Contributions to Geophysics and Geodesy

On possibilities of improving the accuracy of the geocentric gravitational constant GM by combining SLR and atomic clocks measurements

2025-03-30T15:13:48+00:00

Nowadays, the geocentric gravitational constant GM is determined by solving equations of motion for trajectories of artificial satellites measured by Satellite Laser Ranging (SLR). The estimated value of GM and its uncertainty 398600441.8 ± 0.8×10⁶ m³s⁻² are currently adopted by the International Astronomical Union. In this study, we investigate possibility of improving the accuracy of GM by integrating atomic clocks measurements with SLR. The functional model defines GM in terms of geopotential differences observed by atomic clocks at two points in space and their distance measured by SLR. Two types of observation equations are established. The first equation defines geopotential differences with respect to the geoidal geopotential value W₀. The second equation defines distances with respect to the geocentric position of ground-based station determined from GNSS measurements. With the improving stability of atomic clocks to 10⁻¹⁸, it will be possible to measure geopotential differences with the accuracy ±0.1 m²s⁻² (equivalent to ±1 cm in terms of the geoidal heights), while SLR measurements can currently be carried out with sub-centimetre accuracy under optimal conditions and applying advanced corrections and numerical procedures. Taking into consideration both, accuracy characteristics and their expected improvement, we conduct sensitivity analysis to assess accuracy requirements needed to improve the accuracy GM (±0.8×10⁶ m³s⁻²). Error analysis indicates that combination of relativistic measurements with SLR cannot improve the accuracy of GM due to insufficient stability of atomic clocks. Nevertheless, the accuracy improvement by an order of magnitude might be feasible if relativistic measurements are carried out by atomic clocks with stability 10⁻²⁰ (or better), while also achieving sub-millimetre accuracy of SLR. Integration of relativistic measurements with SLR could improve the accuracy of GM, while the critical aspect is determination of the geoidal geopotential value W₀ with sub-millimetre accuracy in terms of geoidal heights that could be achievable.

Spectral gamma-ray and conventional logs to evaluate hydrocarbon potentiality in Bahareya Formation, Hayat oil field, Northwestern Desert, Egypt

2025-03-29T13:48:58+00:00

Different reservoir parameters (volume of shale, total and effective porosities, water saturation and hydrocarbon saturation) of Bahareya Formation were calculated in Hayat-1 well to determine the lithology of rocks and possibility of hydrocarbon accumulation. The volume of shale percentage along the well ranges from 10 to 40%. Meanwhile the depth ranging from 2020 to 2039 m are occupied by clay deposits, in which the values reach more than 75%. Different new applications using spectral gamma-ray logs, as thorium normalization and radiogenic heat production were applied to determine hydrocarbon accumulation zones and differentiate between source and reservoir rocks. The results of radioactive techniques agree well with the results of reservoir parameters, which were calculated from conventional logs, by a percentage ratio that reach more than 80%.

Estimation and mapping of Arias intensity in Nepal: Insights from seismic analysis in the Kathmandu Valley

2025-03-29T13:48:59+00:00

Kathmandu Valley, the capital of Nepal, is located in the seismically active Himalayan belt and has a history of devastating earthquakes causing substantial loss of life and property damage. This study employs Probabilistic Seismic Hazard Analysis (PSHA) using the Foulser-Piggott Attenuation (FPA) model and Travasarou et al. (2003) with R-CRISIS software to calculate Arias intensity in Kathmandu Valley. Historical and recent seismic data within a 500-km radius were analysed, and the earthquake catalogue was declustered and standardized using ZMAP software, a tool developed for the statistical analysis and visualization of earthquake catalogues. Additionally, a Digital Elevation Model (DEM) based topographic analysis was conducted to assess the impact of local topography on seismic site response providing insights into, slope, soil amplification factors, and shear wave velocity across the region. The results reveal Arias intensity values ranging from 0.225 to 0.241 m/s at 2% and 10% probability of exceedance corresponding to 475 and 2475 years, mapped using ArcGIS. The analysis revealed that southwestern Kathmandu and Lalitpur exhibit higher Arias intensity values, while intensity decreases gradually from southwest to northeast. The DEM analysis further revealed that areas with low slopes, particularly in central Kathmandu, have higher soil amplification factors, potentially amplifying seismic waves. The shear wave velocity distribution highlights lower values in sedimentary deposits, indicating increased seismic vulnerability. These findings emphasize the need for effective urban planning and disaster preparedness strategies to mitigate earthquake impacts in Kathmandu Valley.

Principles of imaging subsurface magnetic susceptibility with application to synthetic and field examples

2025-03-29T13:49:01+00:00

In this study, a simple new methodology for imaging subsurface magnetic susceptibility from three-dimensional (3-D) correlation tomography of magnetic data is presented. This methodology can be used to rapidly evaluate the equivalent subsurface magnetic susceptibility distribution, especially when powerful commercial programs are unavailable. In correlation tomography, the region of interest is divided into a regular 3-D grid, and the correlation is then calculated between the measured magnetic field data and the computed magnetic field data resulting from a magnetic point dipole. A probabilistic estimate of the distribution of the equivalent magnetic dipoles can be achieved using the correlation coefficient technique. The coefficient values range between −1 and +1 and are equivalent physical parameters. The cross-correlation values obtained at different depth intervals are plotted to show that the higher the correlation coefficient, the greater the equivalent magnetic dipole distribution and vice versa. The computer program was tested on both synthetic magnetic data and on real field data acquired over the west Garida and Hamama deposits in Egypt's Eastern Desert. Overall, the cross-correlation tomography approach yields quick, efficient results that can be used as a basis for subsequent in-depth modelling.

Correlation of time-different ground radiometry datasets on an example of fault survey (Hradište border fault, Turiec Basin, Western Carpathians, Slovakia)

2025-03-29T13:49:02+00:00

Complex geophysical survey (seismic tomography, electrical resistivity tomography and electromagnetic interference measurement, spontaneous potential, ground penetration radar, gravimetry, magnetometry and radiometry) was carried out along 450 m-long profile crossing the assumed map track line of the Hradište border fault to specify its position and some of its features. As a result, a 115 m-wide fault zone was identified, vertically or steeply dipped to the south-east and east. Because of incompatibilities between the results of deep-range geophysical methods (seismics, geo-electrics, gravimetry and magnetometry) and the results of shallow-range radiometric methods (ground gamma-ray spectrometry and soil radon emanometry), the latter were measured twice, in 2012 and 2016 years. The comparison of results of both radiometric measurements shows an acceptable level of linear correlation mainly for thorium concentration (R = 0.87), gamma dose rate (R = 0.84), radon activity concentration (R = 0.69) and potassium concentration (R = 0.66), but very low one for uranium concentration (R = 0.12). Alongside, no correlation between soil uranium concentration and activity concentration of radon in soil air was determined. These results confirm the behaviour of measured radiometric quantities in soils and weathered rock covers, and strong influenceability mainly of uranium and radon presence in shallow subsurface horizon by changing meteorological conditions.

The use of space geophysics data to establish a subsurface structural frameworks map on East Uweinat ring complexes province, Southwestern Desert, Egypt

2025-03-29T13:49:04+00:00

The study focuses on the east Uweinat area in the eastern sector of the Saharan continental crust and extends to the Arabian-Nubian basement rocks in the east. This area extends beyond the Egyptian territories, including the northern part of Sudan and the eastern part of Libya. The Saharan continental crust represents a challenge due to its classification as an arid to hyper arid environment and the difficulty of accessing it. The study aims to construct the regional structural framework of the basement complex that has its influence on the overlying sedimentary section, specifically in the part that belongs to the Saharan continental crust of Egypt. Space geophysical data was used, including GRACE, magnetic, SRTM Gravity Recovery and Climate Experiment, Earth Magnetic Anomaly Grid, Shuttle Radar Topographic Mission and geoid data. A qualitative and quantitative interpretation is used to highlight the subsurface geological picture and structure framework. The integration of these data helps to understand the subsurface structural framework and provide insights into the geological evolution of the region. The constructed structural framework map shows the presence of a large basin east of the Uweinat area, mainly sourced from the Nile River and a small amount of rainfall, with geological obstacles preventing water leakage out. The occurrence of the East Uweinat ring complexes and volcanism have both positive and negative impacts and must be taken into account in any systematic natural resources exploration strategy.