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1

Appraisal of lineaments patterns and crustal architectures around the Owen fracture zone, Arabian Sea, using global gravity model data

Narayan Satya, Kumar Ujjawal, Sahoo Soumyashree Debasis, Pal Sanjit Kumar

Acta Geophysica

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2024

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Vol. 72, no. 1

29--48

EN

This study evaluates the efficacy of GECO gravity data for geophysical studies, mapping structural and tectonic features and their impact on gravity signatures in the study area. Computed correlation coefficient (96-98%), root-mean-square error (5.1-5.3 mGal), and standard deviation (3.9-4.2 mGal) between the GECO model-derived and ship-borne free-air gravity reveal the efficacy of the GECO gravity data for the geophysical studies in the region. A total horizontal derivative approach was used in order to enhance the residual and regional responses of the Bouguer gravity anomaly. The shorter-wavelength lineaments originated from subsurface mass heterogeneities were found trending in the northwest direction, subsequently east, north-northeast and east-northeast directions. In contrast, the longer-wavelength lineaments originating from deep-seated mass heterogeneities dominated in the east-northeast direction, followed by north-northeast and northwest directions. Lineaments occurring at shallower depths are associated with sedimentary/basement columns and could be utilised in basin demarcation for hydrocarbon exploration. In contrast, deep-seated lineaments originated due to deformities at the crust-mantle boundary or in the mantle and could be used in the region’s seismicity analysis. Spectral analysis and 2D forward modelling results indicate sediment thickness of ~ 2.0-6.0 km, basement thickness of ~ 6-14 km, and Moho depth of ~ 10-18 km. Delineated lineaments and computed basement and Moho depths were further validated with existing data. Anomalously high and low gravity features were interpreted based on Moho depth, basement thickness, and sediment thickness. This study concludes that anomalous gravity anomalies are mainly controlled by Moho topography despite the relatively thicker crust in the northern region. The crustal thickness mainly controls the southern latitude’s gravity signatures.

2

Structural features derived from a multi-method approach and 2.75D modelling of aeromagnetic data: a case study of the Pitoa–Figuil area (Northern Cameroon)

Kassia G. Voltaire Souga, Mbarga T. Ndougsa, Meying A., Ngoh J. Daniel, Embeng S. Ngoa

Acta Geophysica

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2023

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Vol. 71, no. 2

587--600

EN

An interpretation of aeromagnetic data was conducted in the Pitoa–Figuil area (Northern Cameroon). The aim of this investigation was the first to emphasise lineaments hidden under geological formations and secondly to propose two 2.75D models of the subsurface structures. Different magnetic data processing techniques were used, notably horizontal gradient magnitude, analytic signal and Euler deconvolution. The application of these techniques made it possible to map a certain number of lineaments representing discontinuities of magnetic susceptibility, mainly oriented NE–SW, NW–SE, E–W and ENE–WSW. The predominant direction for major lineaments is NE–SW and NW–SE. The major NE–SW trends have been attributed to the consequences of the Benue trough set-up due to the Atlantic opening. The lineaments map associated with the Euler solutions permits us to highlight and characterise 18 faults and some intrusive bodies. Euler solutions indicate depths down to 5.3 km for anomaly sources. The 2.75D modelling from the aeromagnetic anomaly reduced to the equator permits to understand the stratification of the deep and near-surface structures, which are sources of the observed anomalies. The sediment thickness values (3.5–4 km) combined with the presence of numerous deep faults make this area a potential site for hydrocarbon accumulations.

3

Analysis of recent airborne gravity and magnetic data for the interpretation of basement structures underneath the south–western Benue trough using source edge detector filters

Abdullahi Mukaila, Kumar Raj, Idi Bello Yusuf, Singh Upendra Kumar, Abba Adamu Usman

Acta Geophysica

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2023

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Vol. 71, no. 4

1595--1606

EN

We present the detail basement and trends of geological structures associated with the Mesozoic-Cenozoic volcanism in the south–western region of the Nigerian Benue trough using recent gravity and magnetic anomalies of the region. The analysis aimed at recognizing and mapping the basement structure that controlled the distribution and source host of hydrocarbon and other economic mineral resources in the region. The structural recognition and mapping is done on the basis of the utilization of the Tilt Angle (TA) and Total Horizontal Derivative of the Tilt Angle (THDTA) of gravity and magnetic data. From these techniques, we have been able to identify and mapped out those edges of anomalous sources due to the gravity and magnetic data that are in association with the basement geological structures of the area. Based on the mapped structural trends, it is observed that the basement structures derived from both the gravity and magnetic anomalies correlated well with the zones of volcanic rocks around Gboko and area between Lefin and Oturkpo. The two locations are sitting over gravity and magnetic highs suggesting high density and susceptibility material below the subsurface. The Euler deconvolution method suggested depths between 1 and 5 km from both gravity and magnetic data. Deeper basement of anomalous sources are suggested between 3 and 5 km. The 1 km depth interprets the regions of basement highs or corresponding to intrusive zones.

4

Study of gravity signature across the floating basement of Bundelkhand granite using 3D Euler deconvolution, source edge detection technique and various gravity gradient analyses

Ghosh Gopal K.

Acta Geophysica

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2022

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Vol. 70, no 4

1519--1537

EN

Bundelkhand granitic massif (BGM) encompasses various granitic plutonism in early Proterozoic age which contains granitic sample of massif within the age 2560±106 m.y. The Bundelkhand granitic massif is formed by various granitic upward intrusions. The gravity data suggest that it exhibits low gravity over the higher-gravity zone inside the Bundelkhand massif. It is suggested that due to the tectonic activity gravity variation takes place and the Bundelkhand granitic massif formed. Younger intrusive dykes, metasedimentary and gneissic rocks, older enclaves of metabasic, are supposed to be present in the zone. The present study has been carried the interpretation of gravity signature using various gravity gradient analyses of Bouguer gravity data in the Bundelkhand granitic belt which is one of the floating basement areas. The various gravity derivatives are analyzed, and it suggests about the source edge locations and the delineation pattern. Three-dimensional Euler deconvolution analysis has been carried out using specified structural index (SI) and different window sizes (WS). Apart from this, tilt derivative (Tilt), horizontal tilt derivative (TDX), analytical signal (ASA), total horizontal derivatives (THDR) and source edge detection (SED) have been studied. These various derived results are superimposed with one another map, and the results are correlated for understanding various lineament pattern including different strike and dip direction and different source depth locations. The integrated results look well correlated and provide value addition to get some geological consequences and better understanding the study area.

5

Delineation of major subsurface structural features and source depth locations using 3-D Euler deconvolution of gravity data at north-eastern part of India

Ghosh Gopal K.

Acta Geophysica

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2022

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Vol. 70, no 5

2033--2044

EN

The convergence of different major tectonic plates, namely the Eurasian, Indian and Sunda plates, may be the cause of the Assam Syntaxis due to the tectonic interaction between the Himalayan and the Indo-Burman ranges. The study covers the area between latitude 23°–28° N and longitude 88°–96° E and has experienced various types of earthquakes in the recent past. Seismic activity occurs in and around the Shillong Plateau, Mikir Hills, Arakan-Yoma Fold Belt, Naga Hills, parts of the Bengal Basin, lower and upper Brahmaputra valley, and the Mishmi Hills of the Himalayan foothills. Still, part of the study area is extremely unreachable and a limited number of thrust-faults have been identified from field geological studies and GIS maps received from the various sources. In this paper, an attempt has been made to study the delineation of thrust-fault locations using available ground gravity data of northeastern India with the help of a three-dimensional Euler deconvolution technique using the least squares method. Gravity data suggest an undulating nature throughout the area; however, high gravity values are observed at the Bengal Basin and Shillong Plateau, whereas lower gravity values are observed at Brahmaputra and Assam valley, Indo-Burman Range and Molasse Basin. The Shillong Plateau has high gravity with high elevation, whereas the Bengal Basin has high gravity with low elevation. This means that certain tectonic resettlement takes place in the Shillong Plateau, which causes the higher gravity anomaly. The use of Euler deconvolution with the help of a structural index plays a major role in gaining a better understanding of thrust-fault delineation and provides a mappable solution in this area. In this study, source depth estimation using 3- dimensional Euler deconvolution has been carried out by applying a range of structural index and window sizes. The different combinations of structural index and window size during the Euler deconvolution process generates several solutions including some unwanted spurious noise. To remove this noise, unrealistic solutions are discarded by applying filtering criteria to obtain the desired acceptable depth. The results derived using 3-dimensional Euler deconvolution correlate well with the previous finding of thrust-fault delineation. The present study validates the thrust-fault boundaries as well as providing additional thrust-fault settings in the complex tectonic area. The gravity data interpretation appears to offer a reasonable approach for source depth estimation and structural boundary identification.

6

Applying the Tilt depth and Tilt Euler techniques of gravity data to decipher the basement depth in Sichuan Basin, China

Chen Qing, Dong Yunpeng, Tan Xianfeng, Wang Jiabei, Huang Xiaoyu, Chen Hao

Acta Geophysica

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2021

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Vol. 69, no. 6

2173--2186

EN

The tilt angle (i.e., TDR) provides an efficient way to recognize the horizontal locations of multi-source geological bodies at different depths and inclination angles. The tilt-depth method was initially derived by applying magnetic formulas and used to calculate the depth of magnetic sources. Recently researchers have attempted to extend this method to interpret depths in gravity field data. The tilt-depth method of gravity anomalies (i.e., GTilt-depth) could capture the depth of a buried source effectively, which makes it superior at deciphering the basement relief. Meanwhile, Tilt-Euler deconvolution (i.e., Euler deconvolution of TDR) has been utilized for estimating a source’s position from gridded data automatically, which requires no structural index. However, analytical singularities can be produced when performing inversion with the Tilt-Euler deconvolution owning to the derivatives of TDR being incalculable when the horizontal derivative is zero. The improved Tilt-Euler deconvolution provided an efficient way to eliminate analytical singularities and obtain more stable solutions. The results from the theoretical model show that the GTilt-depth method and improved Tilt-Euler deconvolution could be applied to calculate the buried depths more accurately and effectively. Application of these methods shows that they are able to capture more detailed features, and provide more straightforward and accurate results of depth, than traditional methods. Furthermore, the results obtained from the gravity data in Sichuan Basin show that the basement depth ranges from 3 to 11 km, and 3 to 7 km in the central uplift, which contains a local depression with a depth of 8 km. The basement exhibits a general pattern of “shallow in middle and deep in east and west”, which is consistent with the results revealed by gravityseismic jointly interpreted profile. This research provides a better indication of the basement structure when interpreting the regional geology in Sichuan Basin.

7

Interpretation of Gravity Data using 3D Euler Deconvolution, Tilt Angle, Horizontal Tilt Angle and Source Edge Approximation of the North-West Himalaya

Ghosh G. K.

Acta Geophysica

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2016

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Vol. 64, no. 4

1112--1138

EN

The collision of the Indian plate and the Eurasian plate created shortening and imbrications with thrusting and faulting which influences northward tectonic movement. This plate movement has divided the Himalaya into four parts, viz. Outer Himalaya, Lesser Himalaya, Greater Himalaya, and Tethys Himalaya. The crystalline basement rock plays an imperative role for structural and tectonic association. The study has been carried out near Rishikesh-Badrinath neighborhood in the northwestern part of the Himalayan girdle with multifarious tectonic set up with thrusted and faulted geological setting. In this study area, 3D Euler deconvolution, horizontal gradient analysis, tilt angle (TILT) and horizontal tilt angle (TDX) analysis have been carried out using gravity data to delineate the subsurface geology and heterogeneity in the northwestern part of Himalaya. The Euler depth solutions suggest the source depth of about 12 km and various derivative analyses suggest the trend of the delineation thrust-fault boundaries along with the dip and strike direction in the study area.

8

3D Gravity Inversion using Tikhonov Regularization

Toushmalani R., Saibi H.

Acta Geophysica

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2015

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Vol. 63, no. 4

1044--1065

EN

Subsalt exploration for oil and gas is attractive in regions where 3D seismic depth-migration to recover the geometry of a salt base is difficult. Additional information to reduce the ambiguity in seismic images would be beneficial. Gravity data often serve these purposes in the petroleum industry. In this paper, the authors present an algorithm for a gravity inversion based on Tikhonov regularization and an automatically regularized solution process. They examined the 3D Euler deconvolution to extract the best anomaly source depth as a priori information to invert the gravity data and provided a synthetic example. Finally, they applied the gravity inversion to recently obtained gravity data from the Bandar Charak (Hormozgan, Iran) to identify its subsurface density structure. Their model showed the 3D shape of salt dome in this region.