Modeling undertow due to random waves

A numerical model of undertow due to random waves is developed. The model includes three sub-models: (i) a model for multi-directional and multi-frequency random wave transformation, (ii) a surface roller evolution model, and (iii) a model for calculating the vertical distribution and the mean value of the undertow velocity. The calculation of wave trough level is performed based on a theory for the wave asymmetry. The model was successfully validated against small- and large-scale laboratory experiments. Thus, the model is expected to provide reliable input for the modeling of sediment transport and morphological change due to waves and currents.     

越南西北部地区Sinh Quyen岩组副片麻岩的锆石年龄及其地质意义

在大地构造位置上, 越南西北部地区是古特提斯造山带东段重要的组成部分, 并记录了印支陆块和华南板块碰撞拼合历史.其构造归属是厘定该地区古特提斯板块缝合带位置的关键.报道了出露的基底岩石Sinh Quyen岩组副片麻岩的碎屑锆石年龄, 探讨其沉积物源和归属问题.该岩组主要由长英质副片麻岩和混合岩等岩石类型构成, 被认为是越南西北部中元古代—古元古代基底岩石.采用LA-ICP-MS锆石U-Pb定年方法分析了3个长英质副片麻岩样品的116粒碎屑锆石.123个分析点锆石年龄的统计结果显示, 碎屑锆石形成时代主要集中在约1.8 Ga左右, 有少量约2.2~3.0 Ga中太古代碎屑锆石, 暗示Sinh Quyen副片麻岩沉积物源主要为早古元古代基底岩石.基底岩石在形成时间上与华南板块古老基底相似, 推断Sinh Quyen岩组在构造归属上可能来自华南板块.部分碎屑锆石边部记录约250 Ma变质增生作用, 可能与华南板块—印支板块的印支期拼合有关, 记录了古特提斯造山作用.      

EM and GPR investigations of contaminant spread around the Hoc Mon waste site,Vietnam

This paper is presenting the results from near-surface geophysical surveys near the waste site of Hoc Mon in southern Vietnam where leachate contamination has been recognized at the surface. Using EM and GPR surveys, we were able to determine the lateral extent of a contaminated area of high electrical conductivity and have identified channels that concentrate the contaminant flow. The simple relationship between the electrical resistivity and the leachate concentration is suggested and estimated the in situ leachate concentration from the inversion of the EM data; values are as high as 40%. Thanks to a permeability barrier leachate flow is confined to the shallow subsurface, making it easier to apply possible site remediation projects.     

A novel hybrid approach of Bayesian Logistic Regression and its ensembles for landslide susceptibility assessment

Abstract

A novel artificial intelligence approach of Bayesian Logistic Regression (BLR) and its ensembles [Random Subspace (RS), Adaboost (AB), Multiboost (MB) and Bagging] was introduced for landslide susceptibility mapping in a part of Kamyaran city in Kurdistan Province, Iran. A spatial database was generated which includes a total of 60 landslide locations and a set of conditioning factors tested by the Information Gain Ratio technique. Performance of these models was evaluated using the area under the ROC curve (AUROC) and statistical index-based methods. Results showed that the hybrid ensemble models could significantly improve the performance of the base classifier of BLR (AUROC?=?0.930). However, RS model (AUROC?=?0.975) had the highest performance in comparison to other landslide ensemble models, followed by Bagging (AUROC?=?0.972), MB (AUROC?=?0.970) and AB (AUROC?=?0.957) models, respectively.     

Daily precipitation concentration in Central Coast Vietnam

Theoretical and Applied Climatology - Empirical frequency distribution of daily precipitation amounts can be fitted by a negative exponential distribution, because anywhere there are many small...     

An analysis of coastal erosion in the tropical rapid accretion delta of the Red River, Vietnam

The largest plain in the North Vietnam has formed by the redundant sediment of the Red River system. Sediment supply is not equally distributed, causing erosion in some places. The paper analyzes the evolvement and physical mechanism of the erosion. The overlay of five recent topographical maps (1930, 1965, 1985, 1995, and 2001) shows that sediment redundantly deposits at some big river mouths (Ba Lat, Lach, and Day), leading to rapid accretion (up to 100 m/y). Typical mechanism of delta propagation is forming and connecting sand bars in front of the mouths. Erosion coasts are distributed either between the river mouths (Hai Hau) or nearby them (Giao Long, Giao Phong, and Nghia Phuc). The evolvement of erosion is caused by wave-induced longshore southwestward sediment transport. Meanwhile sediment from the river mouths is not directed to deposit nearshore. The development of sand bars can intensively reduce the erosion rate nearby river mouths. Erosion in Hai Hau is accelerated by sea level rise and upstream dams. Sea dike stability is seriously threatened by erosion-induced lowering of beach profiles, sea level rise, typhoon, and storm surge.     

The first peak ground motion attenuation relationships for North of Vietnam

The first attenuation relationships of peak ground acceleration (PGA) and peak ground velocity (PGV) for northern Vietnam are obtained in this study. Ground motion data are collected by a portable broadband seismic network in northern Vietnam as a part of cooperation between the Institute of Geophysics, Vietnamese Academy of Science and Technology, Vietnam and Institute of Earth Sciences, Academia Sinica, Taiwan. The database comprises a total of 330 amplitude records by 14 broadband stations from 53 shallow earthquakes, which were occurred in and around northern Vietnam in the period between 01/2006 and 12/2009. These earthquakes are of local magnitudes between 1.6 and 4.6, focal depths less than 30 km, and epicentral distances less than 500 km. The new attenuation relationships for PGA and PGV are:

log₁₀(PGA)=-0.987+0.7521M_L-log₁₀(R)-0.00475R,     

Image smoothing of multispectral imagery based on the HNN and geo-statistics

A new method for image down-scaling using geostatistical interpolation or smoothing based on the Hopfi eld Neural Network (HNN) and zero semivariance value is introduced. The method utilises the smoothing effect of the semivariogram matching process to produce the smoothened sub-pixel multispectral (MS) image with smaller RMSEs in comparison with the bilinear interpolation. In fact, the zero semivariograms increase the spatial correlation between the adjacent sub-pixels of the superresolution image. Containing higher spatial correlation, the resulting super-resolution MS image has smaller RMSEs compared with the original coarse image.     

Freshwater stromatolites with the cone-in-cone structure from the Neogene lacustrine sediments of Vietnam

Morphological features of the columnar-stratiform stromatolites, which resemble the cone-in-cone structure, from Neogene lacustrine sediments of northern Vietnam are analyzed. Their structural-textural peculiarities and interrelations with the host terrigenous sediments of a stromatolitic buildup are discussed. It is shown that stages of the growth of columns are recorded in the succession of vertically oriented carbonate plates, which form stromatolites, and in the serrate surface protrusions of the plates at their contacts with host sediments. It is established that replacement of the columnar stromatolites by the stratiform varieties in the section can be related to variations in the intensity of terrigenous material influx to the sedimentation basin. Stratiform stromatolites were formed during relatively slow accumulation of sedimentary material. Appearance of the columnar varieties is attributed to intensification of sedimentation.     

Oligo-Miocene granitic magmatism in central Vietnam and implications for continental deformation in Indochina

Two granitoid intrusions within the Bu Khang extensional complex in central Vietnam have been dated by U–Pb and Rb–Sr geochronology. A monazite U–Pb age of 26.0 ± 0.2 (2σ) Myr was obtained for the Bu Khang pluton and 23.7 + 1.6/–1.7 Myr for monazite, allanite and zircon from the Dai Loc intrusion. These ages date crystallization of magmas previously assigned Precambrian to Devonian. Rb–Sr analyses of K-feldspar and biotite fractions from the samples yield ages of 19.8 ± 0.6 (2σ) Myr and 19.6 ± 0.5 Myr, respectively. The thermal history recorded by the different geochronometers implies an average exhumation rate of ∼2 mm yr⁻¹ corresponding to ∼9 km of unroofing. Magmatism was either (i) induced passively by lithospheric thinning driven by changes in regional tectonic stresses, or (ii) triggered actively by an ascending plume. Tertiary exhumation and magmatism documented elsewhere in Indochina (e.g. Ailao Shan-Red River and Wang Chao shear zones) favours a regional tectonic cause for extension and granitoid magmatism in the Bu Khang complex. On the other hand, the presence of an upwelling thermal anomaly since at least 35 Ma, causing mantle melting below Indochina, is supported by shear-wave velocity variations in the mantle, and source geochemistry of both the Bu Khang plutons and the Red River belt intrusions. In either case, Tertiary exhumation of the Bu Khang complex can account for previously undocumented NE–SW-directed extension, which is required in northern Vietnam to account for structural changes related to the opening of the South China Sea.