Hudson Bay, Bouguer anomaly map and free air anomaly map, scale 1:1,000,000

10.4095/8311 ◽  
1977 ◽  
Author(s):  
Keyword(s):  
Bouguer Anomaly ◽  
Hudson Bay ◽  
Free Air ◽  
Anomaly Map ◽  
Bouguer Anomaly Map ◽  
Map Scale ◽  
Free Air Anomaly

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>

STRUCTURAL IMPLICATIONS OF THE GRAVITY FIELD IN HUDSON BAY AND VICINITY

1967 ◽  
Vol 4 (5) ◽  
pp. 977-993 ◽  
Author(s):  
M. J. S. Innes ◽  
A. K. Goodacre ◽  
J. R. Weber ◽  
R. K. McConnell
Keyword(s):  
Gravity Field ◽  
Volcanic Rocks ◽  
Bouguer Anomaly ◽  
Major Change ◽  
Hudson Bay ◽  
Important Conclusion ◽  
Basement Rocks ◽  
Anomaly Map ◽  
Bouguer Anomaly Map ◽  
Basic Volcanic

The results of underwater gravity measurements of a reconnaissance nature in Hudson Bay and of regional gravity surveys over adjoining regions of the Canadian Shield and Hudson Bay Lowlands are presented in the form of a Bouguer anomaly map. The general anomaly pattern is discussed and an interpretation is presented. Analysis of anomaly profiles crossing Hudson Bay using seismic data for control, shows (1) that Paleozoic and recent sediments have little overall effect on the gravity field, and (2) that variations in depth to the crust-mantle boundary have little or no correspondence with variations in the gravity field. It is believed that the gravity variations are largely due to systematic density differences in the Precambrian basement rocks. An important conclusion is that the more positive gravity field over the northern part of Hudson Bay marks a major change in structure and that the Churchill crustal block does not extend uninterruptedly eastward; it is suggested that the positive anomalies reflect high-density metamorphic gneiss or basic volcanic rocks underlying the sedimentary veneer. Evidence is presented which strengthens the hypothesis that the Kapuskasing gravity anomaly and its northern and southern extensions mark an ancient zone of crustal rifting of continental proportion.

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