Vietnam Journal of Earth Sciences

Algorithm using GIS for Earthquake RiskAssessment for Vietnam

At approximately 5:00 AM on December 16, 2016, a rapid and deep-seated landslide was triggered by intense rainfall in the Van Hoi irrigation reservoir in Binh Dinh province, Vietnam. The landslide generated an impulsive wave with a height of approximately 20 m, resulting in severe damage to the reservoir operation station. This study investigated the mechanisms behind the landslide's initiation and simulated its initiation and motion processes through site surveys, ring shear tests, and the LS-RAPID simulation model. The physical tests were conducted on two soil samples from the sliding zone to examine the landslide mechanism. The results indicated that only sample 2 (a sand sample of completely weathered gneiss rock) showed a high level of landslide mobility due to its liquefaction phenomena resulting in a rapid pore water pressure development and a significant strength loss. In contrast, sample 1 (a silty sand sample of residual soils) did not exhibit this behavior due to its high shear resistance value at a steady state. The findings suggest that the sliding plane of the Van Hoi landslide formed in the completely weathered gneiss layer, and the high mobility level of sample 2 is primarily responsible for its rapid movement. Notably, the LS-RAPID model successfully reproduced the landslide process using the geotechnical properties obtained in the ring shear experiments. The simulation showed that the Van Hoi deep-seated landslide was initiated from the lower middle slope at a critical value of 0.55 for the pore water pressure ratio and traveled at a high velocity of approximately 37.0 m/s. The consistency between the computer simulation results and the on-site evidence and recorded data highlights the reliability of the LS-RAPID model as a tool for assessing landslide hazards.

Currently, Manganese (Mn) pollution in groundwater in Ho Chi Minh City was detected and became an interested issue for many researchers. In a well which belongs to the water supply company in HCM city, Mn contents comparing to standards increase many times and fluctuate by seasons markedly, while in some other wells, the Mn contents are still relatively stable. The content of Mn, similar to that of As, has a close relationship to iron content in the water. The correlation coefficient between iron and manganese reached 0.99856, showing that they have a syngenetic relationship.From some results of data processing on the concentration of Mn2+ and Fetc, it is stated that: the content of Mn2+ cannot be derived from the surface waste seeping down because it is minimum in the shallowest aquifer qp2-3. The concentration of Mn2+ ions increases in tandem with the depth. Their origin in groundwater related to the origin and composition of sediments of aquifer and aquiclude. The infiltration mechanism of Mn into the water is not clear. The treatment of Mn in groundwater is proposed in the paper, but other cheap solutions in accordance with the conditions of the community still need to find.

Bioclimatic conditions in some sanatorium areas of Northern mountainuos part of Vietnam

Mafic and ultra mafic formations in ophiolite archs of Vietnam

The Eastern California earthquake (also known as the Ridgecrest earthquake) occurred at 03:19:53 (UTC) on the 6th of July, with a moment magnitude of 7.1. Over the region, there is an accurate network of GNSS permanent stations. Precise determination of displacements of these stations will provide important information to better understand the structure and scope of the earthquake, contributing to faster and more accurate earthquake prediction. In this paper, we used precise point positioning with ambiguity resolution to determine the co-seismic displacements of 25 GNSS stations around the epicenter for the day of the earthquake. The processing results show that the affected area being more than 100 km centered around the earthquake epicenter with the largest value being approximately 0.6 m.

At present, most of produced petroleum fields have reserve dozens of million tons of oil, dozens of billion m3 of gas. To design production, these fields must be seriously and carefully evaluated in terms of economics and geology aspects, otherwise risks will be high. With fields have reserve up to 10 million tons of oil, 10 billion m3 of gas, which are considered small fields , are not or a litter economic effective when production. These discoveries are usually returned to the state from contractors. There fore, producing petroleum small fields effectively is sensitive matter, is attention of many countries, but it is not easy. Making necessary regulars to develop petroleum small fields production has important meaning to economy. 

Until now, the structures of the earth’s crust in the area of Song Tranh and it’s adjacents are only reflected sketchy in the studies of regional characteristics, mostly in the structural schemes established for whole country. Since the year 2012 in the area of Bac Tra My district, Quang Nam province are appeared a series of earthquakes after an water filling of the hydroelectric power plant reservoir Song Tranh 2. A portion of the events are produced the ground motion of threat level for local peoples. The numbers of houses are subjected to damage. The increase suprisingly of the seismic activity in that area is recongnized as an induced earthquake phenomenon by most of scientists worked in this research direction. Understanding the mechanism of earthquake occurence and earthquake hazard level are important. The different types of data are needed for the research, including a more detail scheme of crustal structures. Since the available data capable for study of the earth’s crust in that region are only the garvity and magnetic amomaly maps of scale 1:500 000 and 1: 200 000 respectively. Since the garvity anomalies are demonstrated a good correlation not only with the regional geotectonic environment obtained in the previous studies but also with the local structural elements, it’s extraction using a more dense network of profiles is expected to generate a more detail scheme of crustal structutes in the region. Thus, 8 profiles with the distance from one to another varried in a range 12 - 16km were designed for the study area resticted by the latitudes 15°N and 16°N. The 2.5D gravity modelling is applied for data interpretation. The initial model for each profile was constructed by using all the available data related to the structures. The calculations were perfomanced by iterative process. The target function indicated an average square deviation between the theoretical and observed gravity data along each profile is calculated for each iteration. To minimize the target function, the least - squares method is used and the model parameters were changed by using both the Marquardt’s algorithm and interpreter - computer interaction. The calculation process terminated when the target function is became small enough and the respective density model is accepted as the reasonable structural cross sections. The target function <1.0 is accepted as a threshold to terminate the iterative calculated process in this study. In fact, it’s values varried from 0.657 to 0.994 are obtained in the calculations for 8 profiles. Combine all the density models derived from the calculations, the more detail schemes of the Moho, Conrad and Crystaline surfaces were constructed. A series of local structural elements appeared on its are demonstrated as a new information in comparison with the previous regional studies. In addition, the uprising tendency of the Crystaline basement from East to West derived from the previous studies is replaced by the subsidence with the depth reached more than 5km in the area closed to Viet - Lao border.ReferencesTrịnh Việt Bắc, Đinh Văn Toàn, 1996: Một số kết quả nghiên cứu cấu trúc địa chất sâu lãnh thổ miền Bắc Việt Nam bằng phương pháp giải bài toán ngược trọng lực 2,5 chiều. Nxb. KHKT. Địa chất tài nguyên, V1, 206-215. Bản đồ Địa chất và khoáng sản Việt Nam tỷ lệ 1: 1.000.000. Cục Địa chất và Khoáng sản Việt Nam xuất bản 2004. Lưu trữ Địa chất. Bulax E. G., V. A. Pjanisun, M. N. Markova, 1976: Áp dụng phương pháp cực tiểu hoá hàm số để giải bài toán cấu trúc địa chất theo tài liệu trọng lực. Nxb. Nauka Dumka, Kiev 1976 , 218 tr (tiếng Nga). 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The characteristics of active faults and the erosion hazard at the South Central Vietnam coast