Acta Geophysica

Biến đổi môi trường đã dẫn đến xung đột ngày càng gia tăng giữa cung và cầu nước ở sông Qinjiang. Bài báo này sử dụng dữ liệu về lượng mưa hàng tháng, dòng chảy, bốc hơi và nhiệt độ không khí trong khoảng thời gian từ 1956 đến 2016 và kết hợp phương pháp trung bình trượt 3 năm, hồi quy tuyến tính, kiểm định Mann–Kendall và phương pháp phân tích R/S để phân tích xu hướng biến đổi của từng yếu tố, kết hợp kiểm định Mann–Kendall, phương pháp bất thường tích lũy và kiểm định t trượt để phân tích biến đổi của từng yếu tố, đồng thời kết hợp phân tích sóng liên tục Morlet để xác định các dao động chu kỳ. Trong bài báo này, ảnh hưởng của biến đổi khí hậu và hoạt động của con người đối với dòng chảy của sông Qinjiang được đánh giá định tính từ các khía cạnh xu hướng, biến đổi và chu kỳ, và những đóng góp của biến đổi khí hậu và hoạt động của con người đến sự suy giảm dòng chảy được đánh giá định lượng bằng phương pháp chênh lệch bốc hơi và một phương pháp so sánh cải tiến về tỷ lệ thay đổi độ dốc của lượng tích lũy (SCRCQ). Các kết quả thu được như sau: (1) Từ năm 1956 đến 2016, lượng mưa cho thấy xu hướng tăng nhẹ, trong khi độ sâu dòng chảy và bốc hơi thể hiện xu hướng giảm đáng kể và nhiệt độ không khí cho thấy xu hướng tăng đáng kể. Lượng mưa và nhiệt độ không khí sẽ tiếp tục tăng, trong khi dòng chảy và bốc hơi sẽ tiếp tục giảm trong tương lai. (2) Lượng mưa không có biến đổi đáng kể, trong khi có hai điểm biến đổi (1986 và 2003) trong dòng chảy, ba điểm biến đổi (1974, 1986 và 2011) trong bốc hơi và một điểm biến đổi (1996) trong nhiệt độ không khí. (3) Đặc điểm của lượng mưa cho thấy sự tương đồng với các biến đổi chu kỳ của dòng chảy, trong khi lượng mưa thể hiện sự khác biệt đáng kể với bốc hơi và nhiệt độ không khí. (4) Hoạt động của con người đóng góp chủ yếu vào sự suy giảm dòng chảy. Đóng góp của hoạt động của con người vào suy giảm dòng chảy tăng từ 43,78% lên 61,17% trong giai đoạn BR (1983–2003) và tăng từ 61,17% lên 72,66% trong giai đoạn CR (2004–2016). Điều này cho thấy đóng góp của hoạt động của con người vào suy giảm dòng chảy đang tăng lên liên tục. Tác động của hoạt động của con người đối với sự suy giảm dòng chảy ở lưu vực sông Qinjiang chủ yếu là do sử dụng nước của các hoạt động tưới tiêu, công nghiệp và cư dân đô thị, điều này là do sự gia tăng dân số và tăng trưởng các chỉ số kinh tế.

The dual frequency SCINDA NovAtel GSV 4004B GPS receiver installed at the Ile-Ife (low-latitude station) has been in operation since December 2009. Data records for the year 2010 were processed to obtain Total Electron Content (TEC) and S 4 index. These were interpreted to analyze the ionospheric condition during low geomagnetic activity period (when Dst is from −40 to 0 nT) and during geomagnetic storm events (with Dst about −100 nT). Seasonal variations of the TEC and S 4 index were also investigated. The occurrence of scintillations is closely linked to the peak value of TEC during the daytime; this is very evident during the equinox months when TEC ≥ 30 TECu. When the maximum TEC value is below 30 TECu, as shown by most of the days in the summer months, the scintillation phenomenon does not occur. During geomagnetic storms, the daytime segment of the TEC plot experiences fluctuations (even bifurcations) in values with the peak TEC value of about 40 TECu. From the interpreted data, the occurrence of geomagnetic storm does not necessarily suggest an increase in the level of scintillations at a low-latitude region. Also, there is a remarkable difference between the IRI 2007 model and the observed TEC values, as the daytime TEC peak differs in magnitude and time of occurrence from the observed TEC.

Soft and hard interbedded rocks show obvious time-dependent deformation after deep tunnel excavations, and it is therefore necessary to research the mechanical behavior of the layered rock. However, it is hard to obtain ideal transversely isotropic rocks in fields, so rock-like specimens were poured by using artificial materials. Cyclic loading–unloading creep experiments were performed on the artificial layered cemented specimens with various layer angles (0°, 30°, 60° and 90°) at a 20 MPa confinement. Time-independent deformations and time-dependent deformations of the rock-like specimens were distinguished to investigate the visco-elasto-plastic deformation characteristics. Instantaneous elastic strain and instantaneous plastic strain had linear correlations with stress ratio, whereas creep strain, including visco-elastic strain and visco-plastic strain, increased nonlinearly with an increasing stress ratio. The specimens with a small layer angle had more noticeable time-independent and time-dependent deformations and larger steady-state creep rates than those of the specimens with a large layer angle. Attenuation creep and secondary creep could be observed at relative low stress levels, whereas accelerating creep until failure occurred at the creep failure stress level. The time for creep failure can be predicated according to the axial steady-state creep rate or volumetric creep curve. Damage in the rock-like specimens showed linear correlation with the stress ratio. Dip angle has a significant effect on the creep failure mode under cyclic loading–unloading conditions.

We apply a model-assisted technique to construct the topside electron density profile based on Digisonde measurements. This technique uses the Topside Sounder Model (TSM), which provides the plasma scale height, O+-H+ transition height, and their ratio Rt = H T /h T , derived from topside sounder data of Alouette and ISIS satellites. The Topside Sounder Model Profiler (TSMP) incorporates TSM and uses the model quantities as anchor points for the construction of topside density profiles. TSMP provides its model ratios with transition height and plasmaspheric scale height. The analysis carried out indicates that Digisonde derived F-region topside scale height Hm is systematically lower than one derived from topside sounder profiles. To construct topside profiles by using Hm, a correction factor of around 3 is needed to multiply the neutral scale height in the α-Chapman formula. It was found that the plasmaspheric scale height strongly depends on latitude and its ratio with the F-region scale height expresses large day-to-day variability.

In this study, an integrated approach has been adopted for optimum selection of locations for rain water harvesting (RWH) in Kohat district of Pakistan. Various thematic layers including runoff depth, land cover/land use, slope and drainage density have been incorporated as input to the analysis. Other biophysical criteria such as geological setup, soil texture and drainage streams characteristics were also taken into account. Drainage density and slope were derived from digital elevation model, and map of land use/land cover was prepared using supervised classification of multi-spectral Sentinel-2 images of the area. Aforementioned thematic layers are assigned respective weights of their importance and combined in GIS environment to form a RWH potential map of the region. The generated suitability map is classified into three potential zones: high, moderate and low suitability zones consisting of area 638 km2 (21%), 1859 km2 (62%) and 519 km2 (17%), respectively. The suitability map has been used to mark accumulation points on the down streams as potential spots of water storage. In addition, site suitability of artificial structures for RWH consisting of farm ponds, check dams and percolation tanks has also been assessed, showing 3.2%, 3% and 4.5% of the total area as a fit for each of the structure, respectively. The derived suitability will aid policy makers to easily determine potential sites for RWH structures to store water and tackle acute paucity of water in the area.

Cellular Automata have been used in the literature to describe seismicity. We first historically introduce Cellular Automata and provide some important definitions. Then we proceed to review the most important models, most of them being variations of the spring-block model proposed by Burridge and Knopoff, and describe the most important results obtained from them. We discuss the relation with criticality and also describe some models that try to reproduce real data.

The present paper aims at earthquake prediction assessment in Iran using VLF radio signal sounding and space-based ULF emission observation. VLF subionospheric data using the Denizkoy transmitter in Turkey at 26.7 kHz and a receiving station in Tehran are incorporated. Three earthquake events during 2019 located at different distances to the signal propagation path are used in this study. The short-term variations in the VLF signal for the 5 days averaged amplitude, as well as the deviation of the VLF signal against the 30 days averaged signal to monitor the alternation in the trend, are employed in this study to perform earthquake prediction assessment using VLF radio signal sounding. Several characteristic parameters of the VLF signal such fall-time, minimum 1 and minimum 2 throughout the day are used. A threshold over the standard deviation of the signal is used to determine the signal anomaly. The signal anomalies associated with three selected events and the correlation of prediction with the distance are discussed. A decision-making procedure for the detection of EQ-related anomalies based on the assessment of the proposed approach is introduced. The ULF emissions recorded by the China Seismo-Electromagnetic Satellite (CSES) are provided and associated with the two analyzed earthquakes using the VLF data due to lack of time coverage for the third case. The space-based detected ULF signals are presented and discussed. The proximity of the detected ULF emission with respect to the earthquake epicenter is discussed.

Sinuous channel flows are the most natural form of alluvial streams. The complex flow in the channel bends has been the main focus of the study. This paper examines the flow velocity and the three-dimensional velocity fluctuations in a pure sinuous channel. The main focus of the study is on the characterization of turbulence anisotropy along the sinuous bend. Experiments were conducted in a sinuous channel of a rectangular cross-section to identify the turbulence present in the flow. Secondary flow, Reynolds shear stress, turbulent kinetic energy, and anisotropy turbulence were evaluated in the sinuous bend. The bend apex is composed of a large circulation cell at the center of the bend section. The maximum Reynolds shear stress (RSS) is located at the bend apex with the streamwise-transverse and transverse-vertical components of RSS showing high peaks of positive and negative values. This fact is in support of the secondary flow observed in this study. Anisotropic stress tensors were estimated at different bend sections and are shown to have greater contribution toward streamwise and transverse direction. Anisotropic invariant map (AIM) identified the turbulence at bend sections and varying flow depth. Two-dimensional, cigar-shaped, and pancake-shaped turbulence was observed at the bend upstream and downstream. Isotropic turbulence was observed at the bend apex. Near the bed $$\left(z/h \le 0.2\right)$$ and away from the bed $$\left(z/h\ge 0.4\right)$$ , pancake-shaped and cigar-shaped turbulence was observed.

It is difficult to observe changes in the internal structure of natural rocks when under certain pressure ranges. However, such rocks have specific magnetic properties that are established during their formation process. Through studying changes in their magnetic properties while under pressure, which are readily observed and analyzed, as combined and contrasted with their associated structural changes, the relationship between the stress–strain and the magnetic field intensity can be established. Based on the stress–strain and magnetic field strength data obtained from the relevant literature, the process of rock and rock-like mechanical failure can be divided into three stages: elastic, plastic, and rupture. The performances of different rocks during these stages were analyzed, and there was an obvious transition point between any two adjacent stages. Thus, this study provides theoretical support to establish the relationship between structure and magnetic variations of rocks and rock-like bodies.