Vietnam Journal of Earth Sciences

The paper presents a fundamental theory of the H/V ratio technique (or Nakamura’s method) and several obtained results in Hanoi by using this method. This is one of the most inexpensive and convenient technique to reliably estimate the fundamental resonance frequencies of soft deposits. However, the ability of the method in estimating site amplification on surface’s ground motion still remains as an open question and deserves more work to elucidate. Herein, we investigate aspects of the method at sites in Hanoi city by comparing observed H/V ratios with corresponding theoretical transfer-functions. The main goal of the study is to investigate the applicable sides of the H/V ratio method in Vietnam, and for geological conditions of Hanoi city, the H/V ratio method is a good choice for the site effect estimations.

This paper presents the Directional Derivative method to determine location and boundaries of the magnetic directional structure sources through a new function DG (Directional Gradient - DG). Algorithm and computer program are made a code by Matlab language to attempt to calculate on 3D models in the compare with Horizontal derivative method (HG). A new function DG also applied to determine the boundary of magnetic sources by the total magnetic anomalies of Tuan Giao region. The result shows that with the application of new function DG, the boundaries of magnetic sources are exactly defined although they have a directional structure and small horizontal size. Moreover, because it does not depend on directions of magnetization, so in the computation, the transformation of the magnetic field to the pole can ignore, thus, reduce transient error. Alternatively, with the application of new function DG, the interferences in case the sources distributed close together are overcome. This usefulness affirms the possibility of application of the this method in the analysis and interpretation of magnetic data in Vietnam.ReferencesBhaskara Rao D. and N. Ramesh Babu, 1993. A fortran 77 computer program for tree dimensional inversion of magnetic anomalies resulting from multiple prismatic bodies, Computer & Geosciences, 19(8), 781-801.Beiki M., David A. Clark, James R. Austin, and Clive A. Foss, 2012. Estimating source location using normalized magnetic source strength calculated from magnetic gradient tensor data. Geophysics, 77(6), J23-J37. Blakely R.J., and R. W. Simpson, 1986. Approximating edges of source bodies from magnetic or gravity anomalies: Geophysics, 51, 1494 -1498. Blakely R.J., 1995. Potential theory in gravity and magnetic applications, Cambridge University Press. Cao Dinh Trieu, Pham Huy Long, 2002. Tectonic fault in Vietnam. Publisher of Science and Engineering. Debeglia N. and J. Corpel, 1997. Automatic 3-D interpretation of potential field data using analytic signal derivatives. Geophysics, 62, 87-96.Geological and Mineral resources map on 1:200,000. Seriesof Tay Bac, sheets of Muong Kha - Son La (F-48-XXV-F-48-XXVI), Phong Sa Ly - Dien Bien Phu (F-48-XIX-F-48-XX), Kim Binh - Lao Cai (F-48-VIII-F-48-XIV), 2005. Published and copyringt by Department of Geology and Minerals of Vietnam, Hanoi. Le Huy Minh, Luu Viet Hung, Cao Dinh Trieu, 2001. Some modern methods of the interpretation aeromagnetic data applied for Tuan Giao region. Vietnam Journal of Earth Sciences, 22(3), 207-216. Le Huy Minh, Luu Viet Hung, Cao Dinh Trieu, 2002. Using the maximum horizontal gradient vector to interpret magnetic and gravity data in Vietnam. Vietnam Journal of Earth Sciences, 24(1), 67-80. Nabighian M.N., 1972. The analytic signal of two-dimensional magnetic bodies with polygonal cross-section: Its properties and use of automated anomaly interpretation: Geophysics, 37, 507-517. Nabighian M.N., 1974. Additional comments on the analytic signal of two-dimensionalmagnetic bodies with polygonal cross-section. Geophysics, 39, 85-92. Roest W. R., J. Verhoef and  M. Pilkington, 1992. Magnetic interpretation using the 3-D analytic signal: Geophysics, 57, 116-125. Vo Thanh Son, Le Huy Minh, Luu Viet Hung, 2005. Three-dimensional analytic signal method and its application in interpretation of aeromagnetic anomaly maps in the Tuan Giao region. Proceedings of the 4th geophysical scientific and technical conference of Vietnam, Publisher of Science and Engineering 2005. Vo Thanh Son, Le Huy Minh, Luu Viet Hung, 2005. Determining the horizontal position and depth of the density discontinuties in Red River Delta by using the vertical derivative and Euler deconvolution for the gravity anomaly data, Journal of Geology, Series A, 287(3-4), 39-52.Vo Thanh Son, et al., 2007. Determining the location and depth of contrast magnetic boundaries by using 3D analytics signal method and higher derivatives. Proceeding of the 5th geophysical scientific and technical conference of Vietnam. 

About the history of relief development of coastal islands in Vietnam

Recent tectonics of Red River fault zoneand adjacent

summaryCenozoic stratigraphy of the coastal plains inthe South Central VietnamBy reviewing present stratigraphical divisions in the South Central Vietnam, the authors have given some following proposals :The Song Ba formation is dated of Middle - Late Miocene age ; both Di Linh and Kon Tum formations of Late Miocene - Early Pliocene age; the Mavieck one of Late Miocene - undivided Pliocene age andPhan Thiet of Middle - Late Pleistocene age were formed in marine condition. The Nha Trang formation, dated of Early - MiddleHolocene age with alluvio-marine genesis, should not be used because this name was previously published for another Cretaceous formation.The second river-terrace sediments, Song Luy Basalt of Late Pleistocene age and the Song Luy Formation of Pliocene age should be continued to study in their relationship.The proposed Cenozoic stratigraphical scale for the South Central coastal Plains of Vietnam is compo-sed of 14 divisions, of which, 4 for Neogene and 14 for Quaternary.

Seismic Risk Assessment for Mega-cities in VietnamEarthquake threats usually appear in high seismicity areas and become particularly dangerous if those areas at the same time are urban ones. Planning and investment for strategies on mitigation of losses and damages due to earthquake and tsunami now become an urgent issue for many countries in the World. Moreover, these strategies have to be made and implemented while earthquake or tsunami did not happen in order to avoid much more expenses for the during disaster rescue activities, or for the after disaster restore and recovery activities.Starting from the year 2000, many researches on urban seismic risk assessment have been implemented in Vietnam. The typical seismic risk assessment problem essentially lies in the modeling of earthquake sources and development of realistic earthquake scenarios, which serves as a basis for the estimation of earthquake - related damages and losses in urban areas. A methodology suitable for Vietnam was developed and applied for several megacities of Vietnam. The application of GIS technology allows developing a powerful tool for implementation of quantitatively risk evaluation procedure for an urban area and display results in terms of maps showing building damage and casualties at different levels and at different times of a day.This paper presents some preliminary results of using GIS to assess seismic risk and to estimate losses for urban areas of three biggest cities in Vietnam, namely Hanoi, Ho Chi Minh City and Nha Trang. Although the methodology has been applied to alimited framework, the obtained results show a realistic picture of damage and loss that may result from future earthquakes aturban scale. The estimates of damage and human impacts due to earthquakes can help the decision-makers at local, regionaland national levels in:1. Mitigating the possible consequences of earthquakes;2. Anticipating the possible nature and scope of the emergency response needed to cope with an earthquake/tsunamirelateddisaster, and3. Developing plans for recovery and reconstruction following such a disaster.

The allocation of foreshocks and aftershocks from earthquake catalog of Southeast Asia (period 1278- 2008) by method "space-time window" ...

Bien Ho is one of the volcanic landscapes showing lava eruptions that occurred millions of years ago. It is a symbol of the volcanic landscapes in the Tay Nguyen, Vietnam, which keeps a lot of values. This article aimed to quantify recreational and conservative values. The travel cost and contingent valuation method were used to estimate the recreational and conservative value (existence, bequest, and option value) of Bien Ho, respectively. The results indicated that the recreational and conservative value of Bien Ho volcanic landscape was 1,436.9 billion VND and 38.6 billion VND, respectively. The average willingness to pay in the contingent valuation method was 39,388 VND and depended only on ethnicity and age. The study used different populations to define survey samples according to each estimating method to improve the confident accuracy of the results.

Seismic Hazard assessment of the South Vietnam and Ho Chi Minh City region ...

The main objective of the present study is to apply Artificial Neural Network (ANN), which is one of the most popular machine learning models, to accurately predict the soil unconfined compressive strength (qu) for the use in designing of foundations of civil engineering structures. For the development of model, data of 118 soil samples were collected from Long Phu 1 power plant project, Soc Trang Province, Vietnam. The database of physicomechanical properties of soils was prepared for the model study, where 70% data was used for the training and 30% for the testing of the model. Standard statistical indices, namely Root Mean Squared Error (RMSE) and Pearson Correlation Coefficient (R) were used in the validation of the model’s performance. In addition, Partial Dependence Plots (PDP) was used to evaluate the importance of the input variables used for modeling. Results showed that the ANN model performed well for the prediction of the qu (RMSE = 0.442 and R = 0.861). The PDP analysis showed that the liquid limit is the most important input factor for modeling of the qu. The present study demonstrated that the ANN is a promising tool that can be used for quick and accurate prediction of the qu, which can be used in designing the civil engineering structures like bridges, buildings, and powerhouses.