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.
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