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Interpretation of volcanic magnetic anomalies using differential search algorithm: case study from the Kula volcanic park, western Türkiye

Özyalın Şenol

Acta Geophysica

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2023

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Vol. 71, no. 3

1203--1224

EN

A differential search algorithm (DSA) application, which is a metaheuristic inspired by nature, for total field aeromagnetic data caused by volcanoes over a 2D dipping dyke is presented. Inversion of the total magnetic anomalies was performed by adding the background level in addition to the parameters of the dyke model (e.g., dip angle, the depth to the top, half-width, the distance from the origin to the reference point, and amplitude coefficient), which are often tried to be estimated in the literature studies. In synthetic dyke models, the efficiency of the DSA in parameter estimation of theoretically generated magnetic anomalies that do not contain noise and contain random noise at different levels has been demonstrated. Firstly, in the synthetic dyke model, the efficiency of the DSA in parameter estimation of theoretically generated noise-free magnetic anomaly is demonstrated. Additionally, different levels of random noise were added to the same synthetic model anomaly to test the performance of the algorithm in case the data contained noise. The results of the inversion show that the model parameters estimated from the DSA agree well with the correct ones. This fit was also statistically checked by calculating the probability density function. In the real case, the inversion approach was then used to interpret five prominent total aeromagnetic anomalies over the well-known Kula volcanic field located in western Türkiye. The depths and widths of these magmatic bodies lying underneath these volcanic cones are about 450 m and 470 m, respectively.

2

Interpretation of remote sensing and aeromagnetic data to depict the structural framework of the transitional zone between the Igarra Schist belt and Anambra Basin, Nigeria

Salawu Naheem Banji

Acta Geophysica

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2023

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Vol. 71, no. 1

227--246

EN

High-resolution aeromagnetic and Landsat-8 data were utilized for the structural investigation of the Igarra Schist Belt located where the Precambrian crystalline basement is unconformably overlain by the late-Cretaceous Anambra Basin fill. Analysis of the Landsat-8 data exhibits major lineaments that trend in E–W, ENE–WSW, NNW–SSE and N–S directions. Results from the analysis of total field anomaly data using total gradient amplitude and tilt angle of the horizontal gradient also show these same lineament trends. The superimposition of Landsat-8 and aeromagnetic data-derived lineaments resulted in the mapping of the regional lineaments, which provide clues to structurally controlled gold mineralization in the Igarra Schist Belt region. Details mapped from the remote sensing data show surface contacts that correspond to the boundary between the Igarra Schist Belt and Anambra Basin mapped from aeromagnetic data. The source parameter imaging of the aeromagnetic data provides depth estimates of the magnetic basement of the Igarra Schist Belt and Anambra Basin, which varies from 50 to above 650 m. The integration of the remote sensing and aeromagnetic lineaments with the 3-D Euler deconvolution results reveals that the locations of cluster solutions alignment with lineaments are target areas for gold mineralization, which is correlative to gold occurrences in the region.

3

Prediction of the electromagnetic responses of geological bodies based on a temporal convolutional network model

Yuan Chongxin, Wang Xuben, Deng Fei, Wang Kunpeng, Yang Rui

Acta Geophysica

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2022

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Vol. 70, no 1

191--209

EN

The transient electromagnetic method employed in aeromagnetic surveys has been widely used for geophysical, petroleum, and engineering exploration because geophysical characteristics can be predicted as an inversion problem based on measured electromagnetic response data. However, this process requires uniformly and densely distributed electromagnetic response data, which are typically unavailable in actual TEM applications due to the high cost of the aeromagnetic surveys, which necessitates the use of large grid patterns to effectively map large areas. Therefore, developing methods for predicting missing electromagnetic response data based on the available data is essential for ensuring the accurate characterization of geological bodies. The present work addresses this issue by establishing an electromagnetic response curve prediction model based on a temporal convolutional network (TCN) architecture. Firstly, the electromagnetic response data is subjected to grey relational analysis to obtain correlations and reduce the data dimension. Secondly, the response data with correlation degrees greater than a threshold are selected as TCN model input. Finally, the TCN model establishes the nonlinear relationship between the electromagnetic response parameter sequence and its output sequence. The proposed model and other existing state-of-the-art prediction models are applied to actual electromagnetic prospecting data, and the results demonstrate that the proposed TCN model provides higher prediction accuracy and stronger robustness than the other models considered. Moreover, the proposed model is suitable for processing multiple series of related data, such as electromagnetic response prediction models. Therefore, the proposed model has good application prospects in electromagnetic response prediction and electromagnetic response recovery research.

4

Crustal thickness and structural pattern evaluation of Sinai Peninsula using three-dimensional density modeling with aeromagnetic and earthquake data

Gaber Gaber M., Saleh Salah, Toni Mostafa

Acta Geophysica

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2022

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Vol. 70, no 2

639--657

EN

The Sinai Peninsula is a subplate located between the African and Arabian plates. It is an important subplate in the world; however, this region is poorly understood because of the shortage of geophysical data. Thus, this study focuses on built a three-dimensional (3D) high-resolution forward model of the crustal thickness with a new tectonic model and structural evaluation of the Sinai Peninsula to understand this area tectonically and determine its lithospheric and crustal thicknesses. Qualitative and quantitative interpretations of Bouguer gravity, reduced-to-the-pole (RTP) aeromagnetic, and earthquake data are explained to achieve the goals of this study. Two-dimensional (2D) interactive sequential modeling of gravity data is performed along with some well-selected profiles with existing crustal layer depth points from previous works in the studied region. Seventeen 2D models are constructed and used to determine the basement, Conrad (lower crust boundary), and Moho (upper mantle boundary) depths and to build a 3D model. Accuracy of the 3D built model is evaluated by extracting observed, calculated, and residual gravity anomaly maps. The results show that the basement rocks appear on the surface in the South of Sinai and deepen (down to 4.5 km) toward the North. The Conrad surface varies approximately from 16 km (in the northeast and southwest of Sinai) to 22.8 km (in the southeast). The Moho surface depth (i.e., crustal thickness) varies approximately from 28.8 to 34.2 km, and it deepens toward the northeastern and southwestern parts of Sinai. A tentative basement structure map is constructed from the horizontal gradient (H-gradient) filter and the 3D Euler deconvolution of the Bouguer gravity and RTP aeromagnetic data. Correlation between the geological background of the study area and the obtained results suggests that the Sinai Peninsula is tectonically active, mainly in its southern portion due to the tectonic movements along the Gulf of Suez and the Gulf of Aqaba. The crustal thickness increases southward and thins northward.

5

The magnetic response of hydrothermal alteration in iron-oxide basement complex, NW Nigeria

Aisabokhae Joseph Ehimare, Bamidele Oresajo

Geology, Geophysics and Environment

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2019

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Vol. 45, no. 2

145--156

EN

Aeromagnetic data was processed in order to delineate structural trends which may be indicative of potential gold mineral traps in the Watari hill gold prospect located between longitude 5°8''and 5°16'', and latitude 11°24'' and 11°30'' in Garin Hawal district, northwest Nigeria. Landsat-8 OLI data was processed to produce colour composite, band ratio and minimum noise fraction images that mapped the hydrothermal alteration zone in the study area. The multispectral images which were displayed in Red-Green-Blue colours were subsequently pan-sharpened to display a greater image resolution of the area. The application of enhancement algorithms such as an analytic signal to the aeromagnetic data over the alteration zone helped in mapping the mafic metavolcanics, felsic metasediments and intruding granitoid complexes. Further reductions using the second vertical derivative and tilt angle derivative filters aided in delineating fracture/faults and the contact zones of the formations, especially the metasediments-metavolcanic boundary that delineates the shear zone. This study showed that the low-angle geologic structure between the metasediments and metavolcanics where hydrothermal alteration is present is likely to accommodate veins of gold mineralization in the study area.