查看更多>>摘要：A major challenge in geosciences is the acquisition of high-resolution geophysical data that could help to better understand the Earth's interior and processes. In this study, we develop a Tailored Gravity Model (TGM) to fit local terrestrial gravity data collected throughout the Southern Benue Trough (situated in southeast Nigeria) by using Global Gravitational Models (GGMs), terrestrial gravity data, and Digital Elevation Models (DEMs). Specifically, we develop the TGM by computing gravity values from the XGM2019e_2159 global gravitational model on the topographic surface generated by using the Multi-Error-Removed Improved-Terrain (MERIT) DEM topographic heights, and algebraically adding the residual gravity effects obtained from the SRTM2gravity global model of spherical gravimetric terrain correction, while removing a detected systematic bias. An independent statistical evaluation of the terrestrial and tailored gravity data shows that most of the differences between these two datasets are within & PLUSMN;10 mGal, while the RMS of differences improved from 16.7 to 6.4 mGal and a systematic bias was removed. We used the tailored gravity data to compile the Bouguer gravity map. The gravity map produced from a high-resolution absolute gravity data reveals the spatial gravity pattern that is likely associated with aquifers and magmatic structures within the Southern Benue Trough. In agreement with published studies, the Bouguer gravity map demonstrates the folding, faulting, and upwelling or uplifting of the crust. Our gravimetric interpretation suggests that the elongated gravity high along the flexurally inverted and circular Abakaliki Anticlinorium in the Bouguer gravity map could indicate a possible existence of a reservoir of mineral ore bodies or mineral-bearing rocks.
Vieira, Andre LuizBraga, Marco Antonio da SilvaBarbosa, Marcelo RobertoKoppe, Jair Carlos...
8页
查看更多>>摘要：Carajas mineral province, Para State, Brazil, is one of the world's largest producers of iron ore. The study area is located inside this province at the S11D Mine in its southern portion. The iron ore is composed by banded iron formations (BIFs), consisting basically of hematite and jaspilite bodies. The weathering processes promoted formation of blocks of jaspilite immersed in friable hematite. The current methodology applied in the production benches, using just drillhole investigations, is limited to detect boulders of compact rock, that depending on their sizes, can compromise the Truckless System operation making it costly and unproductive. Electrical and electromagnetic dataset were able to differentiate these two types of materials, one, more conductive (<8000 Omega-m), with attenuated signal in the GPR section associated with jaspilites and another, most resistive (> 8000 Omega-m) with the coinciding contrasted signal from GPR sections associated with the friable hematite. The near surface geophysical dataset interpretation constrained by a detailed bench geological mapping, was capable to solve the referred problem by indicating the location of the compact bodies through the interpretation of the 3D resistive / reflective models, enhancing geological model and rescaling blast design. The final Geophysical model guided the optimization of the blasting design with geometric and energetic improvements.
查看更多>>摘要：The Huangling Anticline, which formed during the Jinning movement, is the structural core of the Yangtze River Three Gorges area. In this study, we investigated the geological structure of the Huangling Anticline through correlation analysis among magnetic, Bouguer gravity, and crustal susceptibility anomalies of the Three Gorges and adjacent areas. Aeromagnetic anomalies, which were processed by reducing to the pole, reveal four main aeromagnetic anomaly regions. Three-dimensional (3D) magnetic susceptibility constrained inversion was used to obtain the susceptibility distribution from 0 to 30 km depth. We focused on the spatial distribution of four major rock masses: Sandouping, Huanglingmiao, Dalaoling, and Xiaofeng. The low susceptibility of the Huanglingmiao rock mass is tentatively explained by the combined effect of weathering and stripping of the upper body and a tectonic ductile shear zone at the bottom.
查看更多>>摘要：ABSTR A C T Edge detection methods based on derivatives of potential fields have been commonly utilizing to interpret the potential field data. Although these techniques are very useful tools for determining subsurface lineaments, they have some limitations such as sensitivity to noise, thick or diffuse detected boundaries and blurred edges. In this study, the Kuwahara filter, an edge enhancement operator which has smoothing, edge preserving and edge sharpening effects, is proposed to enhance the boundaries in the potential field data without above-mentioned limitations. Three synthetic model applications are made to demonstrate the mentioned advantages of the Kuwahara filter. The effect of the window size on the filter response has been studied and demonstrated in detail. After that, the total horizontal derivative, analytic signal and vertical gradient of the Kuwahara filter responses of the noisy synthetic gravity dataset have been calculated and compared with those calculated from the original data. In addition, it has been shown that the results can be further improved by applying the Gaussian smoothing to the Kuwahara filter responses. Finally, the Bouguer gravity dataset compiled from Konya-Beys,ehir region in Turkey have been utilized to show the performance of the Kuwahara filter on real data. Both synthetic and real data applications have shown that more clearly edges and detailed results can be obtained from the datasets filtered by using the Kuwahara and Gaussian filters.
查看更多>>摘要：In order to effectively suppress large-scale strong interference and retain the useful low-frequency information of the measured magnetotelluric (MT) data, a new method of MT signal-noise separation based on sparsity adaptive stage-wise orthogonal matching pursuit (SAStOMP) is proposed. To demonstrate this technique, pulse atoms, cosine atoms and other atoms were used to build an over-complete dictionary, and fuzzy entropy was applied to control the sparsity of improved stage-wise orthogonal matching pursuit (IStOMP) algorithm, thereby realizing adaptive sparse representation. Then, we utilized SAStOMP to suppress strong electromagnetic interference and reconstruct useful MT signals. The technique was validated through simulated typical strong interference and measured MT data in ore district. The findings have proved that the proposed method can effectively eliminate large-scale strong interference and retain low-frequency useful signals in comparison with conventional methods such as remote reference (RR), orthogonal matching pursuit (OMP), and stage-wise orthogonal matching pursuit (StOMP). The obtained apparent resistivity-phase curve is smoother and more consistent, and the reflected underground electrical structure is more realistic and reliable.
查看更多>>摘要：Reverse time migration (RTM) is the important intermediate step for focusing the radar diffracted energy of the targets in ground penetrating radar imaging. The conventional RTM algorithm demands a large number of iterative trial experiments and depends on the experts' decision on the estimation of the velocity or relative permittivity of the subsurface medium. Meanwhile, the RTM profile is vulnerable to artifacts, which are composed of noise interference, multiple interferences, arc-shaped clutter, and crosstalk, so it is difficult to inspect visually. Therefore, we propose a RTM method based on accurate velocity estimation and total variation (TV) de-noising to improve the accuracy of the RTM imaging. Firstly, the appropriate migration velocity is obtained automatically by autofocusing metrics to reduce the number of visual inspection times and corrections in the migration processing. Secondly, the TV de-noising strategy based on split Bregman iterative is applied to the RTM profile with the cross-correlation imaging condition, so that the edge of the target can be obvious and the position can be accurate. Then, we apply the proposed method to the simulation data of the pipeline model and the tunnel lining model. All results show that the selected three different autofocusing metrics have unimodality and unbiasedness, which can focus on a single relative permittivity to obtain appropriate migration velocity. Furthermore, the TV de-noising strategy successfully eliminates artifacts, reconstructs contours, enhances the edge sharpness, and improves the quality and accuracy of the radar profile. Finally, we take the field data of the LiuYang River tunnel to verify the applicability of our method, we choose 2-30 as a wider range of relative permittivity based on prior information. Considering the different lateral velocity of the field data, we adopt lateral segmentation processing to improve the quality of the GPR profile. The tests of simulation data and the field data indicate that the proposed method can provide a scientific and effective way for accurate interpretation of GPR data.
Deshmukh, V.Kumar, P. V. VijayaRao, P. B. V. SubbaKumar, Amit...
11页
查看更多>>摘要：Thermal springs of Aravali, Tural and Rajawadi are located in the Deccan volcanic province (DVP) in the western part of Maharashtra, India and are covered by Deccan basalts. These springs run parallel to the Western Ghats and geochemical studies denote that these hot water springs are of meteoritic origin that emerge from basement rock.To understand the geoelectric structure and possible source zone of hot water springs, a 26-station audiomagnetotelluric (AMT) survey was carried out along E -W profiles across Aravali, Tural and Rajawadi geothermal springs with a station spacing of about 1-1.5 km. A 2D inversion was carried out jointly for transverse electric (TE) and transverse magnetic (TM) data after the distortion and decomposition analysis.These geothermal zones appear as high conductive zones at shallow depth and are associated with fault/ fracture zones within the sedimentary basin. The basement depth increases from 1 km to 2.5 km moving from Aravali to Rajawadi geothermal zones. Volcanic plugs at a shallow depth beneath Tural and Rajawadi thermal springs act as a source rock for heat. Thus, hot water temperatures are higher for these two thermal springs relative to Aravali thermal spring, which is devoid of magma intrusion and related to circulation of meteoric water over basement.
查看更多>>摘要：Multi-component high resolution seismic reflection data were acquired at the Uppsala University field test site in Marsta, Sweden, in March 2019 with the aim of obtaining an improved understanding of the subsurface structure in the area. An advantage of the site is that a number of boreholes have been drilled there for both hydro geological and geophysical purposes, allowing surface geophysics to be compared with downhole information. The presence of a low velocity layer above the water table generates significant processing challenges due to trapped waves. A further complication with the data is that the upper part of this layer was frozen at the time of the survey, resulting in the sediments just below the surface having a significantly higher velocity than those below. By analyzing and processing both the vertical and radial component data it was possible to build a velocity model that is consistent with the observed data. A strong PS converted reflection allows the bedrock to be imaged on the radial component stacks to much higher resolution than on the vertical component stacks. Both common conversion point binning and pre-stack depth migration were used to process the radial component data. We confirmed that our processing strategy was effective by generating synthetic data that were processed in a similar manner as the real data. The PS images indicate a step in the bedrock of about 2 m, with depth to it increasing from about 15 m to 17 m close to one of the boreholes. This step is not observed on the PP stacks, due to their lower resolution.
查看更多>>摘要：When the traditional sea surface towed multi-channel seismic technology is applied to the deep-water stratum exploration, the Fresnel radius of the target stratum is large due to the large-depth water bodies, greatly reducing the horizontal resolution. Hence, it is difficult to achieve high-resolution exploration with the traditional technology and cannot meet the requirements for high-precision exploration and orebody description of such deep water seabed resources as natural gas hydrate (NGH). The near-seabed deep-towed seismic exploration technology was proposed to solve this problem. This paper introduces a set of high-resolution deep-towed seismic system being developed in China, Kuiyang ST2000. The remarkable difference between the equipment and foreign counterpart is that this equipment uses a deep-towed sparker instead of a resonator source. We systematically describes the system composition of the deep-towed system, and primarily discusses the technical design of the deep-towed sparker which can still have relatively large stratum penetration depth in deep-water and high-static-pressure environment. In addition, we also introduces the unique continuous acquisition technology possessed by the system. At present, the experiment of 2000 m deep-water depth has been carried out for this system, and the experimental and related data processing results show that this equipment has had fundamental functions. Several deep-water experiments will be carried out in the next step.
查看更多>>摘要：The use of unsupervised machine learning methods such as K-means, Hierarchical Agglomerative Clustering, and Self-organizing maps is constantly increasing in seismic interpretation. Regarding unsupervised methods, the Kmeans technique is one of the simplest ways to cluster seismic facies, although it presents neither a structure between the generated labels nor a measure of similarity when considering their order. To solve this drawback, we propose two automated label organization techniques that use principal component analysis (PCA) to organize those obtained from the algorithm, preserving some degree of similarity. To demonstrate the effectiveness of these methods, we interpreted two stratigraphic surfaces known as Maximum Transgressive Surface (MTS) and Maximum Regressive Surface (MRS), then extracted some attributes to run clustering experiments. Furthermore, we performed the principal component analysis and selected the first three components to be clustered. Subsequently, these components were used to organize the labels obtained with K-means through the two proposed techniques. Finally, we interpreted the outstanding results obtained from the methodologies proposed, allowing us to understand better seismic facies and the depositional environments over stratigraphic surfaces.
NSTL
Elsevier