Three‐dimensional regularized focusing inversion of gravity gradient tensor component data

Geophysics ◽  
2004 ◽  
Vol 69 (4) ◽  
pp. 925-937 ◽  
Author(s):  
Michael S. Zhdanov ◽  
Robert Ellis ◽  
Souvik Mukherjee
Keyword(s):  
Local Density ◽  
Mineral Exploration ◽  
Gravity Data ◽  
Three Dimensional ◽  
Tensor Component ◽  
Airborne Gravity ◽  
Gravity Gradient ◽  
Gravity Method ◽  
Density Anomaly ◽  
And Inversion

We develop a new method for interpretation of tensor gravity field component data, based on regularized focusing inversion. The focusing inversion makes its possible to reconstruct a sharper image of the geological target than conventional maximum smoothness inversion. This new technique can be efficiently applied for the interpretation of gravity gradiometer data, which are sensitive to local density anomalies. The numerical modeling and inversion results show that the resolution of the gravity method can be improved significantly if we use tensor gravity data for interpretation. We also apply our method for inversion of the gradient gravity data collected by BHP Billiton over the Cannington Ag‐Pb‐Zn orebody in Queensland, Australia. The comparison with the drilling results demonstrates a remarkable correlation between the density anomaly reconstructed by the gravity gradient data and the true structure of the orebody. This result indicates that the emerging new geophysical technology of the airborne gravity gradient observations can improve significantly the practical effectiveness of the gravity method in mineral exploration.

scholarly journals Three-Dimensional Regularized Focusing Migration: A Case Study from the Yucheng Mining Area, Shandong, China

Minerals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 471
Author(s):  
Yidan Ding ◽  
Guoqing Ma ◽  
Shengqing Xiong ◽  
Haoran Wang
Keyword(s):  
Large Scale ◽  
Mineral Exploration ◽  
Gravity Data ◽  
Three Dimensional ◽  
Mining Area ◽  
Model Parameters ◽  
Step Size ◽  
Migration Direction ◽  
Migration Imaging ◽  
Imaging Results

Gravity migration is a fast imaging technique based on the migration concept to obtain subsurface density distribution. For higher resolution of migration imaging results, we propose a 3D regularized focusing migration method that implements migration imaging of an entire gravity survey with a focusing stabilizer based on regularization theory. When determining the model parameters, the iterative direction is chosen as the conjugate migration direction, and the step size is selected on the basis of the Wolfe–Powell conditions. The model tests demonstrate that the proposed method can improve the resolution and precision of imaging results, especially for blocky structures. At the same time, the method has high computational efficiency, which allows rapid imaging for large-scale gravity data. It also has high stability in noisy conditions. The developed novel method is applied to interpret gravity data collected from the skarn-type iron deposits in Yucheng, Shandong province. Migration results show that the depth of the buried iron ore in this area is 750–1500 m, which is consistent with the drilling data. We also provide recommendations for further mineral exploration in the survey area. This method can be used to complete rapid global imaging of large mining areas and it provides important technical support for exploration of deep, concealed deposits.

scholarly journals Bathymetry of Northwest Greenland Using “Ocean Melting Greenland” (OMG) High-Resolution Airborne Gravity and Other Data

2019 ◽  
Vol 11 (2) ◽  
pp. 131 ◽  
Author(s):  
Lu An ◽  
Eric Rignot ◽  
Romain Millan ◽  
Kirsty Tinto ◽  
Josh Willis
Keyword(s):  
High Resolution ◽  
Continental Shelf ◽  
Gravity Data ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Three Dimensions ◽  
Airborne Gravity ◽  
Lack Of Information ◽  
Sea Bed

Marine-terminating glaciers dominate the evolution of the Greenland Ice Sheet (GrIS) and its contribution to sea-level rise. Widespread glacier acceleration has been linked to the warming of ocean waters around the periphery of Greenland but a lack of information on the bathymetry of the continental shelf and glacial fjords has limited our ability to understand how subsurface, warm, salty ocean waters of Atlantic origin (AW) reach the glaciers and melt them from below. Here, we employ high-resolution, airborne gravity data (AIRGrav) in combination with multibeam echo sounding (MBES) data, to infer the bathymetry of the coastal areas of Northwest Greenland for NASA’s Ocean Melting Greenland (OMG) mission. High-resolution, AIRGrav data acquired on a 2 km spacing, 150 m ground clearance, with 1.5 mGal crossover error, is inverted in three dimensions to map the bathymetry. To constrain the inversion away from MBES data, we compare two methods: one based on the Direct Current (DC) shift of the gravity field (absolute minus observed gravity) and another based on the density of the bedrock. We evaluate and compare the two methods in areas with complete MBES coverage. We find the lowest standard error in bed elevation (±60 m) using the DC shift method. When applied to the entire coast of Northwest Greenland, the three-dimensional inversion reveals a complex network of connected sea bed channels, not known previously, that provide natural and varied pathways for AW to reach the glaciers across the continental shelf. The study demonstrates that the gravity approach offers an efficient and practical alternative to extensive ship mapping in ice-filled waters to obtain information critical to understanding and modeling ice-ocean interaction along ice sheet margins.

scholarly journals Identification of local sesars of tejakula buleleng bali with anomaly gravity data using second vertical derivative method

2020 ◽  
Vol 3 (1) ◽  
pp. 18-25
Author(s):  
Komang Ngurah Suarbawa ◽  
I Gusti Agung Putra Adnyana ◽  
Elvin Riyono
Keyword(s):  
Gravity Anomaly ◽  
Gravity Data ◽  
Three Dimensional ◽  
Fault Model ◽  
Two Dimensional ◽  
Upward Trend ◽  
Gravity Method ◽  
Vertical Derivative ◽  
Subsurface Structures ◽  
Derivative Method

Research has been carried out related to subsurface structures in the Tejakula Buleleng Bali area and its surroundings using the gravity method. This study aims to identify the local Tejakula fault. The data used in this study is gravity anomaly data obtained from observations of Geodetic Satellite (GEOSAT). The method used in interpreting the type of disturbance uses the Second Vertical Derivative method, which then produces two-dimensional (2D) and three-dimensional (3D) fault model interpretations. Based on the results obtained in the study, the condition of the bouguer gravity anomaly value in the Tejakula area and its surroundings at the research location is in the range of 65 mGal to 185 mGal. Meanwhile, based on the Second Vertical Derivative method in determining the type of fault, the Tejakula Fault can be categorized as a mandatory fault with an upward trend.

scholarly journals Sequential inversion of GOCE satellite gravity gradient data and terrestrial gravity data for the lithospheric density structure in the North China Craton

Solid Earth ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 1121-1144
Author(s):  
Yu Tian ◽  
Yong Wang
Keyword(s):  
North China ◽  
Gravity Data ◽  
Initial Density ◽  
Gravity Gradient ◽  
Density Structure ◽  
Satellite Gravity ◽  
Density Data ◽  
The North ◽  
Density Anomaly ◽  
Goce Satellite

Abstract. The North China Craton (NCC) is one of the oldest cratons in the world. Currently, the destruction mechanism and geodynamics of the NCC remain controversial. All of the proposed views regarding the issues involve studying the internal density structure of the NCC lithosphere. Gravity field data are among the most important data in regard to investigating the lithospheric density structure, and gravity gradient data and gravity data each possess their own advantages. Given the different observational plane heights between the on-orbit GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) satellite gravity gradient and terrestrial gravity and the effects of the initial density model on the inversion results, sequential inversion of the gravity gradient and gravity are divided into two integrated processes. By using the preconditioned conjugate gradient (PCG) inversion algorithm, the density data are calculated using the preprocessed corrected gravity anomaly data. Then, the newly obtained high-resolution density data are used as the initial density model, which can serve as constraints for the subsequent gravity gradient inversion. Several essential corrections are applied to the four gravity gradient tensors (Txx, Txz, Tyy, Tzz) of the GOCE satellite, after which the corrected gravity gradient anomalies (T′xx, T′xz, T′yy, T′zz) are used as observations. The lithospheric density distribution result within the depth range of 0–180 km in the NCC is obtained. This study clearly illustrates that GOCE data are helpful in understanding the geological settings and tectonic structures in the NCC with regional scale. The inversion results show that in the crust the eastern NCC is affected by lithospheric thinning with obvious local features. In the mantle, the presented obvious negative-density areas are mainly affected by the high-heat-flux environment. In the eastern NCC, the density anomaly in the Bohai Bay area is mostly attributed to the extension of the Tancheng–Lujiang major fault at the eastern boundary. In the western NCC, the crustal density anomaly distribution of the Qilian block is consistent with the northwest–southeast strike of the surface fault belt, whereas such an anomaly distribution experiences a clockwise rotation to a nearly north–south direction upon entering the mantle.

The problem of hollow space correction in subsurface gravity surveys

Geophysics ◽  
1983 ◽  
Vol 48 (10) ◽  
pp. 1406-1408
Author(s):  
B. V. Satyanarayana Murty ◽  
P. Chandra Reddy
Keyword(s):  
Mineral Exploration ◽  
Gravity Data ◽  
Surface Gravity ◽  
Gravity Method ◽  
Hollow Space ◽  
Additional Correction ◽  
Computational Work ◽  
Gravity Measurements

In spite of the extensive computational work involved in the reduction of data especially in estimating the effects of terrain, the gravity method has earned its own esteemed place in mineral exploration. Measurement of gravity in subsurface openings such as mine shafts, drives, and adits is much more valuable in mineral exploration and also useful in the planning, design, and maintenance of mines. However, because the anomalies being sought in this context are usually of very small magnitudes, accuracy at every stage of the gravity investigation is essential. Besides those corrections which are known for the surface gravity measurements, an additional correction for the subsurface gravity data is the result of hollow spaces.

Consistency investigation, vertical gravity estimation, and inversion of airborne gravity gradient data — A case study from northern Sweden

Geophysics ◽  
2016 ◽  
Vol 81 (3) ◽  
pp. B65-B76 ◽  
Author(s):  
Sayyed Mohammad Abtahi ◽  
Laust Börsting Pedersen ◽  
Jochen Kamm ◽  
Thomas Kalscheuer
Keyword(s):  
Scale Effects ◽  
Gravity Data ◽  
Airborne Gravity ◽  
Gravity Gradient ◽  
Small Scale ◽  
Northern Sweden ◽  
Data Set ◽  
Vertical Gravity ◽  
The Individual ◽  
Topographic Relief

For airborne gravity gradient data, it is a challenge to distinguish between high-frequency intrinsic and dynamically produced noise caused by the aircraft and small-scale effects from shallow density variations. To facilitate consistent interpretation, techniques that include all of the measured gravity gradient components are particularly promising. We represented the measurements by a common potential function accounting for lateral and height variations. Thus, it was possible to evaluate the internal consistency between the measured components and to identify components with bias or particularly strong noise. As an extra benefit for data sets that contain terrain-corrected and nonterrain-corrected gravity gradient measurements at flight altitude, we estimated terrain-corrected anomalies on the topographic relief using downward continuation and retrieved nonterrain-corrected gravity gradient data suitable for inversion using upward continuation. For a field data set from northern Sweden, the largest differences (up to 50 eotvos) between the measured and estimated components of the gravity gradient data were found in areas of high topographical relief. But the average residual standard deviations of the individual components were between 3.6 and 7.4 eotvos, indicating that the components were consistent in an average sense. We have determined the successful conversion of terrain-corrected airborne gravity gradient data to Bouguer gravity data on the topographic relief using ground-based vertical gravity data as a reference. A 3D inverse model computed from the nonterrain-corrected data clearly showed the depth extent of the geologic structures observed at the surface, but it only produced a weak representation of the shallow structure. In contrast, a 2D surface density model in which only lateral variations of density in the topographic relief was allowed exhibited more realistic density distributions in fair correlation with geology.

Historical development of the gravity method in exploration

Geophysics ◽  
2005 ◽  
Vol 70 (6) ◽  
pp. 63ND-89ND ◽  
Author(s):  
M. N. Nabighian ◽  
M. E. Ander ◽  
V. J. S. Grauch ◽  
R. O. Hansen ◽  
T. R. LaFehr ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Gravity Data ◽  
Low Cost ◽  
Dynamic Environment ◽  
Massive Sulfide ◽  
Airborne Gravity ◽  
Gravity Gradiometry ◽  
Positioning Systems ◽  
Gravity Method ◽  
Marine Gravity

The gravity method was the first geophysical technique to be used in oil and gas exploration. Despite being eclipsed by seismology, it has continued to be an important and sometimes crucial constraint in a number of exploration areas. In oil exploration the gravity method is particularly applicable in salt provinces, overthrust and foothills belts, underexplored basins, and targets of interest that underlie high-velocity zones. The gravity method is used frequently in mining applications to map subsurface geology and to directly calculate ore reserves for some massive sulfide orebodies. There is also a modest increase in the use of gravity techniques in specialized investigations for shallow targets. Gravimeters have undergone continuous improvement during the past 25 years, particularly in their ability to function in a dynamic environment. This and the advent of global positioning systems (GPS) have led to a marked improvement in the quality of marine gravity and have transformed airborne gravity from a regional technique to a prospect-level exploration tool that is particularly applicable in remote areas or transition zones that are otherwise inaccessible. Recently, moving-platform gravity gradiometers have become available and promise to play an important role in future exploration. Data reduction, filtering, and visualization, together with low-cost, powerful personal computers and color graphics, have transformed the interpretation of gravity data. The state of the art is illustrated with three case histories: 3D modeling of gravity data to map aquifers in the Albuquerque Basin, the use of marine gravity gradiometry combined with 3D seismic data to map salt keels in the Gulf of Mexico, and the use of airborne gravity gradiometry in exploration for kimberlites in Canada.

Reformulation of Parker–Oldenburg's method for Earth's spherical approximation

2020 ◽  
Vol 222 (2) ◽  
pp. 1046-1073
Author(s):  
Wenjin Chen ◽  
Robert Tenzer
Keyword(s):  
Gravity Field ◽  
Large Scale ◽  
Gravity Data ◽  
Spherical Approximation ◽  
Gravity Gradient ◽  
Global Studies ◽  
Forward Modelling ◽  
Density Interface ◽  
And Inversion ◽  
Interface Geometry

SUMMARY Parker–Oldenburg's method is perhaps the most commonly used technique to estimate the depth of density interface from gravity data. To account for large density variations reported, for instance, at the Moho interface, between the ocean seawater density and marine sediments, or between sediments and the underlying bedrock, some authors extended this method for variable density models. Parker–Oldenburg's method is suitable for local studies, given that a functional relationship between gravity data and interface geometry is derived for Earth's planar approximation. The application of this method in (large-scale) regional, continental or global studies is, however, practically restricted by errors due to disregarding Earth's sphericity. Parker–Oldenburg's method was, therefore, reformulated also for Earth's spherical approximation, but assuming only a uniform density. The importance of taking into consideration density heterogeneities at the interface becomes even more relevant in the context of (large-scale) regional or global studies. To address this issue, we generalize Parker–Oldenburg's method (defined for a spherical coordinate system) for the depth of heterogeneous density interface. Furthermore, we extend our definitions for gravity gradient data of which use in geoscience applications increased considerably, especially after launching the Gravity field and steady-state Ocean Circulation Explorer (GOCE) gravity-gradiometry satellite mission. For completeness, we also provide expressions for potential. The study provides the most complete review of Parker–Oldenburg's method in planar and spherical cases defined for potential, gravity and gravity gradient, while incorporating either uniform or heterogeneous density model at the interface. To improve a numerical efficiency of gravimetric forward modelling and inversion, described in terms of spherical harmonics of Earth's gravity field and interface geometry, we use the fast Fourier transform technique for spherical harmonic analysis and synthesis. The (newly derived) functional models are tested numerically. Our results over a (large-scale) regional study area confirm that the consideration of a global integration and Earth's sphericty improves results of a gravimetric forward modelling and inversion.

scholarly journals Ocean melting of the Zachariae Isstrøm and Nioghalvfjerdsfjorden glaciers, northeast Greenland

2020 ◽  
Vol 118 (2) ◽  
pp. e2015483118
Author(s):  
Lu An ◽  
Eric Rignot ◽  
Michael Wood ◽  
Josh K. Willis ◽  
Jérémie Mouginot ◽  
...  
Keyword(s):  
Gravity Data ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Ocean Model ◽  
Airborne Gravity ◽  
Intermediate Water ◽  
Grounding Line ◽  
Independent Observations ◽  
Global Sea Level ◽  
The Impact

Zachariae Isstrøm (ZI) and Nioghalvfjerdsfjorden (79N) are marine-terminating glaciers in northeast Greenland that hold an ice volume equivalent to a 1.1-m global sea level rise. ZI lost its floating ice shelf, sped up, retreated at 650 m/y, and experienced a 5-gigaton/y mass loss. Glacier 79N has been more stable despite its exposure to the same climate forcing. We analyze the impact of ocean thermal forcing on the glaciers. A three-dimensional inversion of airborne gravity data reveals an 800-m-deep, broad channel that allows subsurface, warm, Atlantic Intermediate Water (AIW) (+1.25○C) to reach the front of ZI via two sills at 350-m depth. Subsurface ocean temperature in that channel has warmed by 1.3±0.5○C since 1979. Using an ocean model, we calculate a rate of ice removal at the grounding line by the ocean that increased from 108 m/y to 185 m/y in 1979–2019. Observed ice thinning caused a retreat of its flotation line to increase from 105 m/y to 217 m/y, for a combined grounding line retreat of 13 km in 41 y that matches independent observations within 14%. In contrast, the limited access of AIW to 79N via a narrower passage yields lower grounded ice removal (53 m/y to 99 m/y) and thinning-induced retreat (27 m/y to 50 m/y) for a combined retreat of 4.4 km, also within 12% of observations. Ocean-induced removal of ice at the grounding line, modulated by bathymetric barriers, is therefore a main driver of ice sheet retreat, but it is not incorporated in most ice sheet models.

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