Journal articles on the topic '3D Gravity inversion with seismic constraint'
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1
Rashidifard, Mahtab, Jérémie Giraud, Mark Lindsay, Mark Jessell, and Vitaliy Ogarko. "Constraining 3D geometric gravity inversion with a 2D reflection seismic profile using a generalized level set approach: application to the eastern Yilgarn Craton." Solid Earth 12, no. 10 (October 22, 2021): 2387–406. http://dx.doi.org/10.5194/se-12-2387-2021.
Abstract:
Abstract. One of the main tasks in 3D geological modeling is the boundary parametrization of the subsurface from geological observations and geophysical inversions. Several approaches have been developed for geometric inversion and joint inversion of geophysical datasets. However, the robust, quantitative integration of models and datasets with different spatial coverage, resolution, and levels of sparsity remains challenging. One promising approach for recovering the boundary of the geological units is the utilization of a level set inversion method with potential field data. We focus on constraining 3D geometric gravity inversion with sparse lower-uncertainty information from a 2D seismic section. We use a level set approach to recover the geometry of geological bodies using two synthetic examples and data from the geologically complex Yamarna Terrane (Yilgarn Craton, Western Australia). In this study, a 2D seismic section has been used for constraining the location of rock unit boundaries being solved during the 3D gravity geometric inversion. The proposed work is the first we know of that automates the process of adding spatially distributed constraints to the 3D level set inversion. In many hard-rock geoscientific investigations, seismic data are sparse, and our results indicate that unit boundaries from gravity inversion can be much better constrained with seismic information even though they are sparsely distributed within the model. Thus, we conclude that it has the potential to bring the state of the art a step further towards building a 3D geological model incorporating several sources of information in similar regions of investigation.
2
Geng, Meixia, J. Kim Welford, Colin G. Farquharson, and Xiangyun Hu. "Gravity modeling for crustal-scale models of rifted continental margins using a constrained 3D inversion method." GEOPHYSICS 84, no. 4 (July 1, 2019): G25—G39. http://dx.doi.org/10.1190/geo2018-0134.1.
Abstract:
We have developed a new constrained inversion method that is based on a probabilistic approach for resolving crustal structure from regional gravity data. The smoothness of estimated structures is included in the inversion by using a model covariance matrix, and the sparse boundary information obtained from seismic data is incorporated in the inversion by using linear equality constraints. Moreover, constraints on the average anomalous densities expected for different crustal layers are applied instead of using a depth-weighting function. Bathymetric data and sediment thicknesses are included in the inversion by using an a priori model. Using the proposed method, model structures with sharp boundaries can be obtained while the existing boundary information and sparse seismic constraints are honored. We determine through a synthetic example and a real-world example that the proposed constrained inversion method is a valid tool for studying crustal-scale structures.
3
Yang, Bo, Zhan Liu, and Kaijun Xu. "Integrating multigeophysical data to improve structural imaging in the Dayangshu Basin." Interpretation 8, no. 4 (October 26, 2020): SS87—SS96. http://dx.doi.org/10.1190/int-2019-0263.1.
Abstract:
We have used the integrated interpretation of gravity, magnetotelluric (MT) data, and seismic data to improve the structural imaging of the Dayangshu Basin. The Dayangshu Basin is mainly composed of clastic and volcanic rocks. The logging data in the basin show different degrees of direct hydrocarbon indication, suggesting that the Dayangshu Basin has good potential for exploration. However, the widely distributed volcanic rocks attenuate seismic waves and lead to poor seismic imaging. Thus, the seismic signal is weak in the Ganhe Formation (K1g) and reliable seismic images cannot be obtained below that formation. MT data can accurately obtain images of deep structures because the resistivity of volcanic rocks is significantly higher than that of sedimentary rocks. Therefore, to obtain a more reliable geologic model, we combine the traditional 3D MT inversion result with logging and seismic data to establish an initial model. The 3D MT fuzzy constrained inversion (FCI) produces a more reliable geophysical model and geologically meaningful results. The resistivity model inverted from FCI shows that volcanic rocks are widely distributed in the Ganhe Formation, and the resistivity value of the lower section of the Longjiang Formation is greater than that of the upper section of the Longjiang Formation. Finally, the 3D gravity inversion with structural constraints from 3D MT FCI method was performed to improve the model resolution in depth and to highlight the density variations within the Jiufengshan Formation, which can further optimize the geologic model. We have determined how the effective integration of gravity, MT, and seismic data can improve the structural imaging of the Dayangshu Basin.
4
Ognev, Igor, Jörg Ebbing, and Peter Haas. "Crustal structure of the Volgo–Uralian subcraton revealed by inverse and forward gravity modelling." Solid Earth 13, no. 2 (March 2, 2022): 431–48. http://dx.doi.org/10.5194/se-13-431-2022.
Abstract:
Abstract. Volgo–Uralia is a Neoarchaean easternmost part of the East European craton. Recent seismic studies of the Volgo–Uralian region provided new insights into the crustal structure of this area. In this study, we combine satellite gravity and seismic data in a common workflow to perform a complex study of Volgo–Uralian crustal structure, which is useful for further basin analysis of the area. In this light, a new crustal model of the Volgo–Uralian subcraton is presented from a step-wise approach: (1) inverse gravity modelling followed by (2) 3D forward gravity modelling. First, inversion of the satellite gravity gradient data was applied to determine the Moho depth for the area. Density contrasts between crust and mantle were varied laterally according to the tectonic units present in the region, and the model is constrained by the available active seismic data. The Moho discontinuity obtained from the gravity inversion was consequently modified and complemented in order to define a complete 3D crustal model by adding information on the sedimentary cover, upper crust, lower crust, and lithospheric mantle layers in the process of forward gravity modelling, where both seismic and gravity constraints were respected. The obtained model shows crustal thickness variations from 32 to more than 55 km in certain areas. The thinnest crust with a thickness below 40 km is found beneath the Precaspian basin, which is covered by a thick sedimentary layer. The thickest crust is located underneath the Ural Mountains as well as in the centre of the Volgo–Uralian subcraton. In both areas the crustal thickness exceeds 50 km. At the same time, initial forward gravity modelling has shown a gravity misfit of ca. 95 mGal between the measured Bouguer gravity anomaly and the forward calculated gravity field in the central area of the Volgo–Uralian subcraton. This misfit was interpreted and modelled as a high-density lower crust, which possibly represents underplated material. Our preferred crustal model of the Volgo–Uralian subcraton respects the gravity and seismic constraints and reflects the main geological features of the region with Moho thickening in the cratons and under the Ural Mountains and thinning along the Palaeoproterozoic rifts, Precaspian sedimentary basin, and Pre-Urals foredeep.
5
HASSAN, Ahmed Gamal Mohamed, and Karam Samir Ibrahim FARAG. "Multi-stage 3D Gravity Inversion Scheme for Maximum Optimization of the Subsurface Basement Model at Gebel El-Zeit Basin, Southwestern Gulf-of-Suez, Egypt." NEWS of the Ural State Mining University, no. 4 (December 15, 2023): 19–39. http://dx.doi.org/10.21440/2307-2091-2023-4-19-39.
Abstract:
Relevance and purpose of the work. Due to its basement fault block pattern in the sedimentary basin, the Southwestern Gulf of Suez’s Gebel El-Zeit basin is one of Egypt’s most desirable hydrocarbon concessions. However, salt diapers in sedimentary layers have hindered seismic interpretations in this area, making it challenging to build a 3D central primary basinal structure. This study uses Bouguer gravity anomalies to input basement complex lateral density model assumptions to determine the optimal three-dimensional basement depth for the study area. Research methodology. Based on the concept of sequential 3D spectral layered-earth inversion approaches, through trials with the Oldenburg and other forward models, many forward optimization strategies and parameterization sequences with variable constraint parameter assumptions were used to regulate the inversion operations within a proposed three-stage gravity inversion scheme to identify the optimal depth-density solution with a minimal computational data misfit. This study statistically analyzes the basement’s relief and complicated lateral density distribution to determine the best parameters for a 3D depth-density model solution. Zero regional gravity offset and DC-shift, which forced the mean error to be zero, helped simulate the lateral density model’s best-possible constraining assumptions. Results and conclusions. Correlating depth data from many stratigraphical-control wells drilled in the inverted 3D basement model confirmed the basement relief optimality of the study area. Correlation analysis showed a good match between the predicted and measured depths, proving the resulting optimality of the basement complex’s lateral density distribution, minimizing the computational depth error to a minimal percentage.
6
Sampietro, Daniele, and Martina Capponi. "Seismic Constrained Gravity Inversion: A Reliable Tool to Improve Geophysical Models Away from Seismic Information." Geosciences 11, no. 11 (November 12, 2021): 467. http://dx.doi.org/10.3390/geosciences11110467.
Abstract:
The exploitation of gravity fields in order to retrieve information about subsurface geological structures is sometimes considered a second rank method, in favour of other geophysical methods, such as seismic, able to provide a high resolution detailed picture of the main geological horizons. Within the current work we prove, through a realistic synthetic case study, that the gravity field, thanks to the availability of freely of charge high resolution global models and to the improvements in the gravity inversion methods, can represent a valid and cheap tool to complete and enhance geophysical modelling of the Earth’s crust. Three tests were carried out: In the first one a simple two-layer problem was considered, while in tests two and three we considered two more realistic scenarios in which the availability on the study area of constraints derived from 3D or 2D seismic surveys were simulated. In all the considered test cases, in which we try to simulate real-life scenarios, the gravity field, inverted by means of an advanced Bayesian technique, was able to obtain a final solution closer to the (simulated) real model than the assumed a priori information, typically halving the uncertainties in the geometries of the main geological horizons with respect to the initial model.
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Preston, Leiph, Christian Poppeliers, and David J. Schodt. "Seismic Characterization of the Nevada National Security Site Using Joint Body Wave, Surface Wave, and Gravity Inversion." Bulletin of the Seismological Society of America 110, no. 1 (November 19, 2019): 110–26. http://dx.doi.org/10.1785/0120190151.
Abstract:
ABSTRACT As a part of the series of Source Physics Experiments (SPE) conducted on the Nevada National Security Site in southern Nevada, we have developed a local-to-regional scale seismic velocity model of the site and surrounding area. Accurate earth models are critical for modeling sources like the SPE to investigate the role of earth structure on the propagation and scattering of seismic waves. We combine seismic body waves, surface waves, and gravity data in a joint inversion procedure to solve for the optimal 3D seismic compressional and shear-wave velocity structures and earthquake locations subject to model smoothness constraints. Earthquakes, which are relocated as part of the inversion, provide P- and S-body-wave absolute and differential travel times. Active source experiments in the region augment this dataset with P-body-wave absolute times and surface-wave dispersion data. Dense ground-based gravity observations and surface-wave dispersion derived from ambient noise in the region fill in many areas where body-wave data are sparse. In general, the top 1–2 km of the surface is relatively poorly sampled by the body waves alone. However, the addition of gravity and surface waves to the body-wave dataset greatly enhances structural resolvability in the near surface. We discuss the methodology we developed for simultaneous inversion of these disparate data types and briefly describe results of the inversion in the context of previous work in the region.
8
Colombo, Daniele, Gary McNeice, Nickolas Raterman, Mike Zinger, Diego Rovetta, and Ernesto Sandoval Curiel. "Exploration beyond seismic: The role of electromagnetics and gravity gradiometry in deep water subsalt plays of the Red Sea." Interpretation 2, no. 3 (August 1, 2014): SH33—SH53. http://dx.doi.org/10.1190/int-2013-0149.1.
Abstract:
The Red Sea is characterized by thick salt sequences representing a seal for potential hydrocarbon accumulations within Tertiary formations deposited over deep basement structures. The Red Sea “salt” is characterized by halite concentrations embedded in layered evaporite sequences composed of evaporite and clastic lithologies. Salt complicates seismic exploration efforts in the Red Sea by generating vertical and lateral velocity variations that are difficult to estimate by seismic methods alone. In these conditions, the exploration challenges of independently imaging the subsalt section and provide enhanced velocity model building capabilities were addressed by a multigeophysics strategy involving marine electromagnetics (magnetotellurics and controlled source electromagnetics [CSEM]) and gravity gradiometry surveys colocated with wide azimuth seismic. Three-dimensional inversion of MT and CSEM is performed first with minimal a priori constraints and then by including variable amounts of interpretation in the starting models. The internal variations in the evaporitic overburden, the subsalt, and the basement structures are independently imaged by combined electromagnetic methods and confirmed by new drilling results. CSEM, in particular, provides unprecedented detail of the internal structures within the salt overburden while magnetotellurics provides excellent reconstruction of the base of salt and basement. Gravity gradiometry shows primary sensitivity to the basement and the corresponding 3D inversion provides density distributions structurally consistent with the resistivity volumes. The common-structure, multiparameter models obtained from 3D inversion deliver additional aid to seismic interpreters to further derisk exploration in the Red Sea and provide additional detail to depth imaging velocity models. The reciprocal consistency of the obtained results show promises for extending the work to more analytical integration with seismic such as provided by joint geophysical inversion.
9
Xu, Zhengwei, Rui Wang, Wei Xiong, Jian Wang, and Dian Wang. "3D hybrid imaging based on gravity migration and regularized focusing inversion to predict the Poyang Basin interface." GEOPHYSICS 86, no. 4 (July 1, 2021): G55—G67. http://dx.doi.org/10.1190/geo2020-0396.1.
Abstract:
Describing and understanding the basement relief of sedimentary basins is vital for oil and gas exploration. The traditional method to map an interface in each spatial direction is based on 3D modeling of gravity Bouguer anomalies with variable lateral and vertical density contrasts using a priori information derived from other types of geoscience data sets as constraints (e.g., well and/or seismic data). However, in the preexploration stage, vertical gravity [Formula: see text], which is sometimes the only available geophysical data, is typically used to recover smooth density contrast distributions under a generic set of constraints. Apparently, the use of the [Formula: see text] component is not sufficient to produce geologically reasonable interpretations with high resolution. To address this, we have developed a novel process of hybrid inversion, combining gravity migration and inversion using the same [Formula: see text] data set, to distinguish the complicated interface between basement and sedimentary basin rocks from a full-space inverted density distribution volume. First, a 3D-migrated model delineating the basic sedimentary basin structure is derived using a focusing gravity iterative migration method, where a priori information is not necessary. Subsequently, under the framework of the regularized focusing conjugate inversion algorithm, a high-resolution density contrast model is inverted for delineation of the basement boundary by integrating the 3D-migrated density model as a priori information. We examine the method using one synthetic example and a field data case, of which a transformed resolution density matrix is developed from logarithmic space to qualitatively evaluate the practical resolutions. The high resolution of the density distribution of the Cretaceous basement with a clear interface is achieved and verified by limited seismic data and strata markers in limited wells.
10
Carpenter, Chris. "Machine-Learning Method Determines Salt Structures From Gravity Data." Journal of Petroleum Technology 73, no. 02 (February 1, 2021): 70–71. http://dx.doi.org/10.2118/0221-0070-jpt.
Abstract:
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 201424, “Machine-Learning Method To Determine Salt Structures From Gravity Data,” by Jie Chen, Cara Schiek-Stewart, and Ligang Lu, Shell, et al., prepared for the 2020 SPE Annual Technical Conference and Exhibition, originally scheduled to be held in Denver, 5-7 October. The paper has not been peer reviewed. In the complete paper, the authors develop a machine-learning (ML) method to determine salt structures directly from gravity data. Based on a U-net deep neural network, the method maps the gravity downward continuation volume directly to a salt body mask volume, which is easily interpretable for an exploration geophysicist. The authors conclude that the ML-based method from gravity data complements seismic data processing and interpretation for subsurface exploration. Introduction In subsurface exploration, seismic is the dominant method used to reconstruct the underground image for geophysicists and geologists to locate possible hydrocarbon reservoirs. Seismic acquisition is carried out by human-induced sound waves (by airgun or vibrators) that are recorded, once reflected, on the surface. Through the iterative waveform inversion process, a subsurface image can be reconstructed for reservoir location and property determination. Nonseismic (gravity and magnetic-measurement) methods, on the other hand, are passive measurements and not intrusive to the environment. In gravity data acquisition, gravimeters measure the change in the gravitation-al field, which can be used to determine the density variation on the subsurface. Compared with seismic acquisition, gravity acquisition is cheaper and introduces a much smaller carbon footprint. Gravity data resolution is, in principle, worse than that of seismic. However, especially in areas of salt structures, gravity data provide a unique addition because the density contrast between salt and the surrounding sediments in-creases with depth, while the velocity contrast decreases with depth. Therefore, gravity data provide valuable additional constraints in salt delineation for interpretation and seismic processing. Recently, ML and deep-learning (DL) applications in hydrocarbon exploration have been studied extensively. The authors note developments such as use of ML/DL on seismic data noise attenuation, salt interpretation from seismic stack, least-square inversion, rock-facies classification, and 4D seismic in reservoir management. To the authors’ knowledge, no literature exists that explores use of ML on nonseismic data. The authors’ method can map the gravity downward continuation volume directly to a salt body mask (0/1 for nonsalt/salt) volume, which saves iterative effort of the conventional gravity inversion process and is easily interpretable for explorational geophysicists and geologists. Gravity Data Processing Raw gravity data are measured as a 2D Bouguer anomaly (the difference between measured gravity and theoretical gravity value) grid. The first step of gravity inversion is to perform a downward continuation calculation to generate a 3D volume so that the depth of the density anomaly can be estimated. The equivalent source technique is one of the more-stable downward continuation calculations and is a preferred method for making downward continued volumes used in in-field reference drilling.
11
Hassan, A. G. M., K. S. I. Farag, A. A. F. Aref, and A. L. Piskarev. "METHODS FOR 3D INVERSION OF GRAVITY DATA IN INDENTIFYING TECTONIC FACTORS CONTROLLING HYDROCARBON ACCUMULATIONS IN THE EL ZEIT BASIN AREA, SOUTHWESTERN GULF OF SUEZ, EGYPT." Geodynamics & Tectonophysics 15, no. 2 (April 19, 2024): 0751. http://dx.doi.org/10.5800/gt-2024-15-2-0751.
Abstract:
The Gebel EL-Zeit area in the southwestern Gulf of Suez, Egypt, is an area with a significant hydrocarbon potential in sedimentary basins, so that the three-stage inversion method was proposed for the Bouguer anomalies observed therein. Salt diapirs obscured the deep structure of the main central El-Zeit basin; hence, this method was implemented to overcome challenges in 3D seismic modeling. Our study included direct and inverse parameterization sequences that involved analyzing the inputs and outputs within trial-and-error initiations and inverse estimations to assess whether and how much the constraining parameters used in the calculations could achieve the intended aim. Data reduction, filtering, optimization, and constraint assumptions were used to determine the minimal set of density model parameters needed to set limits on the acceptable range of density contrasts that are required to study the basement depths, swells, troughs, faulting/folding and intra-sedimentary structures, and for direct modeling aimed at creating a simple model to save time. The thirteen constrained wells with a total depth ranging from shallow to deep were not involved in direct modeling but provided quality control over the graphical display of the inverse results for the entire study area. Moreover, many parameter constraints were inverted to regulate the way the calculated data are related to the model’s solution that allowed us to determine which inversion trial provided the best parameterization sequence and, therefore, yielded the most appropriate solution for the depth-density model which is approximating reality with a minimal computation error in the study area.
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Le Magoarou, Camille, Katja Hirsch, Clement Fleury, Remy Martin, Johana Ramirez-Bernal, and Philip Ball. "Integration of gravity, magnetic, and seismic data for subsalt modeling in the Northern Red Sea." Interpretation 9, no. 2 (April 21, 2021): T507—T521. http://dx.doi.org/10.1190/int-2019-0232.1.
Abstract:
Rifts and rifted passive margins are often associated with thick evaporite layers, which challenge seismic reflection imaging in the subsalt domain. This makes understanding the basin evolution and crustal architecture difficult. An integrative, multidisciplinary workflow has been developed using the exploration well, gravity and magnetics data, together with seismic reflection and refraction data sets to build a comprehensive 3D subsurface model of the Egyptian Red Sea. Using a 2D iterative workflow first, we have constructed cross sections using the available well penetrations and seismic refraction data as preliminary constraints. The 2D forward model uses regional gravity and magnetic data to investigate the regional crustal structure. The final models are refined using enhanced gravity and magnetic data and geologic interpretations. This process reduces uncertainties in basement interpretation and magmatic body identification. Euler depth estimates are used to point out the edges of high-susceptibility bodies. We achieved further refinement by initiating a 3D gravity inversion. The resultant 3D gravity model increases precision in crustal geometries and lateral density variations within the crust and the presalt sediments. Along the Egyptian margin, where data inputs are more robust, basement lows are observed and interpreted as basins. Basement lows correspond with thin crust ([Formula: see text]), indicating that the evolution of these basins is closely related to the thinning or necking process. In fact, the Egyptian Northern Red Sea is typified by dramatic crustal thinning or necking that is occurring over very short distances of approximately 30 km, very proximal to the present-day coastline. The integrated 2D and 3D modeling reveals the presence of high-density magnetic bodies that are located along the margin. The location of the present-day Zabargad transform fault zone is very well delineated in the computed crustal thickness maps, suggesting that it is associated with thin crust and shallow mantle.
13
Cella, Federico, Rosa Nappi, Valeria Paoletti, and Giovanni Florio. "Basement Mapping of the Fucino Basin in Central Italy by ITRESC Modeling of Gravity Data." Geosciences 11, no. 10 (September 22, 2021): 398. http://dx.doi.org/10.3390/geosciences11100398.
Abstract:
Sediments infilling in intermontane basins in areas with high seismic activity can strongly affect ground-shaking phenomena at the surface. Estimates of thickness and density distribution within these basin infills are crucial for ground motion amplification analysis, especially where demographic growth in human settlements has implied increasing seismic risk. We employed a 3D gravity modeling technique (ITerative RESCaling—ITRESC) to investigate the Fucino Basin (Apennines, central Italy), a half-graben basin in which intense seismic activity has recently occurred. For the first time in this region, a 3D model of the Meso-Cenozoic carbonate basement morphology was retrieved through the inversion of gravity data. Taking advantage of the ITRESC technique, (1) we were able to (1) perform an integration of geophysical and geological data constraints and (2) determine a density contrast function through a data-driven process. Thus, we avoided assuming a priori information. Finally, we provided a model that honored the gravity anomalies field by integrating many different kinds of depth constraints. Our results confirmed evidence from previous studies concerning the overall shape of the basin; however, we also highlighted several local discrepancies, such as: (a) the position of several fault lines, (b) the position of the main depocenter, and (c) the isopach map. We also pointed out the existence of a new, unknown fault, and of new features concerning known faults. All of these elements provided useful contributions to the study of the tectono-sedimentary evolution of the basin, as well as key information for assessing the local site-response effects, in terms of seismic hazards.
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Barnes, Gary, and Joseph Barraud. "Imaging geologic surfaces by inverting gravity gradient data with depth horizons." GEOPHYSICS 77, no. 1 (January 2012): G1—G11. http://dx.doi.org/10.1190/geo2011-0149.1.
Abstract:
The nonuniqueness problem that occurs when inverting potential field data is well known. It can, however, be surmounted by jointly inverting these data with independent data sets, incorporating depth information and regularizing the solution. The goal is to produce a geologic model that is compatible with all measured quantities, does not exceed any prescribed limits, and is geologically plausible. To achieve this, we have developed a spatially based surface inversion algorithm that solves for the geometric interface between geologic bodies. The bodies are constructed from grids of rectangular prisms that have their bottom depths adjusted by the algorithm to form the inverted surface. To solve large-scale inversions, approximations are used in the potential field calculations that allow internal matrices to be stored in sparse format with minimal loss of accuracy. The impetus for the work came from the need to combine airborne gravity gradient data with depth horizons estimated from interpreted 2D seismic profiles to form a high-resolution 3D inversion for imaging salt bodies. By treating the depth information as measurements rather than constraints, we accommodate uncertainties in these estimates. Total variation regularization is incorporated to support the sharp edges of the salt structures and to stabilize the solution. Inversions for near-surface structures also incorporate a high-pass filter to suppress the interference in the gravity gradient signal from deeper geology. The resulting optimization finds a surface that fits (in a least-squares sense) the depth information and the high-frequency content of the gravity gradient data.
15
Yang, Hai, Shengqing Xiong, Qiankun Liu, Fang Li, Zhiye Jia, Xue Yang, Haofei Yan, and Zhaoliang Li. "The crustal structure of the Longmenshan fault zone and its implications for seismogenesis: new insight from aeromagnetic and gravity data." Solid Earth 14, no. 12 (December 21, 2023): 1289–308. http://dx.doi.org/10.5194/se-14-1289-2023.
Abstract:
Abstract. Although many geophysical models have been proposed in the Longmenshan fault zone (LFZ) and its surrounding areas, the deep structure of the seismic gap and its constraint of the Wenchuan and Lushan earthquakes remain uncertain. Based on the compiled aeromagnetic data and Bouguer gravity data, we have tried to create a more detailed and reasonable magnetic and density model using 2D forward modeling and 3D inversion and made the deep structure of the LFZ visible. The research shows that structure is heterogenous across the LFZ. The earthquake epicenters are located in regions with high-magnetic anomalies and gravity gradients that are associated with rigid blocks that were likely to accumulate stress. However, the seismic gap shows low-magnetic anomalies and transition of gravity anomalies related to a weak zone. The Sichuan Basin has two NE-trending banded high-magnetic blocks extending beneath the LFZ that firmly support the idea that the crust of the Sichuan Basin has subducted downward the LFZ. More importantly, the basement subducts to approximately 33 km west of the Wenchuan–Maoxian fault, with a low dip angle beneath the middle segment of the LFZ, whereas the distance decreases to approximately 17 and 19 km under the southern segment. Thus, the crust of the Sichuan Basin beneath the middle segment extends farther than that beneath the southern segment, with the seismic gap as the transition zone. Therefore, we propose that the structural heterogeneity of the basement on the western margin of the Sichuan Basin may be the main reason for the different focal mechanisms and geodynamics of the Wenchuan and Lushan earthquakes.
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Malehmir, Alireza, Hans Thunehed, and Ari Tryggvason. "The Paleoproterozoic Kristineberg mining area, northern Sweden: Results from integrated 3D geophysical and geologic modeling, and implications for targeting ore deposits." GEOPHYSICS 74, no. 1 (January 2009): B9—B22. http://dx.doi.org/10.1190/1.3008053.
Abstract:
The Kristineberg mining area in the western part of the Paleoproterozoic Skellefte Ore District, northern Sweden, is well known for its base-metal and recent gold discoveries. A pilot 3D geologic model has been constructed on a crustal scale, covering an area of [Formula: see text] to depths of [Formula: see text]. Constrained 3D inverse and forward gravity modeling have been performed to confirm and refine previous modeling along seismic profiles using mainly 2.5D techniques. The 3D inverse gravity modeling was geared to generating isodensity surfaces that enclose regions within the model of anomalous density contrast. The 3D forward gravity modeling was conducted to include faulting and folding systems that are difficult to include in the inversion. The 3D geologic model supports many previous interpretations but also reveals new features of the regional geology that are important for future targeting of base-metal and gold deposits. The margins of a thick granite in the south dip steeply inward, suggesting the possibility of room to accommodate another large base-metal deposit if the granitic rocks are juxtaposed with volcanic rocks at depth. Gravity modeling also suggests the observed Bouguer gravity high within the western metasediments can be explained by a large mafic intrusion that has dioritic to tonalitic composition and no significant magnetic signature. Because mafic-ultramafic intrusions within metasediments can indicate gold, this interpretation suggests the western metasediments have a high gold potential.
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Krahenbuhl, Richard A., Cericia Martinez, Yaoguo Li, and Guy Flanagan. "Time-lapse monitoring of CO2 sequestration: A site investigation through integration of reservoir properties, seismic imaging, and borehole and surface gravity data." GEOPHYSICS 80, no. 2 (March 1, 2015): WA15—WA24. http://dx.doi.org/10.1190/geo2014-0198.1.
Abstract:
We have developed a feasibility study on the application of time-lapse gravity as a monitoring tool for a proposed [Formula: see text] sequestration test site. The results are a component of a larger geotechnical suitability study to evaluate a specific field’s potential for [Formula: see text] storage and to evaluate viable techniques for effective monitoring there. The reservoir model for this study was constructed from detailed reservoir data available through separate reservoir characterization studies of the field. The gravity inversion used was a highly constrained binary approach that incorporated reservoir geometry from seismic data and the internal 3D distributions of density change predicted from the reservoir engineering database. Incorporating borehole data for joint surface/borehole monitoring further improved the potential of time-lapse gravity to define [Formula: see text] movement during sequestration. In this paper, we present a subset of the entire study. Our results indicate that the site likely has a favorable combination of geometry, depth, thickness, and predicted density change from [Formula: see text] movement to be effectively monitored with surface time-lapse gravity.
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Ren, Zhengyong, and Thomas Kalscheuer. "Uncertainty and Resolution Analysis of 2D and 3D Inversion Models Computed from Geophysical Electromagnetic Data." Surveys in Geophysics 41, no. 1 (September 24, 2019): 47–112. http://dx.doi.org/10.1007/s10712-019-09567-3.
Abstract:
Abstract A meaningful solution to an inversion problem should be composed of the preferred inversion model and its uncertainty and resolution estimates. The model uncertainty estimate describes an equivalent model domain in which each model generates responses which fit the observed data to within a threshold value. The model resolution matrix measures to what extent the unknown true solution maps into the preferred solution. However, most current geophysical electromagnetic (also gravity, magnetic and seismic) inversion studies only offer the preferred inversion model and ignore model uncertainty and resolution estimates, which makes the reliability of the preferred inversion model questionable. This may be caused by the fact that the computation and analysis of an inversion model depend on multiple factors, such as the misfit or objective function, the accuracy of the forward solvers, data coverage and noise, values of trade-off parameters, the initial model, the reference model and the model constraints. Depending on the particular method selected, large computational costs ensue. In this review, we first try to cover linearised model analysis tools such as the sensitivity matrix, the model resolution matrix and the model covariance matrix also providing a partially nonlinear description of the equivalent model domain based on pseudo-hyperellipsoids. Linearised model analysis tools can offer quantitative measures. In particular, the model resolution and covariance matrices measure how far the preferred inversion model is from the true model and how uncertainty in the measurements maps into model uncertainty. We also cover nonlinear model analysis tools including changes to the preferred inversion model (nonlinear sensitivity tests), modifications of the data set (using bootstrap re-sampling and generalised cross-validation), modifications of data uncertainty, variations of model constraints (including changes to the trade-off parameter, reference model and matrix regularisation operator), the edgehog method, most-squares inversion and global searching algorithms. These nonlinear model analysis tools try to explore larger parts of the model domain than linearised model analysis and, hence, may assemble a more comprehensive equivalent model domain. Then, to overcome the bottleneck of computational cost in model analysis, we present several practical algorithms to accelerate the computation. Here, we emphasise linearised model analysis, as efficient computation of nonlinear model uncertainty and resolution estimates is mainly determined by fast forward and inversion solvers. In the last part of our review, we present applications of model analysis to models computed from individual and joint inversions of electromagnetic data; we also describe optimal survey design and inversion grid design as important applications of model analysis. The currently available model uncertainty and resolution analyses are mainly for 1D and 2D problems due to the limitations in computational cost. With significant enhancements of computing power, 3D model analyses are expected to be increasingly used and to help analyse and establish confidence in 3D inversion models.
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Vera, Naín, Carlos Couder-Castañeda, Jorge Hernández, Alfredo Trujillo-Alcántara, Mauricio Orozco-del-Castillo, and Carlos Ortiz-Aleman. "OpenMP Implementation of a Novel Potential-Field-Data Source-Growth-Based Inversion Approach for 3D Salt Imaging in Deepwater Gulf of Mexico." Applied Sciences 10, no. 14 (July 13, 2020): 4798. http://dx.doi.org/10.3390/app10144798.
Abstract:
Potential-field-data imaging of complex geological features in deepwater salt-tectonic regions in the Gulf of Mexico remains an open active research field. There is still a lack of resolution in seismic imaging methods below and in the surroundings of allochthonous salt bodies. In this work, we present a novel three-dimensional potential-field-data simultaneous inversion method for imaging of salt features. This new approach incorporates a growth algorithm for source estimation, which progressively recovers geological structures by exploring a constrained parameter space; restrictions are posed from a priori geological knowledge of the study area. The algorithm is tested with synthetic data corresponding to a real complex salt-tectonic geological setting commonly found in exploration areas of deepwater Gulf of Mexico. Due to the huge amount of data involved in three-dimensional inversion of potential field data, the use of parallel computing techniques becomes mandatory. In this sense, to alleviate computational burden, an easy to implement parallelization strategy for the inversion scheme through OpenMP directives is presented. The methodology was applied to invert and integrate gravity, magnetic and full tensor gradient data of the study area.
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Vallée, Marc A., Richard S. Smith, and Pierre Keating. "Metalliferous mining geophysics — State of the art after a decade in the new millennium." GEOPHYSICS 76, no. 4 (July 2011): W31—W50. http://dx.doi.org/10.1190/1.3587224.
Abstract:
Mining exploration was very active during the first decade of the twenty-first century because there were numerous advances in the science and technology that geophysicists were using for mineral exploration. Development came from different sources: instrumentation improvements, new numerical algorithms, and cross-fertilization with the seismic industry. In gravity, gradiometry kept its promise and is on the cusp of becoming a key technology for mining exploration. In potential-field methods in general, numerous techniques have been developed for automatic interpretation, and 3D inversion schemes came into frequent use. These inversions will have even greater use when geologic constraints can be applied easily. In airborne electromagnetic (EM) methods, the development of time-domain helicopter EM systems changed the industry. In parallel, improvements in EM modeling and interpretation occurred; in particular, the strengths and weaknesses of the various algorithms became better understood. Simpler imaging schemes came into standard use, whereas layered inversion seldom is used in the mining industry today. Improvements in ground EM methods were associated with the development of SQUID technology and distributed-acquisition systems; the latter also impacted ground induced-polarization (IP) methods. Developments in borehole geophysics for mining and exploration were numerous. Borehole logging to measure physical properties received significant interest. Perhaps one reason for that interest was the desire to develop links between geophysical and geologic results, which also is a topic of great importance to mining geologists and geophysicists.
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Gregersen, Ulrik, Paul C. Knutz, Henrik Nøhr-Hansen, Emma Sheldon, and John R. Hopper. "Tectonostratigraphy and evolution of the West Greenland continental margin." Bulletin of the Geological Society of Denmark 67 (July 27, 2020): 1–21. http://dx.doi.org/10.37570/bgsd-2019-67-01.
Abstract:
Large structural highs and sedimentary basins are identified from mapping of the West Greenland continental margin from the Labrador Sea to the Baffin Bay. We present a new tectonic elements map and a map of thickness from the seabed to the basement of the entire West Greenland margin. In addition, a new stratigraphic scheme of the main lithologies and tectonostratigraphy based on ties to all offshore exploration wells is presented together with seven interpreted seismic sections. The work is based on interpretation of more than 135 000 km of 2D seismic reflection data supported by other geophysical data, including gravity- and magnetic data and selected 3D seismic data, and is constrained by correlation to wells and seabed samples. Eight seismic mega-units (A–H) from the seabed to the basement, related to distinct tectonostratigraphic phases, were mapped. The oldest units include pre-rift basins that contain Proterozoic and Palaeozoic successions. Cretaceous syn-rift phases are characterised by development of large extensional fault blocks and basins with wedge-shaped units. The basin strata include Cretaceous and Palaeogene claystones, sandstones and conglomerates. During the latest Cretaceous, Paleocene and Eocene, crustal extension followed by oceanic crust formation took place, causing separation of the continental margins of Greenland and Canada with north-east to northward movement of Greenland. From Paleocene to Eocene, volcanic rocks dominated the central West Greenland continental margin and covered the Cretaceous basins. Development of the oceanic crust is associated with compressional tectonics and the development of strike-slip and thrust faults, pull-apart basins and inversion structures, most pronounced in the Davis Strait and Baffin Bay regions. During the late Cenozoic, tectonism diminished, though some intra-plate vertical adjustments occurred. The latest basin development was characterised by formation of thick Neogene to Quaternary marine successions including contourite drifts and glacial related shelf progradation towards the west and south-west.
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Rajeswaran, Dushyan, and Marcin Przywara. "The Great Australian Bight – from AVO prospectivity screening to potentially drillable targets in one of the world's remaining untapped basins." APPEA Journal 57, no. 2 (2017): 793. http://dx.doi.org/10.1071/aj16187.
Abstract:
The Ceduna Sub-basin in Australia’s southern margin offers an untapped opportunity for significant petroleum resource as part of the global exploration portfolio. Analogous to the prolific Niger delta in both size and structural style, this highly-extensional province contains up to 15 km of largely untested post-rift sediments including two widespread Late Cretaceous deltas linked to world-class oil-prone marine Cretaceous source rocks. Regional interpretation of legacy 2D seismic across the Bight Basin brings the sheer scale and structural complexity of this giant Cretaceous depocentre into perspective, but it is only through the detailed analysis of 8001 km2 of dual-sensor towed streamer 3D seismic that its true potential can be quantified. Rigorous phase and amplitude AVO QC of the pre-stack information, coupled with optimised velocity models fed into the depth migration sequence, have ensured amplitude fidelity and phase stability across all offset ranges. This has enabled a systematic and robust exploration workflow of AVO analysis and pre-stack inversion despite limited well data. Numerous dual-sensor case studies have nevertheless demonstrated these Relative Acoustic Impedance and Vp/Vs volumes to be reliably robust for prospect de-risking because of the extended low frequency bandwidth. Frontier screening supported by a partially-automated high-resolution stratigraphic framework has led to the identification of numerous prospects at multiple stratigraphic levels across the survey area. This includes isolation of laterally extensive and vertically amalgamated fan-like structures within the shallow Hammerhead delta using horizon-constrained high-definition spectral decomposition, and the extraction of potential AVO anomalies within the deeper structurally-controlled White Pointer sands draped across large gravity-driven listric growth faults.
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Sun, Siyuan, Changchun Yin, and Xiuhe Gao. "3D Gravity Inversion on Unstructured Grids." Applied Sciences 11, no. 2 (January 13, 2021): 722. http://dx.doi.org/10.3390/app11020722.
Abstract:
Compared with structured grids, unstructured grids are more flexible to model arbitrarily shaped structures. However, based on unstructured grids, gravity inversion results would be discontinuous and hollow because of cell volume and depth variations. To solve this problem, we first analyzed the gradient of objective function in gradient-based inversion methods, and a new gradient scheme of objective function is developed, which is a derivative with respect to weighted model parameters. The new gradient scheme can more effectively solve the problem with lacking depth resolution than the traditional inversions, and the improvement is not affected by the regularization parameters. Besides, an improved fuzzy c-means clustering combined with spatial constraints is developed to measure property distribution of inverted models in both spatial domain and parameter domain simultaneously. The new inversion method can yield a more internal continuous model, as it encourages cells and their adjacent cells to tend to the same property value. At last, the smooth constraint inversion, the focusing inversion, and the improved fuzzy c-means clustering inversion on unstructured grids are tested on synthetic and measured gravity data to compare and demonstrate the algorithms proposed in this paper.
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Liu, Jie, and Jianzhong Zhang. "Joint inversion of seismic slopes, traveltimes and gravity anomaly data based on structural similarity." Geophysical Journal International 229, no. 1 (November 26, 2021): 390–407. http://dx.doi.org/10.1093/gji/ggab478.
Abstract:
SUMMARY Attention is paid to joint inversion of multiple geophysical data because of its advantages on weakening the non-uniqueness of inversion and further enhancing comprehensive interpretation. Due to the good correlation between rock velocity and density, seismic and gravity data have been widely used in joint inversion. However, the joint inversion of pre-stack seismic reflection and gravity data remains underdeveloped at the exploration scale. Without a quantitive relation between velocity and density, we develop a structure-based joint inversion using seismic reflection traveltimes, slopes and Bouguer gravity anomaly data simultaneously for building both velocity and density models. In our method, cubic B-spline interpolation is used to parametrize the common knots of velocity and density models. Incorporating seismic slopes into the joint inversion framework, we build a composite objective function which minimizes the weighted-sum of seismic/gravity data misfits, regularization and structural constraint terms. By subdividing the knot spacing, a multiscale strategy is alternative to increase the stability of inversion. First, we describe the methodology, followed by three synthetic examples to illustrate the feasibility and benefits of the method. Examination of the convergence curves via inversion suggests that the desired solution is more likely to be obtained with gentle convergence of each term, thus it can be used as an indicator for weight adjustment. Additionally, locations of scattering points and acoustic impedance can be obtained as by-products. Compared with the inversion of the respective data, the joint inversion exhibits the complementary characteristics of seismic and gravity data, improves the distribution and structural features of the resulting physical properties, especially in deep and complex tectonic situations.
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Zhdanov, Michael S., Michael Jorgensen, and Le Wan. "Three-Dimensional Gravity Inversion in the Presence of the Sediment-Basement Interface: A Case Study in Utah, USA." Minerals 12, no. 4 (April 6, 2022): 448. http://dx.doi.org/10.3390/min12040448.
Abstract:
We introduce a novel approach to three-dimensional gravity inversion in the presence of the sediment-basement interface with a strong density contrast. This approach makes it possible to incorporate the known information about the basement depth in the inversion. It also allows the user to determine the depth-to-basement in the initial inversion phase. One can then use this interface to constrain the final inversion phase. First, the inversion generates the depth-to-basement model based on the 3D Cauchy-type integral representation of the gravity field. Then, in the second phase, full 3D voxel-type inversion applies the depth-to-basement model determined in the first phase as an a priori constraint. We use this approach to the 3D inversion of the Bouguer gravity anomaly data observed in Utah, USA. The results of inversion generated a 3D density model of the top layers of the earth’s crust, including unconsolidated sediments and the top of the crystalline basement.
26
Feng, Xuliang, Wanyin Wang, and Bingqiang Yuan. "3D gravity inversion of basement relief for a rift basin based on combined multinorm and normalized vertical derivative of the total horizontal derivative techniques." GEOPHYSICS 83, no. 5 (September 1, 2018): G107—G118. http://dx.doi.org/10.1190/geo2017-0678.1.
Abstract:
The basement of a rift sedimentary basin, often possessing smooth and nonsmooth shapes, is not easily recovered from gravity data by current inversion methods. We have developed a new 3D gravity inversion method to estimate the basement relief of a rift basin. In the inversion process, we have established the objective function by combining the gravity data misfit function, the known depth constraint function, and the model constraint function composed of the [Formula: see text]-norm and [Formula: see text]-norm, respectively. An edge recognition technology based on the normalized vertical derivative of the total horizontal derivative for gravity data is adopted to recognize the discontinuous and continuous parts of the basin and combine the two inputs to form the final model constraint function. The inversion is conducted by minimizing the objective function by the nonlinear conjugate gradient algorithm. We have developed two applications using synthetic gravity anomalies produced from two synthetic rift basins, one with a single graben and one with six differently sized grabens. The test results indicate that the inversion method is a feasible technique to delineate the basement relief of a rift basin. The inversion method is also tested on field data from the Xi’an depression in the middle of the Weihe Basin, Shaanxi Province, China, and the result illustrates its effectiveness.
27
Jiang, Wenbin. "3-D joint inversion of seismic waveform and airborne gravity gradiometry data." Geophysical Journal International 223, no. 2 (June 17, 2020): 746–64. http://dx.doi.org/10.1093/gji/ggaa296.
Abstract:
SUMMARY Seismic full waveform inversion (FWI) is a robust velocity model building technique for hydrocarbon exploration. However, the density reconstruction within the framework of multiparameter FWI leads to more degrees of freedom in the parametrization, and the sensitivity of the inversion change significantly from velocity to density, thereby increasing the ill-posedness of the inverse problem. Gravity gradiometry data inversion is an effective method for resolving density distribution. Combining gravity gradiometry data in FWI could alleviate the non-linearity of the inversion by contributing additional density information for the velocity model building. I develop a 3-D joint seismic waveform and gravity gradiometry inversion method for estimating the velocity and density distribution in the subsurface. The method alternatingly minimizes the waveform and gravity gradiometry misfit. The cross-gradient constraint is applied to enhance the structural similarity between the density and velocity models. The effectiveness of the joint inversion algorithm is demonstrated by a 3-D checkerboard model and 3-D SEAM model. Synthetic examples demonstrate that the joint inversion can improve the image quality in geologically complex areas. A case study from the South China Sea shows that the joint inversion improves the velocity and density solutions compared to a standalone seismic FWI. The joint inversion results are consistent with the pre-stack depth migration section and the shape of the salt body is well resolved.
28
Dai, Ronghuo, Fanchang Zhang, and Hanqing Liu. "Seismic inversion based on proximal objective function optimization algorithm." GEOPHYSICS 81, no. 5 (September 2016): R237—R246. http://dx.doi.org/10.1190/geo2014-0590.1.
Abstract:
Seismic impedance inversion has become a common approach in reservoir prediction. At present, the critical issue in the application of seismic inversion is its low computational efficiency, especially in 3D. To improve the computational efficiency, we have developed an inversion method derived from the proximal objective function optimization algorithm. Our inversion method calculates each unknown parameter in the model vector, one by one during iteration. Compared with routine gradient-dependent inversion algorithms, such as the iteratively reweighted least-squares (IRLS) algorithm, our inversion method has lower computational complexity as well as higher efficiency. In addition, to obtain a sparse reflectivity series, a long-tailed Cauchy distribution is used as the a priori constraint. The weak nonlinear problem owing to the introduction of Cauchy sparse constraint is addressed by taking advantage of reweighting strategy. Results of synthetic and real data tests illustrate that the proposed inversion method has higher computational efficiency than IRLS algorithm, and its inversion accuracy remains the same.
29
Zhdanov, Michael S., Le Wan, and Michael Jorgensen. "Joint Three-Dimensional Inversion of Gravity and Magnetic Data Collected in the Area of Victoria Mine, Nevada, Using the Gramian Constraints." Minerals 14, no. 3 (March 11, 2024): 292. http://dx.doi.org/10.3390/min14030292.
Abstract:
Gravity and magnetic surveys have been extensively employed in various fields like regional geology studies, environmental engineering, and mineral exploration. However, interpreting the data from these surveys remains a challenge because the potential field inversion lacks uniqueness. To address this issue, combining gravity and magnetic data in a joint inversion helps to narrow down the possible solutions. This study introduces a method for jointly inverting gravity and magnetic data, specifically focusing on the sediment–basement interface. Within this framework, a 3D voxel-type inversion using joint Gramian-based techniques incorporates a depth-to-basement model as a guiding constraint. This approach was applied to gravity and magnetic data collected around the Victoria Mine area in Nevada, USA. The joint inversion successfully produced 3D models representing the density and susceptibility of both unconsolidated sediments and the basement underlying the surveyed region.
30
Zhou, Shuai, Hongfa Jia, Tao Lin, Zhaofa Zeng, Ping Yu, and Jian Jiao. "An Accelerated Algorithm for 3D Inversion of Gravity Data Based on Improved Conjugate Gradient Method." Applied Sciences 13, no. 18 (September 13, 2023): 10265. http://dx.doi.org/10.3390/app131810265.
Abstract:
The 3D inversion algorithm for gravity data based on a smooth model constraint has been proven to yield a reasonable density distribution. However, as the amount of observed data and model parameters increases, the algorithm experiences issues with high memory consumption and prolonged computation time. Therefore, the corresponding problem in interpreting gravity inversion lies in developing a fast inversion algorithm. The conventional smooth model constraint inversion algorithm, based on regularization theory, requires the introduction of a model weighting function with a large matrix, and involves storage and operation of a large matrix with intermediate variables during inversion iteration, contributing significantly to the prolonged computation time. In this paper, a diagonal weight matrix is represented by vectorization, and the intermediate variable of the large matrix type in the iteration is replaced with the combination of a small matrix and a vector. Additionally, the algorithm flow of the conjugate gradient method is further optimized to minimize the number of vectors that need to be stored during iteration. As a result of these optimizations, the memory consumption of the algorithm during the operation process is successfully reduced. Finally, the experiments demonstrate the successful development of a fast 3D inversion algorithm for gravity data. Specifically, for a 80 × 80 × 20 mesh number inversion, our accelerated algorithm achieves an average speed of ~0.5 s per iteration, and the iterative process speeds up by a factor of 1000, providing an effective strategy for the fast inversion of large-scale data.
31
Nava-Flores, Mauricio, Carlos Ortiz-Aleman, Mauricio G. Orozco-del-Castillo, Jaime Urrutia-Fucugauchi, Alejandro Rodriguez-Castellanos, Carlos Couder-Castañeda, and Alfredo Trujillo-Alcantara. "3D Gravity Modeling of Complex Salt Features in the Southern Gulf of Mexico." International Journal of Geophysics 2016 (2016): 1–12. http://dx.doi.org/10.1155/2016/1702164.
Abstract:
We present a three-dimensional (3D) gravity modeling and inversion approach and its application to complex geological settings characterized by several allochthonous salt bodies embedded in terrigenous sediments. Synthetic gravity data were computed for 3D forward modeling of salt bodies interpreted from Prestack Depth Migration (PSDM) seismic images. Density contrasts for the salt bodies surrounded by sedimentary units are derived from density-compaction curves for the northern Gulf of Mexico’s oil exploration surveys. By integrating results from different shape- and depth-source estimation algorithms, we built an initial model for the gravity anomaly inversion. We then applied a numerically optimized 3D simulated annealing gravity inversion method. The inverted 3D density model successfully retrieves the synthetic salt body ensemble. Results highlight the significance of integrating high-resolution potential field data for salt and subsalt imaging in oil exploration.
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Li, Zelin, and Changli Yao. "An Investigation of lp-Norm Minimization for the Artifact-Free Inversion of Gravity Data." Remote Sensing 15, no. 14 (July 9, 2023): 3465. http://dx.doi.org/10.3390/rs15143465.
Abstract:
The l2-norm minimization is a common means for the 3D inversion of gravity data. The unconstrained l2-norm inversion will produce a smooth solution, which contains redundant structures and artifacts. Positivity-constrained l2-norm inversion can eliminate redundant structures and artifacts, resulting in a more reliable solution. However, the positivity constraint restricts the applications of gravity inversion to some extent because the measured gravity data are likely to be caused by both positive and negative sources. To address this issue, we propose a strategy that combines the lp-norm regularization and fine adjustment of the depth weighting function to refine the unconstrained gravity inversion results. Synthetic tests show that the proposed strategy yields an improved smooth solution compared with the unconstrained l2-norm inversion method. The proposed strategy is also applied to the inversion of gravity data collected over a Layikeleke iron–copper skarn deposit, Xinjiang, China.
33
Yuan, Sanyi, Shangxu Wang, Chunmei Luo, and Yanxiao He. "Simultaneous multitrace impedance inversion with transform-domain sparsity promotion." GEOPHYSICS 80, no. 2 (March 1, 2015): R71—R80. http://dx.doi.org/10.1190/geo2014-0065.1.
Abstract:
The impedance inversion technique plays a crucial role in seismic reservoir properties prediction. However, most existing impedance inversion methods often suffer from spatial discontinuities and instability because each vertical profile is processed independently in the inversion. We tested a transform-domain sparsity promotion simultaneous multitrace impedance inversion method to address this issue. The approach was implemented through minimizing a data misfit term and a transform-domain sparsity constraint term that incorporates the (2D or 3D) structural information into the inversion processing. A 2D synthetic data example was applied to mainly explain the roles of the transform-domain sparsity constraint. We determined that the transform-domain sparsity constraint can help in stabilizing the inversion, reducing the influence of high-wavenumber noise on the inverted result, and exploring spatial continuities of structures. Furthermore, a 3D field data example was used to examine the effectiveness of the proposed method for dealing with the real data and to reveal the difference between the results from the 3D simultaneous inversion and the section-by-section inversion. We found that the inverted results roughly matched a low-pass-filtered version of impedance curves derived from well log data. Also, it has been demonstrated that the 3D simultaneous inversion technique provided a better estimation than the section-by-section inversion technique in terms of guaranteeing more spatial continuities of geologic features in the impedance model.
34
Zhang, Junming, Deli Wang, Bin Hu, Xiangbo Gong, Yifei Chen, and Yang Zhang. "Multi-Shot Simultaneous Deghosting for Virtual-Shot Gathers via Integrated Sparse and Nuclear Norm Constraint Inversion." Remote Sensing 16, no. 12 (June 7, 2024): 2075. http://dx.doi.org/10.3390/rs16122075.
Abstract:
Seismic interferometry is a key technology in geophysical exploration, having achieved significant developments in constructing virtual seismic responses, overcoming the limitation of traditional exploration. However, non-physical reflections in virtual-shot gathers pose challenges for data processing and interpretation. This study focuses on deghosting in virtual-shot gather data processing. We propose a novel method that integrates sparse and nuclear norm constraint inversion for multi-shot simultaneous deghosting. Initially, a pseudo 3D data cube is created to enhance computational efficiency and lay the foundation for subsequent continuity regularization. Subsequently, an inversion framework is constructed to improve deghosting precision and stability by combining sparse and nuclear norm constraint inversion. Both synthetic and field examples demonstrate the superiority of our method, offering a new paradigm for virtual-shot gather data processing, and representing a major advancement in overcoming the inherent limitations of seismic interferometry.
35
Li, Yaoguo, and Chester J. Weiss. "Introduction to this special section: Potential fields." Leading Edge 41, no. 7 (July 2022): 452. http://dx.doi.org/10.1190/tle41070452.1.
Abstract:
This special section of The Leading Edge is dedicated to recent advances in potential field methods of geophysical exploration. In their broadest sense, these methods are rooted in data whose origins are compatible with solutions to the Laplace equation such as gravity, magnetics, and electrostatics, each responding to distinct and complementary material properties of the subsurface such as mass density, magnetic susceptibility, and electrical conductivity. These proxies for the real targets of geologic interest (lithologic boundaries, fluid-saturated zones, regions of mineral alteration, etc.) have proven themselves indispensable, for example, through joint inversion of seismic data and their direct reflection — no pun intended — of subsurface variations in seismic wavespeed. Indeed, joint inversion seismic and gravity data yield a direct path toward inference and constraint of the elastic moduli variations within the subsurface — variations that, themselves, can reveal changes in rock porosity or fracture density.
36
Bastos, B. Marcela S., and Vanderlei C. Oliveira Jr. "Isostatic constraint for 2D nonlinear gravity inversion on rifted margins." GEOPHYSICS 85, no. 1 (December 6, 2019): G17—G34. http://dx.doi.org/10.1190/geo2018-0772.1.
Abstract:
We have developed a nonlinear gravity inversion for simultaneously estimating the basement and Moho geometries, as well as the depth of the reference Moho along a profile crossing a passive rifted margin. To obtain stable solutions, we impose smoothness on basement and Moho, force them to be close to previously estimated depths along the profile and also impose local isostatic equilibrium. Different from previous methods, we evaluate the information of local isostatic equilibrium by imposing smoothness on the lithostatic stress exerted at depth. Our method delimits regions that deviate and those that can be considered in local isostatic equilibrium by varying the weight of the isostatic constraint along the profile. It also allows controlling the degree of equilibrium along the profile, so that the interpreter can obtain a set of candidate models that fit the observed data and exhibit different degrees of isostatic equilibrium. Our method also differs from earlier studies because it attempts to use isostasy for exploring (but not necessarily reducing) the inherent ambiguity of gravity methods. Tests with synthetic data illustrate the effect of our isostatic constraint on the estimated basement and Moho reliefs, especially at regions with pronounced crustal thinning, which are typical of passive volcanic margins. Results obtained by inverting satellite data over the Pelotas Basin, a passive volcanic margin in southern Brazil, agree with previous interpretations obtained independently by combining gravity, magnetic, and seismic data available to the petroleum industry. These results indicate that combined with a priori information, simple isostatic assumptions can be very useful for interpreting gravity data on passive rifted margins.
37
Wu, Guochao, Yue Wei, Siyuan Dong, Tao Zhang, Chunguo Yang, Linjiang Qin, and Qingsheng Guan. "Improved Gravity Inversion Method Based on Deep Learning with Physical Constraint and Its Application to the Airborne Gravity Data in East Antarctica." Remote Sensing 15, no. 20 (October 12, 2023): 4933. http://dx.doi.org/10.3390/rs15204933.
Abstract:
This paper aims to solve the limitations of traditional gravity physical property inversion methods such as insufficient depth resolution and difficulties in parameter selection, by proposing an improved 3D gravity inversion method based on deep learning. The deep learning network model is established using the fully convolutional U-net network. To enhance the generalization ability of the sample set, the large-scale training set and test set are generated by the random walk, based on the forward theory. Founded on the traditional loss function’s definition, this paper introduces an improvement incorporating a physical constraint to measure the degree of data fitting between the predicted and the real gravity data. This improvement significantly boosted the accuracy of the deep learning inversion method, as verified through both a single model and an intricate combination model. Finally, we applied this improved inversion method to the gravity data from the Gamburtsev Subglacial Mountains in the interior of East Antarctica, obtaining a comprehensive 3D crustal density structure. The results provide new evidence for the presence of a dense crustal root situated beneath the central Gamburtsev Province near the Gamburtsev Suture.
38
Song, Jiawen, Peiming Li, Zhongping Qian, Mugang Zhang, Pengyuan Sun, Wenchuang Wang, and Yuanming Ma. "Simultaneous vibroseis data separation through sparse inversion." Leading Edge 38, no. 8 (August 2019): 625–29. http://dx.doi.org/10.1190/tle38080625.1.
Abstract:
Compared with conventional seismic acquisition methods, simultaneous-source acquisition utilizes independent shooting that allows for source interference, which reduces the time and cost of acquisition. However, additional processing is required to separate the interfering sources. Here, we present an inversion-based deblending method, which distinguishes signal from blending noise based on coherency differences in 3D receiver gathers. We first transform the seismic data into the frequency-wavenumber-wavenumber domain and impose a sparse constraint to estimate the coherent signal. We then subtract the estimated signal from the original input to predict the interference noise. Driven by data residuals, the signal is updated iteratively with shrinking thresholds until the signal and noise fully separate. We test our presented method on two 3D field data sets to demonstrate how the method proficiently separates interfering vibroseis sources with high fidelity.
39
He, Haoyuan, Tonglin Li, and Rongzhe Zhang. "Joint Inversion of 3D Gravity and Magnetic Data under Undulating Terrain Based on Combined Hexahedral Grid." Remote Sensing 14, no. 18 (September 17, 2022): 4651. http://dx.doi.org/10.3390/rs14184651.
Abstract:
As an effective underground imaging method, the joint inversion of the gravity and magnetic data has an important application in the comprehensive interpretation of mineral exploration, and unstructured modeling is the key to accurately solving its topographic problem. However, the traditional tetrahedral grid can only impose the gradient-based constraints approximately, owing to its poor arrangement regularity. To address the difficulty of applying a cross-gradient constraint in an unstructured grid, we propose a joint inversion based on a combined hexahedral grid, which regularly divides the shallow part into curved hexahedrons and the deep part into regular hexahedrons. Instead of a cross-gradient in the spatial sense, we construct a geometric sense “cross-gradient” for a structural constraint to reduce the influence of approximation. In addition, we further correct the traditional sensitivity-based weighting function according to element volume, to make it suitable for an unstructured grid. Model tests indicate that the new grid can impose the cross-gradient constraint more strongly, and the proposed correction can effectively solve the false anomaly caused by the element volume difference. Finally, we apply our method to the measured data from a mining area in Huzhong, Heilongjiang Province, China, and successfully invert out the specific location of a known skarn deposit, which further proves its practicability.
40
Ma, Guoqing, Yifei Niu, Lili Li, Zongrui Li, and Qingfa Meng. "Adaptive Space–Location-Weighting Function Method for High-Precision Density Inversion of Gravity Data." Remote Sensing 15, no. 24 (December 15, 2023): 5737. http://dx.doi.org/10.3390/rs15245737.
Abstract:
Underground 3D density variation can be obtained via the inversion of gravity data, which is a very important basis for structural division, oil and gas structure definition, and mineral resource evaluation. A depth-weighting function is usually introduced as a structural constraint in density inversion to solve the skin effect. We propose an adaptive space–location-weighting (ASW) function for gravity field data to improve the resolution of the inversion, which adds the position and depth information provided by the DEXP method to form a new weighting function. The weighting function is partitioned according to the horizontal distribution of the source and can effectively improve the resolution of field sources with different positions and different depths. The results of model tests have shown that the ASW function method can significantly improve the precision and resolution of density inversion results and has good noise immunity. The ASW method was applied to interpret the real gravity data of a mining area in Shandong, and we speculated potential mineralization based on the inversion results, which corresponded well with the logging results.
41
Lelièvre, Peter G., Colin G. Farquharson, and Charles A. Hurich. "Joint inversion of seismic traveltimes and gravity data on unstructured grids with application to mineral exploration." GEOPHYSICS 77, no. 1 (January 2012): K1—K15. http://dx.doi.org/10.1190/geo2011-0154.1.
Abstract:
Seismic methods continue to receive interest for use in mineral exploration due to the much higher resolution potential of seismic data compared to the techniques traditionally used, namely, gravity, magnetics, resistivity, and electromagnetics. However, the complicated geology often encountered in hard-rock exploration can make data processing and interpretation difficult. Inverting seismic data jointly with a complementary data set can help overcome these difficulties and facilitate the construction of a common earth model. We considered the joint inversion of seismic first-arrival traveltimes and gravity data to recover causative slowness and density distributions. Our joint inversion algorithm differs from previous work by (1) incorporating a large suite of measures for coupling the two physical property models, (2) slowly increasing the effect of the coupling to help avoid potential convergence issues, and (3) automatically adjusting two Tikhonov tradeoff parameters to achieve a desired fit to both data sets. The coupling measures used are both compositional and structural in nature and allow the inclusion of explicitly known or implicitly assumed empirical relationships, physical property distribution information, and cross-gradient structural coupling. For any particular exploration scenario, the combination of coupling measures used should be guided by the geologic knowledge available. We performed our inversions on unstructured grids comprised of triangular cells in 2D, or tetrahedral cells in 3D, but the joint inversion methods are equally applicable to rectilinear grids. We tested our joint inversion methodology on scenarios based on the Voisey’s Bay massive sulfide deposit in Labrador, Canada. These scenarios present a challenge to the inversion of first-arrival traveltimes and we show how joint inversion with gravity data can improve recovery of the subsurface features.
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Mackie, Randall L., Max A. Meju, Federico Miorelli, Roger V. Miller, Carsten Scholl, and Ahmad Shahir Saleh. "Seismic image-guided 3D inversion of marine controlled-source electromagnetic and magnetotelluric data." Interpretation 8, no. 4 (July 23, 2020): SS1—SS13. http://dx.doi.org/10.1190/int-2019-0266.1.
Abstract:
Geologic interpretation of resistivity models from marine controlled-source electromagnetic (CSEM) and magnetotelluric (MT) data for hydrocarbon exploration and reservoir monitoring can be problematic due to structural complexity and low-resistivity contrasts in sedimentary units typically found in new frontier areas. It is desirable to reconstruct 3D resistivity structures that are consistent with seismic images and geologic expectations of the subsurface to reduce uncertainty in the evaluation of petroleum ventures. Structural similarity is achieved by promoting a cross-gradient constraint between external seismically derived gradient fields and the inversion resistivity model. The gradient fields come from coherency weighted structure tensors computed directly from the seismic volume. Consequently, structural similarity is obtained without the requirement for any horizon interpretation or picking, thus significantly reducing the complexity and effort. We have determined the effectiveness of this approach using CSEM, MT, and seismic data from a structurally complex fold-thrust belt in offshore northwest Borneo.
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Xu, Kaijun, and Yaoguo Li. "Integrated interpretation of gravity, magnetic, seismic, and well data to image volcanic units for oil-gas exploration in the eastern Junggar Basin, northwest China." Interpretation 8, no. 4 (November 1, 2020): SS113—SS127. http://dx.doi.org/10.1190/int-2019-0280.1.
Abstract:
We carried out a multigeophysical data joint interpretation to image volcanic units in an area where seismic imaging is difficult due to complicated and variable volcanic lithology. The gravity and magnetic methods can be effective in imaging the volcanic units because volcanic rocks are often strongly magnetic and have large density contrasts. Gravity and magnetic data have good lateral resolution, but they are faced with challenges in defining the depth extent. Although seismic data make for poor imaging in volcanic rocks, they can provide a reliable stratigraphic structure above volcanic rocks to improve the vertical resolution of the gravity and magnetic method. We have developed an integrated interpretation method that combines the advantages of seismic, gravity, magnetic, and well data to generate a 3D quasigeology model to image volcanic units. We first use seismic data to obtain the stratigraphic boundaries, and then we apply an anomaly stripping method based on a seismic-derived structure to extract residual gravity and magnetic anomaly produced by volcanic rocks. We further perform the 3D gravity and magnetic amplitude inversion to recover the distribution of the density and effective susceptibility. We perform geology differentiation using the inverted density and effective magnetic susceptibility to identify the spatial distribution of four groups of volcanic units. The results show that the integrated interpretation of multigeophysical data can significantly decrease the uncertainty associated with any single data set and yield more reliable imaging of lateral and vertical distribution of volcanic rocks.
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Barbosa, Valeria C., Paulo T. Menezes, and João B. Silva. "Gravity data as a tool for detecting faults: In-depth enhancement of subtle Almada’s basement faults, Brazil." GEOPHYSICS 72, no. 3 (May 2007): B59—B68. http://dx.doi.org/10.1190/1.2713226.
Abstract:
We demonstrate the potential of gravity data to detect and to locate in-depth subtle normal faults in the basement relief of a sedimentary basin. This demonstration is accomplished by inverting the gravity data with the constraint that the estimated basement relief presents local abrupt faults and is smooth elsewhere. We inverted the gravity data from the onshore Almada Basin in northeastern Brazil, and we mapped several normal faults whose locations and plane geometries were already known from seismic imaging. The inversion method delineated well both the discontinuities with small or large slips and a sequence of step faults. Using synthetic data, we performed a systematic search of normal fault slips versus fault displacement depths to map the fault-detectable region in this space. This mapping helps to assess the ability of gravity inversion to detect normal faults. Mapping shows that normal faults with small [Formula: see text], medium (about [Formula: see text]), and large (about [Formula: see text]) vertical slips can be detected if the maximum midpoint depths of the fault planes are smaller than 1.8, 3.8, and [Formula: see text], respectively.
45
Zhdanov, Michael S., Le Wan, Alexander Gribenko, Martin Čuma, Kerry Key, and Steven Constable. "Large-scale 3D inversion of marine magnetotelluric data: Case study from the Gemini prospect, Gulf of Mexico." GEOPHYSICS 76, no. 1 (January 2011): F77—F87. http://dx.doi.org/10.1190/1.3526299.
Abstract:
Three-dimensional magnetotelluric (MT) inversion is an emerging technique for offshore hydrocarbon exploration. We have developed a new approach to the 3D inversion of MT data, based on the integral equation method. The Tikhonov regularization and physical constraint have been used to obtain a stable and reasonable solution of the inverse problem. The method is implemented in a fully parallel computer code. We have applied the developed method and software for the inversion of marine MT data collected by the Scripps Institution of Oceanography (SIO) in the Gemini prospect, Gulf of Mexico. The inversion domain was discretized into 1.6 million cells. It took nine hours to complete 51 iterations on the 832-processor cluster with a final misfit between the observed and predicted data of 6.2%. The inversion results reveal a resistive salt structure, which is confirmed by a comparison with the seismic data. These inversion results demonstrate that resistive geoelectrical structures like salt domes can be mapped with reasonable accuracy using the 3D inversion of marine MT data.
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Roberts, Alan W., Richard W. Hobbs, Michael Goldstein, Max Moorkamp, Marion Jegen, and Bjørn Heincke. "Joint stochastic constraint of a large data set from a salt dome." GEOPHYSICS 81, no. 2 (March 1, 2016): ID1—ID24. http://dx.doi.org/10.1190/geo2015-0127.1.
Abstract:
Understanding the uncertainty associated with large joint geophysical surveys, such as 3D seismic, gravity, and magnetotelluric (MT) studies, is a challenge, conceptually and practically. By demonstrating the use of emulators, we have adopted a Monte Carlo forward screening scheme to globally test a prior model space for plausibility. This methodology means that the incorporation of all types of uncertainty is made conceptually straightforward, by designing an appropriate prior model space, upon which the results are dependent, from which to draw candidate models. We have tested the approach on a salt dome target, over which three data sets had been obtained; wide-angle seismic refraction, MT and gravity data. We have considered the data sets together using an empirically measured uncertain physical relationship connecting the three different model parameters: seismic velocity, density, and resistivity, and we have indicated the value of a joint approach, rather than considering individual parameter models. The results were probability density functions over the model parameters, together with a halite probability map. The emulators give a considerable speed advantage over running the full simulator codes, and we consider their use to have great potential in the development of geophysical statistical constraint methods.
47
Gao, Xiu-He, Sheng-Qing Xiong, Zhao-Fa Zeng, Chang-Chun Yu, Gui-Bin Zhang, and Si-Yuan Sun. "3D inversion modeling of joint gravity and magnetic data based on a sinusoidal correlation constraint." Applied Geophysics 16, no. 4 (December 2019): 519–29. http://dx.doi.org/10.1007/s11770-019-0792-z.
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Mu, Yang, John Castagna, and Gabriel Gil. "Application of sparse-layer inversion and harmonic bandwidth extension for a channel system in Southern Alberta, Canada." Interpretation 8, no. 2 (May 1, 2020): T217—T229. http://dx.doi.org/10.1190/int-2019-0027.1.
Abstract:
Sparse-layer reflectivity inversion decomposes a seismic trace into a limited number of simple layer responses and their corresponding reflection coefficients for top and base reflections. In contrast to sparse-spike inversion, the applied sparsity constraint is less biased against layer thickness and can thus better resolve thin subtuning layers. Application to a 3D seismic data set in Southern Alberta produces inverted impedances that have better temporal resolution and lateral stability and a less blocky appearance than sparse-spike inversion. Bandwidth extension harmonically extrapolated the frequency spectra of the inverted layers and nearly doubled the usable bandwidth. Although the prospective glauconitic sand tunes at approximately 37 m, bandwidth extension reduced the tuning thickness to 22 m. Bandwidth-extended data indicate a higher correlation with synthetic traces than the original seismic data and reveal features below the original tuning thickness. After bandwidth extension, the channel top and base are more evident on inline and crossline profiles. Lateral facies changes interpreted from the inverted acoustic impedance of the bandwidth-extended data are consistent with observations in wells.
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Karpiah, Arvin Boutik, Maxwell Azuka Meju, Roger Vernon Miller, Xavier Legrand, Prabal Shankar Das, and Raja Natasha Bt Raja Musafarudin. "Crustal structure and basement-cover relationship in the Dangerous Grounds, offshore North-West Borneo, from 3D joint CSEM and MT imaging." Interpretation 8, no. 4 (November 1, 2020): SS97—SS111. http://dx.doi.org/10.1190/int-2019-0261.1.
Abstract:
Accurate mapping of crustal thickness variations and the boundary relationships between sedimentary cover rocks and the crystalline basement is very important for heat-flow prediction and petroleum system modeling of a basin. Using legacy industry 3D data sets, we investigated the potential of 3D joint inversion of marine controlled-source electromagnetic (CSEM) and magnetotelluric (MT) data incorporating resistivity anisotropy to map these parameters across subbasins in the Dangerous Grounds in the southwestern rifted margin of the South China Sea, where limited previous seismic and potential field basement interpretations are available for comparison. We have reconstructed 3D horizontal and vertical resistivity models from the seabed down to [Formula: see text] depth for a [Formula: see text] area. The resistivity-versus-depth profile extracted from our 3D joint inversion models satisfactorily matched the resistivity and lithologic well logs at a wildcat exploration well location chosen for model validation. We found that the maximum resistivity gradients in the computed first derivative of the 3D resistivity volumes predict a depth to basement that matches the acoustic basement. The models predict the presence of 2 to approximately 5 km thick electrically conductive ([Formula: see text]) sedimentary cover atop an electrically resistive ([Formula: see text]) crystalline crust that is underlain by an electrically conductive ([Formula: see text]) upper mantle at depths that vary laterally from approximately 25 to 30 km below sea level in our study area. Our resistivity variation with depth is found to be remarkably consistent with the density distribution at Moho depth from recent independent 3D gravity/gradiometry inversion studies in this region. We suggest that 3D joint inversion of CSEM-MT, seismic, and potential field data is the way forward for understanding the deep structure of such rifted margins.
50
Martyshko, Petr, Igor Ladovskii, Denis Byzov, and Alexander Tsidaev. "Gravity Data Inversion with Method of Local Corrections for Finite Elements Models." Geosciences 8, no. 10 (October 10, 2018): 373. http://dx.doi.org/10.3390/geosciences8100373.
Abstract:
We present a new method for gravity data inversion for the linear problem (reconstruction of density distribution by given gravity field). This is an iteration algorithm based on the ideas of local minimization (also known as local corrections method). Unlike the gradient methods, it does not require a nonlinear minimization, is easier to implement and has better stability. The algorithm is based on the finite element method. The finite element approach in our study means that the medium (part of a lithosphere) is represented as a set of equal rectangular prisms, each with constant density. We also suggest a time-efficient optimization, which speeds up the inversion process. This optimization is applied on the gravity field calculation stage, which is a part of every inversion iteration. Its idea is to replace multiple calculations of the gravity field for all finite elements in all observation points with a pre-calculated set of uniform fields for all distances between finite element and observation point, which is possible for the current data set. Method is demonstrated on synthetic data and real-world cases. The case study area is located on the Timan-Pechora plate. This region is one of the promising oil- and gas-producing areas in Russia. Note that in this case we create a 3D density model using joint interpretation of seismic and gravity data.