Acta Geodaetica et Geophysica最新文献

With the rapid growth of the construction industry, precise and efficient monitoring of building deformation has become a crucial factor in ensuring their secure construction and stable operation. The frequent occurrence of occlusion and diffraction errors in satellite signals caused by high-rise buildings has emerged as a primary challenge that constrains the accuracy of positioning in deformation monitoring by BeiDou Navigation Satellite (BDS). To solve the problems, this study proposes an elevation mask angle modeling method of satellite signal occlusion based on azimuth rounding and applies it to real-time BDS building deformation monitoring and positioning algorithm. The proposed approach involves defining a particular subset of integer azimuth and elevation angles, followed by utilizing the minimum elevation angle from this subset to develop a model for the azimuth-dependent elevation mask angle. We aimed to develop an elevation angle mask model using a conventional approach, and the model can be utilized to focus on non-line-of-sight (NLOS) and multipath signals and attenuate their impact on positioning accuracy by reducing their weight. The experimental results show that the elevation angle mask model can be easily completed by using the observation data of BDS satellites in a single day, and its use can make the number of effective satellites involved in the calculation of real-time deformation monitoring of BDS more accurate and reliable. The root mean square (RMS) of positioning results including float solutions was increased respectively by 91.1%, 93.3%, and 72.7% in the direction of East-North-Up (ENU), and the RMS of results with fixed ambiguity was increased by 6.9%, 10.0%, and 29.5%, respectively. Therefore, it can be concluded that the elevation mask angle modeling algorithm is convenient to realize and can significantly improve the performance of deformation monitoring results by BDS.

The aim of this work is to investigate whether retrieving the model parameters of self-potential (SP) anomalies using a combination of differential evolution (DE) and particle swarm optimization (PSO) is possible. This approach hybridizes DE and PSO in a parallel way. Each algorithm is self-contained and obtains a [premature] solution after a user-defined generation number. This hybrid algorithm (DE/PSO) selects the best individual in DE and PSO populations and carries it to the next iteration. Cooperation of DE and PSO can significantly improve the results. Simulations through noise-free synthetic anomalies show that the DE/PSO hybrid algorithm is successful in providing more accurate solutions than those obtained using each single metaheuristic. The algorithm also speeds up the rate of convergence to get the optimum solution. We implemented the algorithm in R programming environment using available metaheuristics packages. Then, the reliability of the code was investigated using some mathematical test functions having two and higher dimensions (unknowns). The performance of the hybrid to invert SP anomalies was tested by synthetic and field data sets. The true model parameters were well-recovered from synthetic data sets including noise-free and noisy data. In the tests with field data, SP anomalies over a shallow ore deposit in Süleymanköy (Türkiye), a deep ore deposit in Arizona (USA), and multiple sources of graphite deposits in KTB borehole site (Germany) were inverted. Low misfit values between the observed and calculated SP anomalies were obtained during the test studies.

Especially after the March 4, 1977 disastrous Vrancea earthquake (Mw 7.4), the necessity for a detailed local seismic hazard map for Bucharest, the capital city of Romania, was recognized. The distribution of earthquake effects as well as subsequent earthquake recordings throughout the city revealed a high variability of seismic ground motion, not only due to source effects but also due to local site effects. The geophysical methods employed in recent years allowed only limited results, so that there are no general geological models of the city applicable to a city-wide analysis. By using a recently compiled geological database, which relies mostly on several hundreds of borehole measurements performed for the subway in Bucharest and a recent DEM for the area, this study establishes the positions of the main seven Quaternary layers beneath the city. A 3D geological model is obtained by interpolation using the GIS kriging method. The 3D geologic model covers most of the city area, reflecting the confidence boundaries. This study also discusses geotechnical data availability and the influence of hydrogeology on the analysis of microzonation of the Bucharest city area.

The seismic response obtained at the ground level can be quite different in terms of load characteristics compared with incident wave applied to the bedrock. These changes may be due to soil conditions and topography of the area. In this study, a practical approach is proposed in the frequency-domain to evaluate two-dimensional seismic ground response using transfer functions. To use the formulation of the proposed approach, a program was written called “2DTF”. The linear 2DTF software is promoted to equivalent linear program, and then two real cases of the Adames region during September 7th, 1999 earthquake are adopted for further study. These case studies have different characteristics, including free fields and areas where topography has a direct effect of changing the nature of the incident seismic waves. The superiority of the proposed two-dimensional over the conventional one-dimensional methods (despite its simplicity and practicality) is its capability to simulate different soil layering conditions and surface irregularity with high speed and accuracy. Numerical case studies show that using the 2DTF program provides reasonable and consistent results with local observations as well as verified research.

The Pannonian basin is an extensional back-arc basin that has undergone neotectonic inversion and is currently shortening. The understanding and quantification of present-day deformation processes during this inversion are still incomplete. To this end, we investigate the active deformation of the Circum-Pannonian region via the interpolation of GNSS-derived velocity field and the derivation of the strain rate fields. For the interpolation of the velocity field, we use ordinary kriging, a strochastic interpolation method. Our results show that estimating a strain rate field that is virtually free of short-wavelength noise requires the scaling of the velocity uncertainties, i.e. assuming a minimum standard deviation of 1 mm/yr in our case. The deformation of the Circum-Pannonian region is defined by the 2–3 mm/yr, NNE-directed motion of the Dinarides, and by the 0.5–1.5 mm/yr, WSW to SSW directed motion of the eastern areas (European foreland, East Carpathians, South Carpathians, Transylvanian basin). These opposite-sense motions define a large-scale, on average NE-SW shortening and transpression-type deformation in the Dinarides as well as in the Pannonian basin, while the East and South Carpathians undergo regional N–S extension. Neotectonic structures generally show good agreement with the strain rate field, for example in the Dinarides, Eastern Alps, or in the western Pannonian basin. However, the presence of fault-parallel shortening or biaxial shortening along sinistral neotectonic structures in the central and eastern Pannonian basin show some discrepancy between current geodetic and observed neotectonic deformation. The vertical velocity field shows dominantly 100 and 1000 km wavelength signals, the former is probably related to the response of the Pannonian lithosphere-asthenosphere system to neotectonic basin inversion, while latter can possibly be explained by far-field subsidence patterns induced by the mantle response to melting of the Fennoscandian ice sheet during the current interglacial period.

Natural stones are exposed to sudden and slow-developing thermal cycles, affecting their physico-mechanical and surface properties. In this study, changes in the physico-mechanical properties of natural stones in response to sudden (thermal shock) and slow-developing (thermal aging) thermal cycles were investigated on natural stone samples with various compositions (magmatic, sedimentary, metamorphic). Both the thermal shock and thermal aging cycles were simulated by first heating the specimens to 105 °C for 18 h. In case of the thermal shock cycles, the heating phase was followed by placing the samples in purred water for 6 h. To simulate the thermal aging cycles, specimens were allowed to cool at room temperature (23 °C) for 6 h. At the end of the cycles, a selection of physico-mechanical properties was evaluated and compared with the initial values. Results indicate that thermal treatments have a significant negative effect on the strength of the natural stone samples. Regression models were developed to estimate uniaxial compressive strength, point load strength, Brazilian tensile strength from non-destructive test parameters (Schmidt hardness, P wave velocity, porosity) of natural and treated samples. Results show that there are strong correlations between mechanical properties and non-destructive test parameters (R² > 0.96, MAPE values between 2 and 5%).

The present study carries out subsurface exploration of Jamshedpur region using Active Multichannel Analysis of Surface Waves techniques that provide information on the different lithological characteristics. Four different sites (MASW-1 to MASW-4) were chosen in proximity to river basin to obtain a probable shear wave velocity profile. To record the raw wave field traces produced by a 10 kg sledgehammer, a linear array of 24 numbers of 4.5 Hz geophones was employed. The effects of data acquisition parameters, like sampling frequency (500 Hz, 1000 Hz, and 2000 Hz) and offset distance (1 m, 6 m, 8 m, and 20 m), were used to obtain a high-resolution dispersion image. Due to the variables selected as data acquisition parameters, the optimal set of data parameters was found, providing the best resolution of dispersion images for all the selected sites. The results indicate that the best resolution of the dispersion image was produced at an offset distance range of 6–8 m at sampling frequencies range of 500–1000 Hz at 1 m geophone spacing with five stacking, indicating a strong signal to noise ratio in a range of 80–90%. Up to a depth of ~ 3 m, stiff silty clay soil was discovered, and at depths of 30 m or more, medium- to very-dense weathered mica schist was discovered. At sites MASW-1 and MASW-3, respectively, slag fillings were found in the top layer at depths of 1.2 and 2.3 m. Greater depths of hard rock layers have also been found at site MASW-3. Locations along the river generally fall into National Earthquake Hazards Reduction Program (NEHRP) categories C or D.

Previously drilled boreholes of a host rock for a potential nuclear waste repository in Hungary revealed a highly fractured claystone rock body. A crucial step for characterizing the hydrodynamic behavior of such a fractured reservoir is fracture identification and accurate calculation of the fracture density. Although acoustic borehole televiewers provide a reliable base for determining the fracture density, older boreholes usually lack such data. However, conventional borehole geophysical measurements are often accessible in such cases. The aim of this study was to identify any correlations between well log data and fracture density. Multiple linear regression analysis was performed on data from two boreholes penetrating the Boda Claystone Formation in southwest Hungary. The upper section of the BAF-4 borehole was used for training, where the fracture density was estimated with a fit of R² = 0.767. The computed regression function predicted the fracture density with high accuracy in both boreholes for all intervals with typical lithological features. However, in some sections where anomalous well log data indicated changes in the lithology, the prediction accuracy decreased. For example, the function underestimated the fracture density in sandy intervals.

El-Bakriya area is situated in the Central Eastern Desert of Egypt. It includes several mineral occurrences and/or deposits. Data from remote sensing and airborne geophysics (gamma-ray and magnetic) were combined to identify the hydrothermal alteration zones and structures related to these occurrences. Various processing of ASTER satellite images revealed fifteen zones of high probability for metallic mineralizations. Airborne gamma-ray spectrometric data clarify K-enrichment zones, which are correlated geologically with the distribution of calc-alkaline, alkali feldspar granites (Younger granites), and calc-alkaline quartzdiorites to granodiorites (Older granites), as well as basement metavolcanics and metasediments. An integrated hydrothermal alteration map was constructed, based on both ASTER remote sensing and airborne gamma-ray spectrometric data. This map delineates some metallic mineral occurrences and/or deposits, which are located in the detected hydrothermal alteration zones. Besides, it displays new potential zones for mineralization, such as: Gabal (G.) El-Shalul, G. El-Bakriya, G. Siwat El-Arsha and G. Umm Bisilla. The geologic and airborne magnetic maps demonstrate five structural lineament trends of E–W, ENE–WSW, NE–SW, NW–SE, and NNW–SSE directions, which might act as pathways to transport the hydrothermal solutions in the study area.

This work presents a technique to transform a global spherical to an adjusted local rectangular harmonic model. First, the mathematical form of a global spherical harmonic model is presented. Second, the necessary conversion from global (geocentric) into local rectangular coordinates is given. Third, Laplace’s equation is solved by the method of separation of variables in local rectangular coordinates and its solutions in different functional forms are presented. Then, the estimation of the coefficients of these mathematical models by a least squares’ adjustment process is described, using as data the values of the disturbing potential of the Earth’s gravity field. The strategy for the selection of the best mathematical model for a successful transformation is described and validated in different case studies. These refer to areas in Greece, China and Germany and include comparisons with other models or methods. The results show the applicability of the presented transformation and confirm its advantages.