Coastal Gravity Anomalies from Retracked Geosat/GM Altimetry: Improvement, Limitation and the Role of Airborne Gravity Data

The Earth’s potential information is important for exploration of the Earth’s gravity field. The techniques of measuring the Earth’s gravity using the terrestrial and ship borne technique are time consuming and have limitation on the vast area. With the space-based measuring technique, these limitations can be overcome. The satellite gravity missions such as Challenging Mini-satellite Payload (CHAMP), Gravity Recovery and Climate Experiment (GRACE), and Gravity-Field and Steady-State Ocean Circulation Explorer Mission (GOCE) has introduced a better way in providing the information on the Earth’s gravity field. From these satellite gravity missions, the Global Geopotential Models (GGMs) has been produced from the spherical harmonics coefficient data type. The information of the gravity anomaly can be used to predict the bathymetry because the gravity anomaly and bathymetry have relationships between each other. There are many GGMs that have been published and each of the models gives a different value of the Earth’s gravity field information. Therefore, this study is conducted to assess the most reliable GGM for the Malaysian Seas. This study covered the area of the marine area on the South China Sea at Sabah extent. Seven GGMs have been selected from the three satellite gravity missions. The gravity anomalies derived from the GGMs are compared with the airborne gravity anomaly, in order to figure out the correlation (R2) and the root mean square error (RMSE) of the data. From these assessments, the most suitable GGMs for the study area is GOCE model, GO_CONS_GCF_2_TIMR4 with the R2 and RMSE value of 0.7899 and 9.886 mGal, respectively. This selected model will be used in the estimating the bathymetry for Malaysian Seas in future.

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Study on Filtering Methods of Airborne Gravity

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.333-335.516 ◽

2013 ◽

Vol 333-335 ◽

pp. 516-521

Author(s):

Wei Zhou ◽

Ti Jing Cai

Keyword(s):

Impulse Response ◽

Finite Impulse Response ◽

Gravity Data ◽

Low Frequency ◽

Gravity Anomalies ◽

Window Function ◽

Airborne Gravity ◽

Infinite Impulse Response ◽

Kalman Smoothing ◽

Better Than

There are a great number of high-frequency and low-frequency noises in the airborne gravity data, so the filtering technology is needed to pick up the weak gravity anomaly. Based on the current filtering methods in airborne gravity data processing: butterworth infinite impulse response(IIR) filtering, window function finite impulse response(FIR) filtering and Kalman smoothing, several methods were compared and studied for the measured airborne gravity data, and the accuracies of extracted gravity anomalies were presented. Results show that the accuracy of Kalman smoothing is better than that of the combined filtering with butterworth IIR and window function FIR.

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Shallow vs. Deep Subsurface Structures of Central Luconia Province, Offshore Malaysia Reveal by Aeromagnetic, Airborne Gravity and Seismic Data

Applied Sciences ◽

10.3390/app11115095 ◽

2021 ◽

Vol 11 (11) ◽

pp. 5095

Author(s):

Siti Nur Fathiyah Jamaludin ◽

Manuel Pubellier ◽

Benjamin Sautter

Keyword(s):

Gravity Data ◽

Gravity Anomalies ◽

Airborne Gravity ◽

Deep Subsurface ◽

Southern Boundary ◽

Shallow Subsurface ◽

Subsurface Structures ◽

Crustal Block ◽

Central Luconia ◽

Seismic Lines

Across the Luconia continental shelf, the nature and structures of the crust are lacking geological understanding and precise characterization. Newly acquired, aeromagnetic, and airborne gravity data were used to assess deep and shallow sub-surface signals within the Central Luconia Province, off the coast of Sarawak, offshore Malaysia. Regional aeromagnetic anomalies appear to primarily reflect deep crustal features while depth (Z) tensors of airborne gravity anomalies evidence shallow subsurface structures. Strike directions of the interpreted structural trend on aeromagnetic and airborne gravity anomalies maps are measured and plotted into rose diagrams to distinguish the structural orientations for all datasets. Signature patterns extracted from the depth profiles were correlated with parallel seismic lines and nearest exploration wells and coincide well with the top of carbonate for Cycle IV/V and structures seen within the Cycle I and II sediments. The orientation of faults/lineaments at shallower depth is dominated by a NW-SE orientation, similar with the faults extracted from two recently published structural maps. Deeper subsurface sections yielded E-W to NWW-SEE dominant directions which were never presented in the published literature. The E-W oriented anomalies are postulated to represent the remnants of the accretion between the Luconia crustal block and southern boundary of the Palawan block. The NW-SE trend follows the same direction as prominent faults in the region. The insight into shallow and deep subsurface structures in Central Luconia Province imaged through airborne gravity and aeromagnetic data should provide guidelines and complementary information for regional structural studies for this area, particularly in combination with detailed seismic interpretation. Further evaluation on the response of Air-FTG® gravity and aeromagnetic could lead to the zonation of potential basement highs and hydrocarbon prospects in this area.

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Accuracy assessment of test flights using the Turnkey Airborne Gravity System over Alabama in 2008

Journal of Geodetic Science ◽

10.2478/jogs-2013-0018 ◽

2013 ◽

Vol 3 (2) ◽

pp. 136-142 ◽

Cited By ~ 1

Author(s):

Y.M. Wang ◽

S. Preaux ◽

T. Diehl ◽

V. Childers ◽

D. Roman ◽

...

Keyword(s):

Gravity Data ◽

Gravity Anomalies ◽

Gravity Models ◽

Surface Gravity ◽

Airborne Gravity ◽

National Geodetic Survey ◽

The Mean ◽

The Impact ◽

Gravity System ◽

Better Than

AbstractThe National Geodetic Survey (NGS) performed a few test flights using Micro-g’s Turnkey Airborne Gravity System (TAGS) at altitude of 1700, 6300 and 11000 meters over Alabama in 2008. The cross-track spacing was 10 km for the two lower flights and 5 km for the highest flight. The test flights not only provided important information regarding the precision and accuracy of the TAGS but also revealed the impact of flight altitudes and track spacing on the collected gravity data. The gravity anomalies at three altitudes were modeled using 3-dimensional Fourier series, then compared at the three altitudes. The agreement was excellent - the gravity anomalies agree with each other from 1.4 to 3.3 mGal RMS at the three altitudes. When the bias was removed, the agreement was improved to better than 1.1 mGal. On the ground (h =0), the three gravity models agree from 1.9 to 3.8 mGal RMS. After removing the mean, the agreement improved to better than 1.7 mGal. Similar results were obtained in comparison with recent surface gravity which was of sub-mGal accuracy. The overall agreement between the downward continued airborne gravity and the surface gravity was better than 1.7 mGal after removing the mean values.As expected, the flight altitude had a direct impact on accuracy of the values of gravity downward continued to the Earth’s surface. The comparisons with terrestrial gravity show that gravity collected at 11000 m is having an accuracy of ±3 mGal on the ground. This accuracy is slightly worse than the other two altitudes most probably due to smaller signal/noise ratios and larger downward continuation effects. The RMS values of differences between the downward continued airborne gravity at altitude 1700 and 6300 meters and the surface gravity are 2.0 and 1.6 mGals, respectively. Based on these comparisons, airborne gravity data collected at altitudes below 6300 meters should result in accuracy better than ±2 mGals on the ground. Note, however, that the test area is flat and the accuracy of airborne gravity would likely be worse in more rugged mountainous regions.

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Joint Gravity and Seismic Reflection Methods to Characterize the Deep Aquifers in Arid Ain El Beidha Plain (Central Tunisia, North Africa)

Water ◽

10.3390/w13091310 ◽

2021 ◽

Vol 13 (9) ◽

pp. 1310

Author(s):

Hajer Azaiez ◽

Hakim Gabtni ◽

Mourad Bédir

Keyword(s):

Seismic Reflection ◽

Large Scale ◽

Seismic Analysis ◽

Gravity Data ◽

Geophysical Methods ◽

Gravity Anomalies ◽

Integrated Approach ◽

Central Tunisia ◽

Deep Aquifers ◽

Advanced Analysis

Electric resistivity sounding and tomography, as well as electromagnetic sounding, are the classical methods frequently used for hydrogeological studies. In this work, we propose the development and implementation of an original integrated approach using the unconventional hydro–geophysical methods of gravity and seismic reflection for the fast, large–scale characterization of hydrogeological potential using the Ain El Beidha plain (central Tunisia) as an analogue. Extending the values of vintage petroleum seismic reflection profiles and gravity data, in conjunction with available geological and hydrogeological information, we performed an advanced analysis to characterize the geometry of deep tertiary (Oligocene and Eocene) aquifers in this arid area. Residual and tilt angle gravity maps revealed that most gravity anomalies have a short wavelength. The study area was mainly composed of three major areas: the Oued Ben Zitoun and Ain El Beidha basins, which are both related to negative gravity trends corresponding to low–density subsiding depocenters. These basins are separated by an important NE–SW trend called “El Gonna–J. El Mguataa–Kroumet Zemla” gravity high. Evaluation of the superposition of detected lineaments and Euler deconvolution solutions’ maps showed several NE–SW and N–S relay system faults. The 3D density inversion model using a lateral and vertical cutting plane suggested the presence of two different tectonic styles (thin VS thick). Results from the gravity analysis were in concordance with the seismic analysis. The deep Oligocene and Eocene seismic horizons were calibrated to the hydraulic wells and surrounding outcrops. Oligocene and Eocene geological reservoirs appear very fractured and compartmented. The faulting network also plays an important role in enhancing groundwater recharge process of the Oligocene and Eocene aquifers. Finally, generated isochron maps provided an excellent opportunity to develop future comprehensive exploration surveys over smaller and more favorable areas’ sub–basins.

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Study on Elliptic Filters in Airborne Gravity Data Processing

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.341-342.999 ◽

2013 ◽

Vol 341-342 ◽

pp. 999-1004

Author(s):

Wei Zhou ◽

Ti Jing Cai

Keyword(s):

Data Processing ◽

Gravity Data ◽

Airborne Gravity ◽

Optimal Parameters ◽

Evaluation Indicator ◽

Filter Order ◽

Upper Limit ◽

Optimal Value ◽

Low Pass ◽

Stopband Attenuation

For low-pass filtering of airborne gravity data processing, elliptic low-pass digital filters were designed and filtering influences of the elliptic filter order, upper limit passband frequency, maximal passband attenuation and minimal stopband attenuation were studied. The results show that the upper limit passband frequency has the greatest effect on filtering among four parameters; the filter order and the maximal passband attenuation have some influence, but instability will increase with larger order; the effect of the minimal stopband attenuation is not obvious when reaching a certain value, which requires a combination of evaluation indicator accuracy to determine the optimal value. The standard deviations of discrepancies between the elliptic filtered gravity anomaly with optimal parameters and the commercial software result are within 1mGal, and the internal accord accuracy along four survey lines after level adjusting is about 0.620mGal.

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Basin Depth Mapping Beneath Wellington City Based on Residual Gravity Anomalies

10.26686/wgtn.15176061 ◽

2021 ◽

Author(s):

◽

Alistair Stronach

Keyword(s):

Gravity Anomaly ◽

Sedimentary Basin ◽

Gravity Data ◽

Three Dimensional ◽

Maximum Amplitude ◽

Central Business District ◽

Gravity Anomalies ◽

Depth Map ◽

Capital City ◽

Detailed Knowledge

New Zealand’s capital city of Wellington lies in an area of high seismic risk, which is further increased by the sedimentary basin beneath the Central Business District (CBD). Ground motion data and damage patterns from the 2013 Cook Strait and 2016 Kaikōura earthquakes indicate that two- and three-dimensional amplification effects due to the Wellington sedimentary basin may be significant. These effects are not currently accounted for in the New Zealand Building Code. In order for this to be done, three-dimensional simulations of earthquake shaking need to be undertaken, which requires detailed knowledge of basin geometry. This is currently lacking, primarily because of a dearth of deep boreholes in the CBD area, particularly in Thorndon and Pipitea where sediment depths are estimated to be greatest. A new basin depth map for the Wellington CBD has been created by conducting a gravity survey using a modern Scintrex CG-6 gravity meter. Across the study area, 519 new high precision gravity measurements were made and a residual anomaly map created, showing a maximum amplitude anomaly of -6.2 mGal with uncertainties better than ±0.1 mGal. Thirteen two-dimensional geological profiles were modelled to fit the anomalies, then combined with existing borehole constraints to construct the basin depth map. Results indicate on average greater depths than in existing models, particularly in Pipitea where depths are interpreted to be as great as 450 m, a difference of 250 m. Within 1 km of shore depths are interpreted to increase further, to 600 m. The recently discovered basin bounding Aotea Fault is resolved in the gravity data, where the basement is offset by up to 13 m, gravity anomaly gradients up to 8 mGal/km are observed, and possible multiple fault strands identified. A secondary strand of the Wellington Fault is also identified in the north of Pipitea, where gravity anomaly gradients up to 18 mGal/km are observed.

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Basement Mapping of the Fucino Basin in Central Italy by ITRESC Modeling of Gravity Data

Geosciences ◽

10.3390/geosciences11100398 ◽

2021 ◽

Vol 11 (10) ◽

pp. 398

Author(s):

Federico Cella ◽

Rosa Nappi ◽

Valeria Paoletti ◽

Giovanni Florio

Keyword(s):

Seismic Activity ◽

Site Response ◽

Gravity Data ◽

A Priori ◽

Central Italy ◽

Gravity Anomalies ◽

Gravity Modeling ◽

Ground Shaking ◽

Sedimentary Evolution ◽

Fucino Basin

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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DETERMINATION AND MAPPING OF THE TERRESTRIAL GRAVITY ANOMALIES IN THE MOUNTAINOUS AREAS OF IRAQ

Journal of Information System and Technology Management ◽

10.35631/jistm.624021 ◽

2021 ◽

Vol 6 (24) ◽

pp. 213-225

Author(s):

Shazad Jamal Jalal ◽

Tajul Ariffin Musa ◽

Ami Hassan Md Din ◽

Wan Anom Wan Aris

Keyword(s):

Gravity Data ◽

Physical Geodesy ◽

Gravity Anomalies ◽

Gravity Survey ◽

Mountainous Areas ◽

Entire Study ◽

Terrestrial Gravity ◽

The Past ◽

Regional Gravity ◽

Entire Study Area

Gravity data and computing gravity anomalies are regarded as vital for both geophysics and physical geodesy fields. The mountainous areas of Iraq are characterized by the lack of regional gravity data because gravity surveys are rarely performed in the past four decades due to the Iraq-Iran war and the internal unstable political situation of this particular region. In addition, the formal map of the available terrestrial gravity which was published by the French Database of Bureau Gravimetrique International (International Gravimetric Bureau-in English) (BGI), introduces Iraq and the study area as a remote area and in white color because of the unavailability of gravity data. However, a dense and local (not regional) gravity data is available which was conducted by geophysics researchers 13 years ago. Therefore, the regional gravity survey of 160 gravity points was performed by the authors at an average 11 km apart, which was covers the whole area of Sulaymaniyah Governorate (part of the mountainous areas of Iraq). In spite of Although the risk of mine fields within the study area, suitable safe routes as well as a helicopter was used for the gravity survey of several points on the top of mountains. The survey was conducted via Lacoste and Romberg geodetic gravimeter and GPS handheld. The objective of the study is to determine and map the gravity anomalies for the entire study area, the data of which would assist different geosciences applications.

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Structural model of the Northern Latium volcanic area constrained by MT, gravity and aeromagnetic data

Annals of Geophysics ◽

10.4401/ag-3842 ◽

1997 ◽

Vol 40 (5) ◽

Author(s):

P. Capuano ◽

G. Florio ◽

P. Gasparini

Keyword(s):

Structural Model ◽

Gravity Data ◽

Gravity Anomalies ◽

Volcanic Area ◽

Aeromagnetic Data ◽

Geothermal Exploration ◽

Magnetotelluric Soundings ◽

Aeromagnetic Anomalies ◽

Deep Boreholes

The results of about 120 magnetotelluric soundings carried out in the Vulsini, Vico and Sabatini volcanic areas were modeled along with Bouguer and aeromagnetic anomalies to reconstruct a model of the structure of the shallow (less than 5 km of depth) crust. The interpretations were constrained by the information gathered from the deep boreholes drilled for geothermal exploration. MT and aeromagnetic anomalies allow the depth to the top of the sedimentary basement and the thickness of the volcanic layer to be inferred. Gravity anomalies are strongly affected by the variations of morphology of the top of the sedimentary basement, consisting of a Tertiary flysch, and of the interface with the underlying Mesozoic carbonates. Gravity data have also been used to extrapolate the thickness of the neogenic unit indicated by some boreholes. There is no evidence for other important density and susceptibility heterogeneities and deeper sources of magnetic and/or gravity anomalies in all the surveyed area.

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