scholarly journals New Bouguer Gravity Maps of Venezuela: Representation and Analysis of Free-Air and Bouguer Anomalies with Emphasis on Spectral Analyses and Elastic Thickness

2012 ◽  
Vol 2012 ◽  
pp. 1-15 ◽  
Author(s):  
Javier Sanchez-Rojas
Keyword(s):  
Gravity Data ◽  
Bouguer Anomaly ◽  
Geodetic Reference System ◽  
Bouguer Gravity ◽  
Free Air ◽  
Data Compilation ◽  
Regional Tectonic ◽  
Moho Depths ◽  
Free Air Anomaly ◽  
Gravity Map

A new gravity data compilation for Venezuela was processed and homogenized. Gravity was measured in reference to the International Gravity Standardization Net 1971, and the complete Bouguer anomaly was calculated by using the Geodetic Reference System 1980 and 2.67 Mg/m3. A regional gravity map was computed by removing wavelengths higher than 200 km from the Bouguer anomaly. After the anomaly separation, regional and residual Bouguer gravity fields were then critically discussed in term of the regional tectonic features. Results were compared with the previous geological and tectonic information obtained from former studies. Gravity and topography data in the spectral domain were used to examine the elastic thickness and depths of the structures of the causative measured anomaly. According to the power spectrum analysis results of the gravity data, the averaged Moho depths for the massif, plains, and mountainous areas in Venezuela are 42, 35, and 40 km, respectively. The averaged admittance function computed from the topography and Free-Air anomaly profiles across Mérida Andes showed a good fit for a regional compensation model with an effective elastic thickness of 15 km.

scholarly journals Gravity Study using Multi-2.5D Modeling and 3D Presentation for Al Ma'aniyah Depression, Southwest of Iraq

2021 ◽  
Vol 54 (2D) ◽  
pp. 113-124
Author(s):  
Ali M. Al-Rahim
Keyword(s):  
Gravity Data ◽  
Depth Map ◽  
Bouguer Gravity ◽  
Free Air ◽  
Exact Boundary ◽  
Power Spectrum Method ◽  
Basement Depth ◽  
3D Presentation ◽  
Free Air Gravity ◽  
Gravity Map

Tectonic depression area within and/or beside widespread basin is regarded as an important location for sub-basin sedimentary sequence of Iraq which may represent an excellent accumulation of bounded sediments. Al-Ma'aniyah depression, southwest Iraq is one of such type of sub-basin. Free-air gravity data show a NS extend of this depression inside Saudi Arabia. This work focuses on studying and multi-2.5D model creation for the depression in the Iraqi territory part using Bouguer gravity data and mapping its basement relief. Firstly, the exact boundary of the depression was outlined utilizing the Free-Air gravity data. Then, a precise selection of regional field for the study area was determined by using the power spectrum method, which accordingly defines the residual anomalies that could represent structural enclosures. Many positive anomalies were assigned and enhanced using vertical and total horizontal derivatives, where they were interpreted as basement-related features. Subsequently, a 2.5D multi modeling and depth inversion for the Bouguer gravity data were accomplished by converting the gravity map to a stacked profiles depth map. A nineteen gravity profiles, which cover the study area, were modeled by assuming 2D intra-sedimentary bodies. These bodies were best presented by a 3D view that clarifies the nature of the subsurface modeled structures. The modeling shows an extra density at the northern part of the depression, in contrast, it suggests low density bodies at its southern part, the case that appears inconsistent with a previously performed magnetic interpretation. The inversion of gravity data shows that the basement depth at Al-Ma'aniyah depression ranges from 7.5 to10 km.

Airborne gravity measurements over mountainous areas by using a LaCoste & Romberg air‐sea gravity meter

Geophysics ◽  
2002 ◽  
Vol 67 (3) ◽  
pp. 807-816 ◽  
Author(s):  
Jérôme Verdun ◽  
Roger Bayer ◽  
Emile E. Klingelé ◽  
Marc Cocard ◽  
Alain Geiger ◽  
...  
Keyword(s):  
Data Reduction ◽  
Classical Method ◽  
Gravity Data ◽  
Airborne Gravity ◽  
Mountainous Area ◽  
Vertical Acceleration ◽  
Mountainous Areas ◽  
Free Air ◽  
Gravity Measurements ◽  
Free Air Anomaly

This paper introduces a new approach to airborne gravity data reduction well‐suited for surveys flown at high altitude with respect to gravity sources (mountainous areas). Classical technique is reviewed and illustrated in taking advantage of airborne gravity measurements performed over the western French Alps by using a LaCoste & Romberg air‐sea gravity meter. The part of nongravitational vertical accelerations correlated with gravity meter measurements are investigated with the help of coherence spectra. Beam velocity has proved to be strikingly correlated with vertical acceleration of the aircraft. This finding is theoretically argued by solving the equation of the gravimetric system (gravity meter and stabilized platform). The transfer function of the system is derived, and a new formulation of airborne gravity data reduction, which takes care of the sensitive response of spring tension to observable gravity field wavelengths, is given. The resulting gravity signal exhibits a residual noise caused by electronic devices and short‐wavelength Eötvös effects. The use of dedicated exponential filters gives us a way to eliminate these high‐frequency effects. Examples of the resulting free‐air anomaly at 5100‐m altitude along one particular profile are given and compared with free‐air anomaly deduced from the classical method for processing airborne gravity data, and with upward‐continued ground gravity data. The well‐known trade‐off between accuracy and resolution is discussed in the context of a mountainous area.

Processing steps for the compiling AAGRG gravity maps

2020 ◽  
Author(s):  
Pavol Zahorec ◽  
Juraj Papčo ◽  
Roman Pašteka ◽  
Keyword(s):  
Gravity Data ◽  
Atmospheric Correction ◽  
Bouguer Anomaly ◽  
Taylor Series Expansion ◽  
Methodological Innovation ◽  
Atmospheric Effect ◽  
Free Air ◽  
Point Data ◽  
Anomaly Map ◽  
Bouguer Anomaly Map

<p>First unified complete Bouguer anomaly map of AlpArray area compiled from terrestrial gravity data is in preparation. The following steps to calculate the first version of the map were performed: 1. unification of different spatial, height and gravity systems, 2. getting available detailed (mainly LiDAR-based) elevation models and their transformation from physical to ellipsoidal heights, 3. calculation of mass corrections (gravity effect of the topography between the surface and ellipsoid level) with density 2 670 kg/m<sup>3</sup>, 4. calculation of bathymetric corrections for water masses below the ellipsoid (correction density -1 640 kg/m<sup>3</sup>), 5. calculation of lake correction for great alpine lakes (correction density -1 670 kg/m<sup>3</sup>), 6. calculation of the final complete Bouguer anomalies based on normal field (Somigliana formula with GRS80 parameters, free-air correction using Taylor series expansion to the 2<sup>nd</sup> order) and particular corrections including also the atmospheric correction.</p><p>The quality control of input data was performed based on the height differences between the point data and particular elevation models. Several thousand points with height residuals higher than chosen threshold (±50 m) were excluded. The available detailed local elevation models (resolution 10 – 20 m) were compared with global model MERIT (resolution 25 m).</p><p>The most significant methodological innovation is the ellipsoidal heights concept using straightforward calculation of mass/bathymetric corrections in respect to the ellipsoid instead of using the geophysical indirect effect computation. Our specially developed program Toposk was used for mass/bathymetric correction calculation (the standard distance of 166.7 km was used for the first version of the map) as well as for the calculation of lake corrections. Mass corrections amount to hundreds of mGal, while the lake corrections reach more than 5 mGal locally. Atmospheric effect taking into account topography was also calculated and compared with standard atmospheric correction.</p><p> </p>

scholarly journals GRAVIMETRIC GEOID MODELLING OVER PENINSULAR MALAYSIA USING TWO DIFFERENT GRIDDING APPROACHES FOR COMBINING FREE AIR ANOMALY

2019 ◽  
Vol XLII-4/W16 ◽  
pp. 515-522
Author(s):  
M. F. Pa’suya ◽  
A. H. M. Din ◽  
J. C. McCubbine ◽  
A. H. Omar ◽  
Z. M. Amin ◽  
...  
Keyword(s):  
Gravity Data ◽  
Reference Signal ◽  
Digital Terrain Model ◽  
Peninsular Malaysia ◽  
Airborne Gravity ◽  
Geopotential Model ◽  
Gravimetric Geoid ◽  
Geoid Model ◽  
Free Air ◽  
Free Air Anomaly

Abstract. We investigate the use of the KTH Method to compute gravimetric geoid models of Malaysian Peninsular and the effect of two differing strategies to combine and interpolate terrestrial, marine DTU17 free air gravity anomaly data at regular grid nodes. Gravimetric geoid models were produced for both free air anomaly grids using the GOCE-only geopotential model GGM GO_CONS_GCF_2_SPW_R4 as the long wavelength reference signal and high-resolution TanDEM-X global digital terrain model. The geoid models were analyzed to assess how the different gridding strategies impact the gravimetric geoid over Malaysian Peninsular by comparing themto 172 GNSS-levelling derived geoid undulations. The RMSE of the two sets of gravimetric geoid model / GNSS-levelling residuals differed by approx. 26.2 mm. When a 4-parameter fit is used, the difference between the RMSE of the residuals reduced to 8 mm. The geoid models shown here do not include the latest airborne gravity data used in the computation of the official gravimetric geoid for the Malaysian Peninsular, for this reason they are not as precise.

INTERPRETASI BAWAH PERMUKAAN GUNUNG ANAK RANAKAH DENGAN PEMODELAN DUA DIMENSI (2D) BERDASARKAN DATA ANOMALI GRAVITASI LOKAL

2018 ◽  
Vol 3 (1) ◽  
pp. 54-58
Author(s):  
Godensius Tematur ◽  
Jehunias L. Tanesib ◽  
Redi K. Pingak
Keyword(s):  
Continuation Method ◽  
Atmospheric Correction ◽  
Bouguer Anomaly ◽  
Geophysical Research ◽  
Subsurface Geology ◽  
Dimensional Modeling ◽  
Free Air ◽  
Geological Conditions ◽  
Free Air Anomaly ◽  
Surrounding Areas

ABSTRAK Penelitian geofisika dengan menggunakan metode gravitasi telah dilakukan di Gunung Anak Ranakah dan sekitarnya di kabupaten Manggarai Nusa Tenggara Timur pada bulan Juni sampai dengan bulan Juli 2016. Penelitian ini bertujuan untuk mengetahui kondisi geologi bawah permukaan daerah penelitian dengan menggunakan data anomali udara bebas dari Sandwell dan Smith 2016. Data tersebut direduksi dengan koreksi atmosfer, koreksi Bouguer Sederhana, dan koreksi kurvatur hingga memperoleh anomali Bouguer Lengkap. Data anomali Bouguer dibawa ke bawah bidang topografi dengan metode kontinuasi ke bawah sedalam 300 m menggunakan program Magpic. Selanjutnya dilakukan pemodelan 2 dimensi menggunakan program Grav2DC. Hasil yang diperoleh menunjukkan bahwa kondisi geologi bawah permukaan gunung Anak Ranakah dan Sekitarnya didominasi oleh batuan basalt (densitas 2,70 -3.30 ), andesit (densitas 2.4 -2.8 ), dan soil (densitas 1.2 -2.40 ). Kata kunci: Anomali Gravitasi, Pemodelan 2D, Gunung Anak Ranakah ABSTRACT Geophysical research by using the gravity method has been carried out on the Ranakah child mountain and surrounding areas in Manggarai Regency of East Nusa Tenggara in June until July 2016. This research aims to know the condition of the subsurface geology of the area of research using the free air anomaly data from Sandwell and Smith 2016. The data are reduced by atmospheric correction, Simple Bouguer correction, and the correction of curvature to obtain complete Bouguer anomalies. Bouguer anomaly data brought down the field topography with continuation method down as deep as 300 m using the Magpic. Then, 2 dimensional modeling is done using the Grav2DC. The results obtained show that the geological conditions under the surface of the Ranakah Child mountaoin and its surrounding area was dominated by basalt rocks (density of ), andesite (density of ), and soil rocks (density of ). Keywords: Gravity Anomaly, 2D Modelling, Ranakah child Mountain.

The Mid-Atlantic Ridge Near 45 °N. XX. The Gravity Field

1972 ◽  
Vol 9 (8) ◽  
pp. 942-959 ◽  
Author(s):  
J. M. Woodside
Keyword(s):  
Gravity Data ◽  
Bouguer Anomaly ◽  
Gravity Anomalies ◽  
Spreading Rate ◽  
Survey Area ◽  
Free Air ◽  
Mid Atlantic Ridge ◽  
Sea Floor Spreading ◽  
Relationship Of ◽  
East West

Detailed maps of free-air, Bouguer, and residual gravity anomalies for a survey area 250 km wide across the Mid-Atlantic Ridge between 45° and 46 °N have been compiled. The Bouguer anomaly was terrain-corrected to a radius of 40 km. The residual anomaly was computed from the terrain-corrected Bouguer anomaly using an empirical linear relationship between the Bouguer anomaly and the bathymetry to predict a 'regional' Bouguer anomaly from the depth data. North–south and east–west trends in the gravity data are enhanced in the residual anomaly; and it is suggested that at least one short east–west transform fault may offset the ridge in a right-lateral sense. The offset is presumably a response to a change in sea-floor spreading direction from west–northwest/east–southeast to west/east about 10 m.y. ago. A change in spreading rate may have occurred at the same time. A difference in accretion rate on either side of the ridge axis is indicated by asymmetry in the gravity data and by differences in the topographic compensation across the axis. Variations in the relationship of terrain-corrected Bouguer anomaly to bathymetry within the survey area suggest that a density deficiency or buoyant forces in the upper mantle are responsible for the overall elevation of the crestal mountain region but that the topography of the high-fractured plateau may be partially compensated by undulations of the crust–mantle interface.

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