Estimating the Efficiency of the New Seismic Network in Vietnam     

V. Yu. Burmin  Ngo Thi Lu  Phung Thi Thu Hang  Le Quang Khoi 《Seismic Instruments》2018,54(3):281-292

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   

Impact of terrestrial runoff on organic matter,trophic state,and phytoplankton in a tropical,upland reservoir     

Duc Anh Trinh  Thi Nguyet Minh Luu  Quan Hong Trinh  Hai Sy Tran  Tien Minh Tran  Thi Phuong Quynh Le  Thuy Thi Duong  Didier Orange  Jean Louis Janeau  Thomas Pommier  Emma Rochelle-Newall 《Aquatic Sciences - Research Across Boundaries》2016,78(2):367-379

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Non-stationary future return levels for extreme rainfall over Extremadura (southwestern Iberian Peninsula)     

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   

Determining the Concentration of Suspended Sediment in the Lower Đáy River (Northern Vietnam) Using MSI Sentinel 2 High Spatial Resolution Data     

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   

Land grabs and labour: Vietnamese workers on rubber plantations in southern Laos     

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   

Drivers of forest change in Hoa Binh,Vietnam in the context of integration and globalization     

Thi Thuy Hanh Nguyen 《Singapore journal of tropical geography》2019,40(3):452-475

This study identified spatial patterns of forest change in Hoa Binh, Vietnam, from 2005 to 2017 by integrating Landsat data and Geographic Information System (GIS) data. A Multiple Logistic Regression (MLR) model was adapted to analyse drivers of three types of forest change, including (i) deforestation and forest degradation, (ii) forest regrowth and (iii) plantation expansion. The results reveal that accessibility and local economic development were determinants of forest cover dynamics during the integration and globalization period and that increased population pressure and poverty were no longer the main factors in forest cover transition. Several key policies in this time period positively affected forest cover change, triggering private sector participation in developing the forest economy by including households and small and medium enterprises in particular. The findings of this study can provide learning points for the implementation of sustainable forest management policies in other Vietnamese provinces or in neighbouring countries. This research has provided an effective tool for visualizing human‐forest ecosystem interaction, and this tool can be applied to subsequent studies to determine causes of forest cover change at the provincial level in Vietnam.  相似文献   

Using stable isotopes to estimate young water fractions in a heavily regulated,tropical lowland river basin     

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   

Modeling soil desiccation cracking by analytical and numerical approaches     

Amade Pouya  Thi Dong Vo  Sahar Hemmati  Anh Minh Tang 《国际地质力学数值与分析法杂志》2019,43(3):738-763

An energy approach is proposed as a complement to the stress approach commonly considered for investigating soil desiccation cracking. The elastic strain energies before and after crack initiation are estimated by both numerical and analytical solutions. The energy released by cracking is then compared with the fracture energy to discuss crack initiation conditions. This leads to combined energy and stress conditions for crack initiation following Leguillon's theory. An approximate analytical solution is derived from a variational formulation of the porous elastic body equations. A cohesive zone model and finite element code are used to simulate crack propagation in an unsaturated porous body. This analysis shows that the energy criterion is reached before the stress criterion, and this can explain unstable crack propagation at the beginning. The approximate analytical solution allows predicting correctly the crack depth and opening in its initiation stage.  相似文献   

Constraining the cosmological time variation of the fine - structure constant     

Le Duc Thong  Tran van Hung  Nguyen Thi Thu Huong  Ha Huy Bang 《Astrophysics》2010,53(3):446-452

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 C_IV, N_V, Mg_II, Al_III, and Si_IV 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   

Groundwater recharge in suburban areas of Hanoi,Vietnam: effect of decreasing surface-water bodies and land-use change     

Kuroda  Keisuke  Hayashi  Takeshi  Do  An Thuan  Canh  Vu Duc  Nga  Tran Thi Viet  Funabiki  Ayako  Takizawa  Satoshi 《Hydrogeology Journal》2017,25(3):727-742

Over-exploited groundwater is expected to remain the predominant source of domestic water in suburban areas of Hanoi, Vietnam. In order to evaluate the effect on groundwater recharge, of decreasing surface-water bodies and land-use change caused by urbanization, the relevant groundwater systems and recharge pathways must be characterized in detail. To this end, water levels and water quality were monitored for 3 years regarding groundwater and adjacent surface-water bodies, at two typical suburban sites in Hanoi. Stable isotope (δ¹⁸O, δD of water) analysis and hydrochemical analysis showed that the water from both aquifers and aquitards, including the groundwater obtained from both the monitoring wells and the neighboring household tubewells, was largely derived from evaporation-affected surface-water bodies (e.g., ponds, irrigated farmlands) rather than from rivers. The water-level monitoring results suggested distinct local-scale flow systems for both a Holocene unconfined aquifer (HUA) and Pleistocene confined aquifer (PCA). That is, in the case of the HUA, lateral recharge through the aquifer from neighboring ponds and/or irrigated farmlands appeared to be dominant, rather than recharge by vertical rainwater infiltration. In the case of the PCA, recharge by the above-lying HUA, through areas where the aquitard separating the two aquifers was relatively thin or nonexistent, was suggested. As the decrease in the local surface-water bodies will likely reduce the groundwater recharge, maintaining and enhancing this recharge (through preservation of the surface-water bodies) is considered as essential for the sustainable use of groundwater in the area.

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