In this paper, we present detail data of Pliocene - present tectonics and strain rate from GPS measurement and seismic interpretation. Using international reference frame ITRF08, we revealed absolute tectonic velocities of GPS sites with the slip rate to the east between 22 to 25 mm/year, to the south between 4 to 8 mm/year. The present strain rate was determined from present tectonic velocities that were consistent with the recent strain rates determined from seismic profiles, thickness of Pliocene - Quaternary sediments. Present day strain rate varying from 10 to 30 nano per year indicated that the region has been deformed weakly, in a stable tectonic regime.
The most important function of the coastal setback is to minimize damage due to coastal erosion, climate change response, and sea-level rise. There are many directions and methods of researching and assessing coastal changes and coastal erosion. This study presents the results of the shoreline changes in the area from Son Tra (Da Nang City) to Cua Dai (Hoi An City), Central Vietnam based on remote sensing data from 1965 to 2019. Three methods are used to include End Point Ratio (EPR), Linear Regression Rate (LRR), and Weighted Linear Regression (WLR). The results show that the EPR method is effective when calculating the rate of shoreline changes only at two different times. For more objective and reliable calculation, it is necessary to assess the shoreline changes over time. Meanwhile, the LRR method was shown to be superior because all shoreline data were taken into account during the construction of the regression line. However, when there is much shoreline data with different reliability, the WLR method proved more superior because of limited objective errors. The results show that from 1965 to 2019, the coast of the Son Tra - Cua Dai area had quite complicated fluctuations, of which the northern area (Son Tra) tended to accretion, the central area tends to be alternate between accretion and erosion, while the south area (Cua Dai) is strong to very strong erosion. The coast with sudden changes is the Cua Dai area with the shoreline change envelope (SCE) reaching 512m. The results also allow us to divide the coast of the Son Tra - Cua Dai area into 30 segments. They are clustered into 8 groups with different levels of erosion and accretion. This is an important basis for the setback zone establishment in the study area.
The estimation of the present day tectonic movement and tectonic gradient (strain rate) has an important practical signification in the assessment of active fault and seismic hazards for the selection of Ninh Thuan nuclear power plant. Based on the three campaigns of GPS measurement between 2012 -2013, we used BERNESE 5.0 software to determine present day slip rates of 13 stations in ITRF08 frame. The GPS stations move eastwards at the slip rates of 22 -25 mm/yr, southwards at the velocities of 5 -10 mm/yr. The standard errors in latitudinal and longitudinal directions are 1.2 mm/yr and 0.9 mm/yr, respectively. Combined with GPS data from the project of the study on actual geodynamics in Tay Nguyen TN3/06, we determined the strain rate ranging from 50 to 100 nanostrains with the standard error of 50 nanostrains. The direction of maximum compressive strain rate is from northwest -southeast to east -west.
The main objective of this paper is to investigate the mechanism of formation and evolution of a river mouth island in front of Cua Dai - a mouth of Vu Gia - Thu Bon river system. The combination of coastal morphodynamic analysis with remote sensing, mapping and GIS methods has shown that the formation and evolution of this island depends on a long-term and complex interaction between the dynamics of the Vu Gia - Thu Bon river system and the coastal littoral, including the Cu Lao Cham archipelago. This process has three stages: i) The formation of river mouth bar; ii) The formation of island in front of the river mouth; and iii) The deformation of island morphology in front of the river mouth. The materials that formed Cua Dai island are not only carried out by the Vu Gia - Thu Bon river system, but also from longshore sediment due to coastal and estuary erosion, mainly from the northern part of Cua Dai. Based on the interaction between material factors (river and longshore sediments) and energy (sea and river dynamics), the evolution of the river mouth bar in front of the Cua Dai island may follow one of two trends: i) The Cua Dai island will gradually move closer to the north shore of Cua Dai, erodes over time, then disappear, assuming no major flood in the Vu Gia - Thu Bon river system and wave and flow regimes are as normal as in the period before 2016; or ii) The Cua Dai island will continue to exist and change if there is an increase in climate change, especially extreme events such as storms, floods, and sea level rise.
Tạp chí Khoa học và Công nghệ biển T11 (2011
The main objective of this study is to assess geomorphic processes and active tectonics in the Day Nui Con Voi (DNCV) area of Vietnam. For this purpose, a spatial database was collected and constructed, including DEM (Digital Elevation Model) and a geological map. The hypsometric curve (HC) analysis method and its statistical moments were adopted to use for the assessment. These methods have been widely used for the assessment of geomorphic processes and active tectonics in many areas in the world showing promising results. A total of 44 sub-basins of the Red River and the Chay river were analyzed. The result shows that 3 curve-types such as "straight-shape", "Sshape", and concave were found; with the concave curve being the dominant and widely distributed in the northeast side and in the south of the southwestern side of the study area. The hypsometric integral (HI) values are rather small with the largest value is 0.37 and the smallest one is 0.128. Other statistical moments of the hypsometric curve, i.e. skew (SK), kurtosis (KUR), and the density function (density skew-DSK and density kurtosis-DKUR) show great values, which increased in the south direction of the area study. Accordingly, recent active tectonics (uplift-lower) in the study area is generally weak; however, they are also not completely homogeneous and can be distinguished by different levels. The southwestern side is being lifted higher than the northeastern side. The northern part is being lifted larger than the southern part. In the region, the uplift activities were increased gradually in the Pliocene-Quaternary and could have stopped at certain time in the past. The current geomorphic processes are mainly headward erosion in the upstream.
Chúng tôi ñã xác ñịnh chuyển dịch và tốc ñộ chuyển dịch tuyệt ñối của các ñiểm trong hệ toạ ñộ toàn cầu IGS05. Kết quả nhận ñược trạm LANG chuyển dịch về phía ðông với tốc ñộ ~39 mm/năm, chuyển dịch về phía Nam với tốc ñộ ~13 mm/năm. Tốc ñộ chuyển dịch của trạm BLV1 về phía ðông là ~29 mm/năm ñồng thời chuyển dịch về phía Nam với tốc ñộ ~14 mm/năm. Trạm STT1 chuyển dịch về phía ðông với tốc ñộ ~22,5 mm/năm và chuyển dịch về phía Nam với tốc ñộ ~10,5 mm/năm. Tốc ñộ chuyển dịch về phía ðông của trạm CDA1 ~21 mm/năm và chuyển dịch về phía Nam ~10 mm/năm. Tốc ñộ chuyển dịch về phía ðông của trạm DOHO là ~26,8 mm/năm và chuyển dịch về phía Nam là ~9 mm/năm. Tốc ñộ chuyển dịch về phía ðông của trạm HUES ~30 mm/năm và chuyển dịch theo hướng Nam ~20mm/năm. Tốc ñộ chuyển dịch về phía ðông của trạm HOCM ~21,5 mm/năm và chuyển dịch theo hướng Nam ~12mm/năm. I. MỞ ðẦU Biển ðông ñược xem là biển rìa thuộc vành ñai Tây Thái Bình Dương. Rìa ðông
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