results demonstrate that detailed geochemical studies of ruby suites reveal that V is a potential ruby tracer, encourage comparisons of V/Cr-variation between ruby suites and widen the scope for geographic typing and genesis of ruby. This will allow more precise comparison of Asian and other ruby fields and assist confirmation of Mogok sources for rubies in historical and contemporary gems and jewelry. 相似文献
28.
Moe Kyaw Thu Kensaku Tamaki Shin-Ichi Kuramoto Ryuji Tada Saneatsu Saito 《Island Arc》2002,11(1):61-78
Abstract High-resolution seismic stratigraphy of the Yamato Basin, Japan Sea, was successfully established using core-log-seismic data integration. The construction of synthetic seismograms by the combination of physical properties and well-log data from the Ocean Drilling Program (ODP) Site 797 was the key to accomplishing the high-resolution seismic stratigraphy. To achieve resolution comparable with well-log data and core lithology, single channel seismic reflection data taken from ODP underway geophysics were reprocessed, and then carefully compared with synthetic seismogram, core and well log profiles to identify seismic units. Ten seismic stratigraphic units were identified at the site, and seismic stratigraphic interpretation was successfully extended from the site to the nearby area along the Yamato Basin margin. The opal-A/opal-CT (biogenic silica/metastable diagenetic silica) boundary has different appearances at places from strong to weak, and mostly discontinuous. One of the significant results achieved from this study is clear distinction of the opal-A/CT boundary from a very strong reflector, which appears at 22 m below the opal-A/CT boundary. Through well-log and physical properties characterization of the different units, resistivity was found to be the best indicator of diatom content and with gamma-ray it also is an indicator of chert layers in the opal-CT zone. Velocity is not greatly effected by diatom ooze in the opal-A zone, however, it shows strong peaks and has an indirect relationship with gamma-ray in the opal-CT zone. Finally, successful correlation of Gamma-ray Attenuation Porosity Evaluator density and resistivity peaks with strong seismic reflectors from upper and lower stratified layers may provide new information on the late Neogene paleoceanography of the Japan Sea in high-resolution scale. 相似文献
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30.
Viscous Behaviour of Soft Clay and Inducing Factors 总被引：1，自引：1，他引：0
Thu Minh Le Behzad Fatahi Hadi Khabbaz 《Geotechnical and Geological Engineering》2012,30(5):1069-1083
As a result of the scarcity of land for construction, a number of projects to construct man-made islands or to expand lands over soft grounds keeps increasing. Creep behaviour of soft ground has been considered as a challenging issue for engineers and researchers for many years. A number of studies have focused on the method to predict the creep deformation of the ground under a construction site. However, there is no unified theory to clearly explain the mechanism of soil creep deformation of soils. Results of the critical review in this paper indicate that the causes of soil creep can be categorised into five main groups, namely (a) the breakdown of the inter-particle bonds, (b) sliding between the soil particles, (c) water flow from micro-pores to macro-pores (d) the deformation due to the structural viscosity and (e) the deformation due to the jumping of bonds. This paper presents these mechanisms in details with an effort to recommend an enhanced explanation for the creep compression mechanisms of clays. 相似文献