Terrain corrections for borehole gravity measurements

Geophysics ◽  
1979 ◽  
Vol 44 (9) ◽  
pp. 1584-1587 ◽  
Author(s):  
Larry A. Beyer
Keyword(s):  
Density Profiles ◽  
Gravity Measurements ◽  
Vertical Density ◽  
Terrain Corrections ◽  
Made In

This note presents examples of terrain corrections calculated for borehole gravity surveys made in a variety of topographic settings. The effect of terrain corrections on vertical density profiles calculated from borehole gravity measurements also is shown.

scholarly journals Thickness and Basal Configuration of Lower Blue Glacier, Washington, Determined by Gravimetry

1965 ◽  
Vol 5 (41) ◽  
pp. 637-650 ◽  
Author(s):  
Charles E. Corbató
Keyword(s):  
Gravity Field ◽  
Three Dimensional ◽  
Successive Approximations ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Gravity Measurements ◽  
Computational Errors ◽  
Terrain Corrections ◽  
Seismic Reflections ◽  
Regional Gravity

AbstractGravity measurements at 146 stations on lower Blue Glacier were used to determine the subglacial bedrock configuration. The gravity values, station elevations and density contrast were carefully measured, and terrain corrections thoroughly evaluated to insure accuracy of the Bottguer anomalies. A series of successive approximations results in evaluation of the regional gravity field and a three-dimensional model of the glacier whose gravimetric effects fit the range of the observational and computational errors. Comparison with bore holes and seismic reflections indicates no significant errors in the model and accuracies of 5–10 per cent in the calculated thicknesses of the glacier.

scholarly journals Gravity Measurements on the Athabaska Glacier, Alberta, Canada

1963 ◽  
Vol 4 (35) ◽  
pp. 617-631
Author(s):  
E. R. Kanasewich
Keyword(s):  
Cross Section ◽  
Three Dimensional ◽  
Gravity Anomalies ◽  
Independent Data ◽  
Surface Slope ◽  
Average Shear Stress ◽  
Glacier Valley ◽  
Gravity Measurements ◽  
Average Shear ◽  
Made In

AbstractThe thickness of the Athabaska Glacier has been obtained along eight transverse profiles by an investigation of gravity anomalies. Three-dimensional computations with a low-speed digital computer were made in this study to acquire more precise results than previously obtained. The thickness of the glacier varies front 326 m. on a line below the lower ice fall to 49 m. near the terminus. The accuracy of the results is discussed and compared with independent data from bore holes and a seismic program. The cross-section of the glacier valley was found to approximate a parabola on several lines. From a knowledge of the thickness. shape and surface slope of the glacier, the average shear stress exerted by the bed on the ice was found to be 1.0 bar.

Ammonia vertical density profiles in Jupiter and Saturn from their radioelectric and infrared emissivities

Icarus ◽  
1980 ◽  
Vol 41 (3) ◽  
pp. 410-422 ◽  
Author(s):  
André Marten ◽  
Régis Courtin ◽  
Daniel Gautier ◽  
Anne Lacombe
Keyword(s):  
Density Profiles ◽  
Vertical Density

Density determinations of basic volcanic rocks of the Yellowknife supergroup by gravity measurements in mine shafts—Yellowknife, Northwest Territories

Geophysics ◽  
1980 ◽  
Vol 45 (1) ◽  
pp. 18-31 ◽  
Author(s):  
R. A. Gibb ◽  
M. D. Thomas
Keyword(s):  
Volcanic Rocks ◽  
Volcanic Belt ◽  
Mine Shaft ◽  
Average Interval ◽  
Basaltic Rocks ◽  
Surface Samples ◽  
Gravity Measurements ◽  
Vertical Density ◽  
Basic Volcanic

Gravity measurements were made in two gold mine shafts sunk in the Archean Yellowknife greenstone belt to determine the in‐situ densities of basic volcanic rocks of the Kam formation, Yellowknife supergroup. Thirteen stations were occupied between the surface and a depth of 608 m at an average interval of about 50 m in the C shaft of Giant Yellowknife Mines Limited, and 14 stations were occupied between the surface and a depth of 1598 m at an average interval of about 120 m in the Robertson shaft of Con mine, Cominco Limited. Densities were computed using the terminology of borehole gravimetry with appropriate corrections for surface terrain and underground voids such as shafts, drifts, and stopes. Weighted mean in‐situ densities of [Formula: see text] (36 to 608 m depth) and [Formula: see text] (surface to 1598 m depth) were obtained from the gravity measurements for the Giant and Robertson sections, respectively; these values compare with mean densities of 2.82 and [Formula: see text] obtained from rock samples collected at the underground gravity stations. Sheared specimens and massive specimens collected at both underground and surface gravity stations have mean densities of 2.80 and [Formula: see text], respectively. Unaltered surface samples collected at stratigraphic intervals of about 150 m throughout the entire volcanic sequence have a mean density of [Formula: see text]. Core samples obtained from holes drilled from the bottom of C shaft extend the vertical density profile for the Giant section from a depth of 608 to 1416 m; the mean density of these samples is [Formula: see text]. The lower bulk densities obtained from the mine shaft experiments reflect in part the high proportion of sheared rocks and in part the presence of lower‐density members of the Kam formation (andesite, dacite, tuff, breccia, and agglomerate) in the vicinity of the shafts, as opposed to purely massive basaltic rocks. A density of [Formula: see text] based on the proportion of low‐ and high‐density rocks in the volcanic belt is considered to be more representative of the Kam formation as a whole.

Abrupt transitions between gyroscopic and internal gravity waves: the mid-latitude case

2008 ◽  
Vol 598 ◽  
pp. 67-80 ◽  
Author(s):  
HANS VAN HAREN
Keyword(s):  
Large Scale ◽  
Deep Ocean ◽  
Internal Gravity Waves ◽  
Buoyancy Frequency ◽  
Neutral Stability ◽  
Density Profiles ◽  
Geostrophic Balance ◽  
Convective Mixing ◽  
Vertical Density ◽  
Wave Limit

The large-scale vertical density stratification, represented by buoyancy frequency N, is generally very stable in the upper half of the ocean, and relatively weak in the lower half. However, closer inspection of density profiles demonstrates steps rather than a smooth increase with depth. As is demonstrated here using Richardson number, geostrophic balance and slantwise convective mixing arguments, these layers have a limited set of minimum, weak stratification, N-values Nmin indicating the transition between stably stratified and convective ‘homogeneous’ layers. Adopting the viewpoint that the transition occurs for neutral stability in the direction of Earth's rotation Ω instead of gravity g, three discrete states are hypothesized for mid-latitudes: (i) Nmin = 2fh under linear stability conditions, (ii) Nmin = fh(|ϕ| < 45°) and (iii) Nmin = 4fh, both under nonlinear stability, where horizontal component fh = 2Ω cos ϕ at latitude ϕ. The Nmin are not in terms of inertial frequency f = 2Ω sin ϕ, because the effect of fh is the tilting of vortex tubes away from the local vertical in the direction of Ω. The above explains very well deep-ocean North-Atlantic and Mediterranean observations on transitions in conductivity-temperature with depth profiles, inertial polarization and near-inertial shear. The latter peaks at sub-inertial 0.97f, which is associated with the lower inertio-gravity wave limit for Nmin = 4fh, thereby stressing the importance of fh for the dominant physics associated with mixing in the ocean.

Developing an autonomous unmanned aerial system to estimate field terrain corrections for gravity measurements

2018 ◽  
Vol 37 (8) ◽  
pp. 584-591 ◽  
Author(s):  
Leon Kaub ◽  
Christopher Seruge ◽  
Shaurya D. Chopra ◽  
Jonathan M. G. Glen ◽  
Mircea Teodorescu
Keyword(s):  
Unmanned Aerial System ◽  
Gravity Measurements ◽  
Terrain Corrections

scholarly journals Gravity Measurements on the Athabaska Glacier, Alberta, Canada

1963 ◽  
Vol 4 (35) ◽  
pp. 617-631 ◽  
Author(s):  
E. R. Kanasewich
Keyword(s):  
Cross Section ◽  
Three Dimensional ◽  
Gravity Anomalies ◽  
Independent Data ◽  
Surface Slope ◽  
Average Shear Stress ◽  
Glacier Valley ◽  
Gravity Measurements ◽  
Average Shear ◽  
Made In

AbstractThe thickness of the Athabaska Glacier has been obtained along eight transverse profiles by an investigation of gravity anomalies. Three-dimensional computations with a low-speed digital computer were made in this study to acquire more precise results than previously obtained. The thickness of the glacier varies front 326 m. on a line below the lower ice fall to 49 m. near the terminus. The accuracy of the results is discussed and compared with independent data from bore holes and a seismic program. The cross-section of the glacier valley was found to approximate a parabola on several lines. From a knowledge of the thickness. shape and surface slope of the glacier, the average shear stress exerted by the bed on the ice was found to be 1.0 bar.

Gravity measurements in the English Channel

1952 ◽  
Vol 139 (896) ◽  
pp. 426-447 ◽  
Keyword(s):  
English Channel ◽  
British Isles ◽  
The West ◽  
Northern France ◽  
Gravity Measurements ◽  
Made In

In 1948 gravity measurements were made in a submarine at forty-three stations in the English Channel and at Portland, Devonport, Gosport and Cherbourg. There are also five stations in the area at which measurements were made in 1946. The anomalies are shown to be compatible with an interpretation of existing knowledge of the Mesozoic geology of the Channel basin provided that reasonable assumptions are made. An area of strong negative anomalies off the French coast in the Cherbourg-Le Havre area extends about half-way across the Channel. These must be explained by intracrustal masses. The anomalies show the same trend to positive values in the west as is found in the British Isles and northern France.

Inclined gravity currents filling basins: the impact of peeling detrainment on transport and vertical structure

2017 ◽  
Vol 820 ◽  
pp. 400-423 ◽  
Author(s):  
Charlie A. R. Hogg ◽  
Stuart B. Dalziel ◽  
Herbert E. Huppert ◽  
Jörg Imberger
Keyword(s):  
Gravity Current ◽  
Uniform Density ◽  
Ambient Fluid ◽  
Transport Pathway ◽  
Density Profiles ◽  
Model Match ◽  
Dense Fluid ◽  
Vertical Density ◽  
Multiprocess Models ◽  
The Impact

Transport of dense fluid by an inclined gravity current can control the vertical density structure of the receiving basin in many natural and industrial settings. A case familiar to many is a lake fed by river water that is dense relative to the lake water. In laboratory experiments, we pulsed dye into the basin inflow to visualise the transport pathway of the inflow fluid through the basin. We also measured the evolving density profile as the basin filled. The experiments confirmed previous observations that when the turbulent gravity current travelled through ambient fluid of uniform density, only entrainment into the dense current occurred. When the gravity current travelled through the stratified part of the ambient fluid, however, the outer layers of the gravity current outflowed from the current by a peeling detrainment mechanism and moved directly into the ambient fluid over a large range of depths. The prevailing model of a filling box flow assumes that a persistently entraining gravity current entrains fluid from the basin as the current descends to the deepest point in the basin. This model, however, is inconsistent with the transport pathway observed in visualisations and poorly matches the stratifications measured in basin experiments. The main contribution of the present work is to extend the prevailing filling box model by incorporating the observed peeling detrainment. The analytical expressions given by the peeling detrainment model match the experimental observations of the density profiles more closely than the persistently entraining model. Incorporating peeling detrainment into multiprocess models of geophysical systems, such as lakes, will lead to models that better describe inflow behaviour.

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