Evidences of Cenozoic strike-slip dislocations of the red river fault system in Paleozoic carbonate strata of Cat Ba Island (Northern Vietnam)

The structural researches of carbonate strata in the northeastern segment of the framework of the Red River Fault System (Cat Ba Island, Northern Vietnam) has been carried out. It was found that weakly deformed carbonate strata are cut by NW-trending (300–310°) strike-slip faults. Development of plicative and disjunctive dislocations occurred along predominantly sinistral strike-slip fault zones formed as a result of ENE regional compression (80°) during the Oligocene-Miocene phase of deformation. Late dislocations confined to the Pliocene-Quaternary phase of deformation (NNW regional compression 330–350°), are relatively less developed. Seismic monitoring data show that both plicative and disjunctive dislocations have continued to the present.     

Sandwaves on the Southeast Vietnam Shelf recorded by high resolution seismic profiles: formation and mechanism

The application of high resolution seismic data using boomer sound source has revealed a wide distribution of large-scale bedforms (sandwaves) on the Southeast Vietnam continental shelf. Bedforms that are a few meters high in wave height and hundreds of meters long in wavelength are primarily developed in the inner shelf (20–40 m) and considered to be formed under the present-day marine hydrodynamic conditions. Those bedforms developed in the deeper water (120 m) of the northernmost part of the continent can be interpreted as the relict morphological features formed during the latest sea-level lowstand of the late Pleistocene period. Two sediment transport paths have been identified on the basis of the bedform’s leeward orientation: northeast-southwest (along-shore) and north-south (cross-shore). A quantitative bottom current map is constructed from sandwave dimensions, surface sediments and measurement data. The strongest current velocities that gradually decrease toward the southwest are indicated by large sandwaves in the north (field B). Water depth, surficial sediment composition and bottom current are three factors that control the development of bedforms.     

Tectonic Activities and Evolution of the Red River Delta (North Viet Nam) in the Holocene

Geotectonics - The Red River delta with an area of about 12 620 km2 is one of the largest deltas of Viet Nam and it also is one of the remarkable deltas of Asia. The delta was formed during...     

Geoblocks Recognition and Delineation of the Earthquake Prone Areas in the Tuan Giao Area (Northwest Vietnam)

The goal of the paper is to reveal the hierarchical block structure in the Tuan Giao area (Northwest Vietnam) and, on that base, to identify areas prone to earthquakes with M ≥ 5. Four large geoblocks of the second rank have been delineated on the basis of the joint analysis of geological, geophysical, geomorphic, and remote sensing data. The second rank geoblocks have been divided into smaller sub-blocks of the third rank. The recent geodynamics of the geoblocks have been characterized using geomorphic, seismological, gravity, and GPS data.The system of the delineated geoblocks is viewed as the Geodynamic Blocks model. The areas prone to earthquakes with M ≥ 5 have been identified using the pattern recognition algorithm CORA-3. The objects of the recognition were defined as circular areas, where boundaries of the geoblocks intersect each other. The recognition results confirm high seismic potential of the study region and provide information on potential earthquake sources for seismic hazard assessment: a number of boundary intersections have been identified as areas prone to earthquakes with M ≥ 5, where events of such magnitude have not been recorded up to date. Mordern geothermal activity and anomalies of dissolved methane (up to 10000 nL/L), helium and hydrogen in the hot mineral water springs prove high permeability of the study area and its active seismo-tectonic state.     

Vertical fault systems in the tectonosphere geoelectrical section in petroliferous domains of Sakhalin Island (Russia) and Gulf of Tonkin (Vietnam): Evidence from magnetotelluric sounding

The transverse current anomalies evident from magnetotelluric sounding (MTS) data in the transition zone from the Asian continent to the Pacific Ocean and a geoelectrical model suitable for explaining these effects are discussed. Using simulation results and new MTS data on Sakhalin and northern Vietnam, ultra-deep fluid–fault system (UDFFS) models are constructed, comprising steeply dipping low-resistivity and high-resistivity linear bodies which penetrate through the whole section of the lithosphere, continuing deep into the asthenosphere. The structure of these systems reflects the development of deep and ultra-deep fault zones, along which mantle-originated fluids may migrate through sediments to reach the surface. This allows the anisotropic–conductive fractured structures adjacent to these faults to be considered as being most favorable for hydrocarbon accumulations.     

Land-Use Changes and Human Driving in and Near the Yangtze River Delta from 1995–2015

We analyzed the characteristics and trends of land-use change in and near the coastal zone of the Yangtze River Delta (YRD) during five periods (1995, 2000 2005, 2010, and 2015) using remotely sensed Landsat imagery. Using automatic supervised classification combined with visual interpretation, we obtained land-use information for five study areas (Nantong, Shanghai, Jiaxing, Ningbo, and Zhoushan). Significant land-use changes have occurred in this area between 1995 and 2015, characterized in particular by large reductions in cultivated land and rapid increases in urbanized land. In addition, land reclamation was very active in this period as an effective supplement to the increased demand for land development: since 1995, 1622 km² of land was reclaimed from near-coastal regions in the study area. This increase in urbanization was jointly driven by population, economic, transportation, and policy factors. Urban areas expanded from the center outward in concentric rings, with infrastructure guiding the radial expansion of development along transportation corridors, thus forming a network of connections. Due to the influence of national land regulation policies, the expansion rate of development in the YRD gradually diminished after 2010. This indicates that the area’s resource and environmental carrying capacity has reached a saturation stage in which urbanization has transitioned from broad and incremental expansion to the intensive use of land resources.     

Introduction to the China-Vietnam Cooperation Project: A Comparative Study of the Holocene Sedimentary Evolution of the Yangtze and Red River Deltas

Both China and Vietnam confront the challenges of natural geohazards and environmental changes in their deltas and coastal zones due to rapid urbanization, economic development, and the impacts of global climate change. China and Vietnam initiated a comparative study of the Holocene sedimentary evolution of the Yangtze River Delta(YRD) and Red River Delta(RRD) for the period 2015–2018 in order to improve the understanding of the two delta evolution histories in the Holocene. Previous investigative data of the two rivers, onshore delta plains, and offshore subaqueous deltas have been explored and reinterpreted. New data gleaned from boreholes, piston cores, shallow seismic and hydrodynamic sources have been collected from the offshore YRD and the East China Sea inner shelf, and surface sediments and short cores have been collected from the RRD near-shore areas. Six focal areas of the joint project have been defined for comparative studies of the two deltas, including morphological development, sequential stratigraphy, coastline shifting, sedimentary characteristics, sedimentary dynamics, and correlation with anthropogenic global climate change. The results of these study areas are presented herein. The joint project also includes cooperative capacity building; exchanges of young scientists have been organized during the project period, and hands-on training in laboratory geochemical analysis, numerical modeling, and seismic data processing and interpretation have been provided by China and its Vietnamese geoscientist partners. Joint field excursions were organized to the upstream of the Yangtze and Red Rivers in Yunan Province, China, all the way downstream along the Vietnamese portion of the Red River. These joint studies have, over the past three years, improved understanding of the evolutionary history of these two major rivers and their mechanisms of source to sink. Joint project results of these two major deltas are not limited to the geosciences; the cooperative mechanical and operational experiences have been helpful for future cooperation in the field of marine geoscience between China and Vietnam, as well for cooperative activities with other ASEAN member countries.     

Cretaceous Strike-Slip Dislocations in the Dalat Zone (Southeastern Vietnam)

Studies of ductile dislocations of the Jurassic terrigenous deposits and faulting kinematics of the Cretaceous injective structures in the Dalat zone show that the volcano-plutonic belt of southeastern Vietnam was formed under NE-striking sinistral dislocations affected by NNW transpression. This deformation took place in similar conditions as for the Cretaceous structure of the eastern margin of Asia. Due to the Indo-Eurasian collision, since the Cenozoic the Indo-Sinian Block has been displaced toward the southeast by a distance of more than 500 km from its primary position, causing transformation of the previously formed Cretaceous structures. Thus, the Cenozoic tectonogenesis in southeastern Vietnam should be studied with regard to the previous Cretaceous tectonic deformation.