Acta Geodaetica et Geophysica最新文献

Adding local, precise geodetic datasets is necessary to improve the accuracy and performance of Global Geopotential Models (GGMs). Consequently, GGMs could be utilized in geosciences, geodetic, and geomatics applications, particularly in developing countries where no accurate geoid model is affordable. Typically, the discrepancies of geoid undulations at Global Navigation Satellite Systems (GNSS)/Levelling stations are utilized to establish a correction surface within a Geographic Information Systems (GIS) environment. The current research proposes a new approach that depends on taking into account both GGM errors in geoidal undulations and free-air gravity anomalies over a particular local region. This method has been carried out in the Nile Delta region, north of Egypt, utilizing 160 GNSS/Levelling stations and 20 terrestrial gravity points. Two GGM models have been investigated as candidates for high-resolution global models, namely the EGM 2008 and the SGG-UGM-2 models. The accomplished results showed that the traditional approach enhances the EGM2008 by 21% while the proposed weighted approach yields 45% improvements. Less enhancement has been reported for the SGG-UGM-2 model. The proposed approach does not require more local datasets and consequently no more economic costs are needed. Moreover, the processing methodology of that approach is quite straightforward, which means that it could be performed in other developing countries to enhance the performance of GGMs.

In this paper, we propose and apply a novel numerical approach for modeling the gravitational field by solving the coupled interior-exterior boundary value problem (BVP) using the finite element method (FEM). To this end, we construct a finite computational domain encompassing the selected celestial object and a bounded portion of its exterior, within which the BVP is formulated. This problem consists of the Poisson equation for the gravitational potential, along with a Dirichlet boundary condition (BC) prescribed on the boundary. In this case, since the boundary is placed far from the object so that the Dirichlet BC is nearly zero, the only key input for the computation is the 3D model of the celestial body and its density. The solution is derived using the FEM, which is particularly effective for handling highly irregular or complex surface geometries. The numerical experiments include a test case involving a homogeneous sphere to demonstrate the second-order accuracy of the proposed approach as well as simulations of the gravitational fields of two selected asteroids, namely 25143 Itokawa and 433 Eros, and the comet 67P/Churyumov-Gerasimenko. These simulations yield detailed three-dimensional distributions of both gravitational potential and gravitational acceleration within the entire computational domain.

Water inrush is the second greatest threat among the most frequent accidents associated with mine production. To address the changes in permeability and stability in the burnt area of the Shennan mining area, in this study, triaxial compressive and permeability tests were conducted on burnt rocks with whose acoustic emission (AE) characteristics were collected. Further analysis was conducted on the correlation among the strength properties, permeability evolution and AE characteristics of the burnt rocks under fluid–solid coupling conditions to reveal the permeability evolution of the burnt rocks. The testing results indicate that the four stages of permeability changes are related to different regions of the stress-strain curves. The AE damage variable begins to increase, and the effects of cracks on permeability, stress-strain curves, and AE ringing counts gradually increase with the development of cracks. The permeability increases rapidly in near the initiation stress (σ_ci), revealing that crack initiation and growth induce an increase in the permeability of the burnt rock. Specifically, the permeabilities of the burnt rock at yield stress (σ_cd) are 3.24, 3.21 and 3.04 larger than these at initiation stress (σ_ci) with the confining stresses of 2, 5 and 8 MPa. Consequently, monitoring the stress and AE signals of burnt rock masses with mining stress disturbances and preventing and controlling water inrush risk in the hidden burnt rock area in the Ningtiaota coal mine of the Shennan mining area are important.

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Geo-electrical methods, including electrical resistivity and induced polarization, are key tools for the identification and assessment of mineral deposits, particularly gold. In this study, nine electrical profiles were surveyed in a region characterized by volcano-sedimentary outcrops and silicic dikes in northeastern Azerbaijan. The data underwent inversion modeling using two meshing approaches: structured (quadrilateral) and unstructured (triangular), allowing for an evaluation of their effects on the interpretation of subsurface electrical characteristics. The results indicated that unstructured modeling provided superior resolution and lower error compared to structured modeling in areas of rugged topography, yielding a more accurate depiction of gold-related sources. The analysis revealed a strong correlation between resistivity and induced polarization data with the presence of gold in vein-hosted mineralization and hornfels units. Furthermore, two distinct mineralization trends were identified: a shallow trend associated with sulfides in hornfels and a deeper trend linked to silicic veins, both closely aligned with gold grades and modeling patterns. In addition, the alignment of anomalies with regional fault structures and mineralizing fluid pathways confirms the area’s substantial potential for gold mineralization within low-sulfidation epithermal systems. Ultimately, the findings suggest that the combination of unstructured meshing and inversion modeling can serve as an effective tool for high-precision mineral exploration in geologically complex regions.

A bivariate polynomial is an important type of explicit function that can approximate a physical quantity that varies continuously and smoothly over a surface. Such functions can be derived by successive least-squares optimisations which determine which terms are statistically significant, the results being designated as multiple regression equations (MREs). One application is coordinate shifts from one geodetic positioning system (datum) to another. Recent research has found accuracy benefits from partitioned MREs in which two polynomials are joined together smoothly, reducing the need for high-power terms. Case studies from that research suggested that partitioning should be across whichever of the north–south and east–west extents was the greater. The paper investigates whether diagonal partitioning is best for data in oblique territories (where the line of greatest extent is diagonal). The case study selected was coordinate transformations in Slovenia which is relatively oblique. Oblique partitioning was not in itself an improvement on east–west partitioning but became so when contributing to two hybrid models. More research is needed but results so far suggest that the best course is to test all partitioning options and apply the one that gives the closest fit to the particular data.

Based on earthquake data from the Shandong Seismic Network from August 6, 2023, to September 14, 2023, the source physical parameters of nine M_L ≥ 2.5 earthquakes in the Pingyuan seismic sequence are initially calculated based on the Brune model. Then, the earthquakes in the Pingyuan seismic sequence are located using the double-difference earthquake location algorithm (DDELA), and the focal mechanism of the mainshock is inverted via the cut-and-paste method. Finally, the source parameters of the Pingyuan earthquake and the rupture process are analyzed. The results show that the M_S 5.5 Pingyuan mainshock exhibited a substantial stress drop, which was notably higher than the typical global average of 4 Mpa. This was accompanied by a large source rupture radius and a significant release of energy, indicating that this seismic event occurred under high-stress environment. This may explain the great damage observed near the epicenter and the intense surface shaking. According to the DDELA results, the focal depth of the mainshock was approximately 19.9 km, and the focal depths of the aftershocks were mainly distributed in the range of 18–24 km; the focal depths were distributed in a nearly vertical banded zone, indicating a steeply dipping fault plane. The large focal depths were attributed to the thick loess cover in the Pingyuan area, which is part of the sedimentary plain of the Yellow River. Based on a comprehensive analysis of the focal mechanism solution of the M_S 5.5 Pingyuan earthquake and the spatial distribution of the precisely relocated hypocenters of the aftershocks, the M_S 5.5 Pingyuan earthquake was generated by a right-lateral strike-slip fault striking NE–SW under principal compressive stress oriented in the ENE direction. The main seismogenic structure of this earthquake was the NE-trending Lingxian–Guanxian fault, which is a right-lateral strike-slip fault with a high dip angle. Moreover, the temporal variation in the stress drop in the aftershock sequence reflects the adjustment process of the stress environment in the source area. In the early stage after the M_S 5.5 earthquake, due to the large release of stress by the M_S 5.5 mainshock, the source area overall experienced low-stress conditions for a short period, and many aftershocks occurred in this low-stress environment. Two days after the earthquake, as the stress environment in the source area gradually adjusted, the regional stress level returned to near the normal value; that is, the various blocks in the source area reached relative equilibrium. Therefore, no subsequent major seismic event occurred.

We study the variation of zenith total delay (ZTD) and precipitable water vapour (PWV) using global positioning system (GPS) data and observed meteorological information over three different topographical zones of Nepal: Terai, Hilly and Himalayan region. Eight GPS stations scattered across these regions were utilized for data collection. Two alternate years, 2015 and 2017 were taken as the study period and the data obtained were analysed to compare trends. Findings indicate that the average PWV levels are higher in the Terai region in comparison to the Hilly and Himalayan region, explaining the precipitation patterns over Nepal. Additionally, the daily PWV patterns show peak levels during mid-day and a decline during the night. The findings highlight the significant variability of PWV across different regions of Nepal and its implications for evaluating PWV variability across regions.

This paper introduces a technique for modeling the gravity potential using a low-degree Taylor series expansion, specifically of three or four degrees and demonstrates its practical application. The coefficients for this gravity model are the derivatives of the gravity potential at a specified point. The coefficients are determined through Von Eötvös’ torsion balance measurements conducted on the ice sheet of Lake Balaton in Hungary, by minimizing the squares of the difference between the nearby measured (by torsion balance) and calculated second derivatives of gravity potential. The model is applicable over an area spanning several kilometers, encompassing multiple torsion balance measurements, and thus provides broader coverage compared to a strictly local model, thereby justifying its classification as a sub-regional model. The resulting gravity potential field is presented on two types of map, similarly to Eötvös’ work. The derived model characterizes the gravitational potential for the region where measurements were taken, yet it behaves unexpectedly and generates artifacts beyond this measurement area. Earlier geoid models for this region included torsion balance data; in contrast, our results provide a more detailed gravity potential model over a more confined area.

In this study, a widely used moment tensor decomposition scheme and source-type plot diagrams are applied to determine the source type and mechanism of recent earthquakes in northwestern and southern Egypt. First, the full-waveform moment tensor inversion is conducted to determine the optimal faulting mechanism using an appropriate 1-D structural velocity model. Second, the complete moment tensors are decomposed into deviatoric (DEV) and isotropic (ISO) components. The earthquakes in the northwestern Dahshour region exhibit ISO components ranging from 9.2 to 38.7%, while those in the Aswan region have ISO components ranging from 2.6 to 56.4%, indicating tensile/compressive nature of fracturing. This suggests that in the Dahshour region, cracks may open or close at the source due to fluid extraction and/or injection. Similarly, earthquakes in the Aswan region are likely influenced by the charge/discharge circulation of the High Dam reservoir. Our findings suggest that in addition to natural dynamic and tectonic factors, secondary anthropogenic influences play a role in controlling seismic activity in the investigated regions. Identifying the source type and mechanism of non-double-couple earthquakes is crucial for time-dependent seismic hazard assessment, particularly in areas where large-scale fluid operations are ongoing.

The paper aims to investigate the geological structure of the Gulf of Saros and Gelibolu peninsula by using airborne magnetic data. To this end, derivative methods such as the second vertical derivative and tilt method have been applied to these data and created the anomaly maps. By a closer look at these maps, it is observed that there is an intense linear magnetic anomaly parallel to the shoreline of the Çanakkale Strait. This intense anomaly can be correlated with the Ganos Strike-slip Fault observed in the north-western part of the active tectonic map of Türkiye. In addition, the depth estimations utilizing the half-width method for simple geometric bodies suggest a deep source in the southwestern profile and a shallow source in the northeastern profile. As a result, it can be deduced that the magmatic material arising from the magma fills inside the strike-slip fault causing this magnetic anomaly. Such sources with deep roots could be prospective for geothermal energy as well as hydrocarbon maturation.