Journal of Asian Earth Sciences: X最新文献

Coal mining is critical to the functioning of the current Afghan economy providing jobs, tax revenue, and foreign exchange. Taxes on coal may constitute the Taliban Government’s single largest source of operating income. Prior to the start of mining, Afghanistan had between 215 M and 430 M tonnes of hypothetical category Jurassic coal resources at depths accessible to artisanal miners. Since 1940, between 51 M and 89 M tonnes of coal have been extracted. Technologically primitive mining practices result in suboptimal coal extraction from disorganized room and pillar mines leaving significant amounts of coal unmineable. Frequent tunnel collapse, gas and coal dust explosions, and uncontrolled widespread mine fires have destroyed or made inaccessible significant additional volumes of remaining artisanally mineable resources. The haphazard unmapped development of the existing Jurassic coal makes it impossible to redevelop these fields using more efficient mining technologies. If new mines are to be developed, they will have to tap subsurface coals not accessible to artisanal miners. 66 % of the area mapped as Lower to Middle Jurassic rock does not host outcropping coal beds. This area, as well as some of the areas beneath thin veneers of lowest Cretaceous sediment are potential exploration targets. Jurassic coals are very gassy. Developing coalbed methane prospects is a more effective and less environmentally destructive means to access the energy contained in the Jurassic coals.

This study presents the results of shuttle radar topography-based analysis providing new insights into the geological and structural architecture of the island of Borneo. The aim is to examine whether Borneo is tectonically active and to better understand the origin of prominent topographic features such as the Dulit Plateau and the large oroclinal bend of Sarawak. The results show that the Tinjar and the Lupar lines are tectonically active fault zones. The Lupar fault zone is broadly distributed along the spine of the island, representing a major suture featured by ophiolites and extensive volcanism. The development of the Dulit Triangle and the large oroclinal bend are related to fault interactions. The seismological, geodetic and geomorphological evidence suggests that Borneo is tectonically active. The Borneo Island Fault is the major active fault piercing through the island’s mountainous backbone. On a tectonic scale, the oblique northeastward active convergence of the Australian plate with the Sunda plate drives the deformation on the island of Borneo, some of which is also associated with the northward motion of the Philippine Sea plate. Recent GPS data indicate that the Sunda plate is moving slowly to the southwest, and our results suggest this motion is consistent with the interaction between the Sunda and the Australian plates.

The Red River originating from Yunnan province, China is the second largest river in Vietnam in terms of length and discharge. Combination of water chemistry monitoring data of 4 years (2018–2022) from different sub-basins of the Red River (the Da, Lo, Thao, Tra Ly, and Day) with historical datasets indicates a decline in pH from 8.1 in 2000 to 7.7 in 2021, greater CO₂ concentrations and a shift from waters naturally dominated by carbonate weathering to waters dominated by evaporite weathering. Such changes were most apparent in the delta area where heavy human activities have increased influxes of most dissolved chemicals, except SiO₂. Evaporite weathering is particularly enhanced by mining and deforestation occurring in upstream regions of both China and Vietnam. Pyrite oxidation, alongside silicate weathering, is enhanced along the Red River Fault Zone but reduced in tributaries with a higher proportion of hydropower reservoirs. Longer water residence times in these large reservoirs (total volume > 2.7x10¹⁰ m³) located in the Da and Lo sub-basins have also increased primary productivity, leading to higher evasion/uptake of CO₂ and SiO₂, lower total dissolved solids (TDS), and higher pH. The total physical and chemical denudation rates of upstream mountain tributaries ranged between 0.107 ± 0.108 and 0.139 ± 0.137 mm yr⁻¹, mainly due to reservoir implementation and instream aquatic biogeochemistry changes. Our findings demonstrate that anthropogenic activities are profound factors impacting the water chemistry of the Red River system.

The Meishan-Chiayi area of western Taiwan has a large probability of producing a major earthquake in the near future. Historically, one of the largest and most damaging of Taiwan’s earthquakes occurred there. It is, therefore, important to have a well-constrained upper crustal 3-D shear-wave velocity model that can be used to accurately determine ground motion predictions and fault geometry models used in seismic hazard and risk modelling. In this study, we carried out an ambient noise tomography experiment using 100 seismometers deployed with a ∼2 km spacing on a 20 by 20 km grid. The reliable periods of phase velocity from Rayleigh waves are 0.6 to 6.8 s, providing a well-resolved Vs structure from the surface to a depth of around 4 km. The velocity model displays a prominent, roughly northeast-striking change in Vs that follows the projected surface trace of the blind Chiayi thrust. The uplift of relatively higher Vs rocks in its hanging wall, together with a negative to positive change in dVs suggests that it dips gently eastward across the study area. A northward thickening of the lower Vs crust, together with a high negative dVs in the north of the study area is related to an increased thickness of foreland basin rocks across the Meishan fault. The Vs and dVs models provide reasonable evidence that the Meishan fault can be traced at a high angle from its surface rupture to the base of the model at 4 km depth. It cuts the Chiayi thrust.