مجله ژئوفیزیک ایران
سال هفدهم شماره 3 (پیاپی 60، Autumn 2023)

For extended structure, the seismic load has a spatiotemporal variation that simultaneously changes with time and space. The incorporation of the seismic wave spatial random variability effect is especially important when large structures such as long bridges, dams, and large buildings are analyzed. The effect of spatially varying earthquake ground motion (SVEGM) on the seismic response of earth dams is analyzed in this paper. To this end, a parametric study is conducted to investigate the effects of length to height ratio ( ) on the 3D seismic response of the studied dams. Ground motions, consistent with the three-directional lagged coherency model, are generated at different discretized cells at the base of the dam. The dams are assumed to sit on trapezoidal and V-shaped canyons and vibrate in all three directions, upstream-downstream, vertical, and longitudinal. The average coherency of different frequencies is calculated and used for the generation of SVEGM. The time histories are simulated using a spectral representation-based method. The separation distance between the cells is determined in such a way that 90% of correlation between seismic input motions can be captured. For each case of  ratio, a numerical model of the dam and its foundation is constructed using the finite difference numerical method. The 3D seismic behavior of the earth dams is evaluated under the artificially generated three-directional components of SVEGM. Generally, it is concluded that with increasing  ratio, at the midpoint of the dam crest, the difference between maximum of acceleration values obtained by applying uniform and SVEGM excitations decreases. In all cases of analyses, SVEGM has decreasing effect on the vertical displacement of dam crest.

This paper represents the analysis and interpretation of the airborne magnetic data of central and northern Egypt to delineate the subsurface faults and other structures and also the tectonic framework of the area. First, the total observed magnetic field data was reduced to the north magnetic pole (RTP) and using the power spectrum, the regional and residual magnetic fields were separated using the Butterworth filter to isolate the anomalies caused by each of them. Then, the airborne magnetic data was subjected to several filters to enhance the signals from the different magnetic sources for better delineation and edge detection. Additionally, Euler deconvolution was applied to estimate the depth of the different magnetic sources.The final outputs show a wide variety of magnetic anomalies reflecting different magnetic sources and subsurface features. The main subsurface structures are the linear NNW-SSE parallel to the Red Sea trend and the Gulf of Suez and the NE-SW faults and lineaments surrounding the basins in the northern and western area, the deeply rooted basic intrusions, and the depo-centers (basins) in the western and central parts of the area. Moreover, the area shows several basement uplifts and consequently faulted basins of different directions and displacements.

This paper represents the analysis and interpretation of the airborne magnetic data of central and northern Egypt to delineate the subsurface faults and other structures and also the tectonic framework of the area. First, the total observed magnetic field data was reduced to the north magnetic pole (RTP) and using the power spectrum, the regional and residual magnetic fields were separated using the Butterworth filter to isolate the anomalies caused by each of them. Then, the airborne magnetic data was subjected to several filters to enhance the signals from the different magnetic sources for better delineation and edge detection. Additionally, Euler deconvolution was applied to estimate the depth of the different magnetic sources. The final outputs show a wide variety of magnetic anomalies reflecting different magnetic sources and subsurface features. The main subsurface structures are the linear NNW-SSE parallel to the Red Sea trend and the Gulf of Suez and the NE-SW faults and lineaments surrounding the basins in the northern and western area, the deeply rooted basic intrusions, and the depo-centers (basins) in the western and central parts of the area. Moreover, the area shows several basement uplifts and consequently faulted basins of different directions and displacements.

Shallow Water Flow (SWF) is a type of geohazard in hydrocarbon exploration in deep-water basins. This problem occurs in deep-water basins with high sedimentation rates. When the drill hits overpressured layers below the seabed, large volumes of water and sand flow along the wellbore and ultimately, loss of well integrity may occur. This is the first study to review the literature on predicting SWF predrilling from different aspects comprehensively. We also evaluate the SWF problem in the channel by using 3D seismic data in the South Caspian Basin (SCB) as an example of a deep-water basin prone to SWF geohazard. The results of the literature show that geological settings with rapid subsidence are more likely to be associated with SWF. Pleistocene low-stand sands, channels, slumps, and chaotic zones are more prone to SWF. Compaction disequilibrium, differential compaction, and hyperpressure are the mechanisms of SWF. The most important quantitative criteria for identifying SWF environments are Vp/Vs and Poisson's ratios, P-impedance (AI), and S-impedance (SI). Post-stack and pre-stack inversion, seismic stratigraphy, seismic attributes, and geopressure prediction are the most important techniques for evaluating SWF. The results of post-stack inversion including low impedance zones and AI<3150 ((m/s).(g/cc)), show SWF problem in the central and eastern parts of the buried channel in the SCB. The review findings provide a comprehensive understanding of SWF geohazard in deep-water basins. As recommended in this review, further review research should be done to stabilize shallow water flow zone during the drilling operation.

In this study, advanced means in remote sensing techniques and Digital Elevation Models (DEMs) computed from modern satellite images of the studied area were used as raw data by a program for measuring spatial and geographical analysis.     Results of morphometric analyses are based on field data analysis and manually drawn watershed boundaries. Results from GIS depend on how accurate the DEM data utilized it after eliminating all no-data voids and filling in sink holes in the raw DEM data for the study area. It was discovered that SRTM-DEM with a reasonable resolution of 30 meters per grid cell provided accurate delineation for the surrounding topographic area of Hadetha Dam Lake in morphometric analysis. The hydrogeological study indicated that there are five underground basins: the modern sedimentation basin, the Injana basin, the Fattah basin, the Euphrates basin and the Umm Al-Raduma basin. There are also basins within the water formation in Injana and the Euphrates. The basin area and circumference were measured using the GIS Arc View geographic information system. The area and the circumference of the basin were 166 Km2 and 244 Km, respectively. The soil permeability ratio of the main basin is high and rainfall is low. Therefore, the area is characterized by the presence of large and karst caves and cracks spread, thus creating a good area for the process of filtering rainwater into the ground to feed the layers that have the ability to collect water, and forming layers that contain groundwater.

Visibility deterioration may have negative impacts on aviation safety, particularly in landing and take-off procedures. Beside traditional weather observation methods which are based on human visual estimations, automatic weather observation systems (AWOS) are recently used in airports in order to provide instant measurements of the relevant meteorological parameters. One of the most important sensors is the RVR sensor. In this study, the variability of human visibility and optical instrumental visibility, including the meteorological optical range (MOR) and runway visual range (RVR), along with the probable differences between their values are investigated from December 2019 to February 2020 at Payam Airport, Karaj, Iran.    Results indicate that in different weather conditions, the values of MOR and RVR are predominantly greater than human visibility. In this investigation, MOR is about 99% and 96% more than observed visibility for daytime and nighttime, respectively. The probable reasons for such discrepancies between these two sources of data have argued in this paper. However, to overcome the differences between the two methods, an optimized parameter is introduced as visual optical range (VOR). This parameter simulates human’s visibility through MOR to gain the benefits of both methods. Using darkness coefficient, the new parameter depends not only on extinction coefficient but also on sky brightness. The value of 0.07 is proposed for VOR calculation instead of 0.05 in the calculation of MOR. Meanwhile, in the new method, RVR value is also taking the greater values of the Allard’s visibility and VOR rather than MOR. Applying this method, it is observed that VOR values align between traditional and instrumental visual ranges. Furthermore, the new method gives more reasonable results considering minimum values of the runway’s light intensity over nighttime.

Aeromagnetic and core drilled data covering parts of southern Nupe Basin was acquired and interpreted with the view of evaluating the mineral potential of the area through interpretation of the structural features in the area, determination of the Curie isotherm depth, and correlation of aeromagnetic outcomes with the core sample data from the area. Two major regional fault trends were interpreted: northeast–southwest (NE–SW) and NNE–SSW with minor northwest–southeast (NW–SE) directions. Two depth sources in the area are delineated, namely zone of shallow seated basement which ranges from 0.42 km to 1.5 km and zone of deeply seated basement ranging from 1.91 to 3.50 km. Results of qualitative interpretation of the total magnetic intensity map (TMI) and residual intensity map reveal that the magnetic intensities range from 7500 to 8460 nano-Tesla (nT) and -220 to 240 nT, respectively. The depths to the centroid and top of the magnetic causative bodies range from 9.00 to 17.10 km and 0.4 to 3.10 km, respectively. There are evidences of oolitic iron ore in some parts of the study area. Juxtaposing the topographical and core drilling data reveal that the oolitic iron ore level follows the topographical level which implies that the topography of the area controls the configuration of the iron ore deposit level. All these deductions are made considering the geology of the area.