FREE‐AIR GRAVITY ANOMALY MAP OF THE GULF OF MEXICO AND ITS TECTONIC IMPLICATIONS, 1963 EDITION

Geophysics ◽  
1965 ◽  
Vol 30 (1) ◽  
pp. 102-110 ◽  
Author(s):  
Peter Dehlinger ◽  
B. R. Jones
Keyword(s):  
Gulf Of Mexico ◽  
Cross Sections ◽  
Seismic Refraction ◽  
Seismic Velocities ◽  
Surface Ship ◽  
Free Air ◽  
Anomaly Map ◽  
Free Air Gravity ◽  
Free Air Anomaly ◽  
Mohorovičić Discontinuity

As part of a continuing program, Texas A. and M. University has been making a surface‐ship gravity survey of the Gulf of Mexico. The 1963 free‐air anomaly map of the Gulf is the second in a series of maps resulting from these investigations; it includes not only a larger area than the first map, but also measurements having considerably higher accuracies. The present map indicates, as the first one suggested, that the Gulf of Mexico is essentially in isostatic equilibrium but contains local mass anomalies. Two cross sections of crustal layers were constructed which are consistent with the gravity observations and published seismic‐refraction results. One section extends from Galveston, Texas, to the Yucatan Peninsula, and the other from the Sigsbee Deep to Florida. Both sections consist of four to six layers, in which layer densities were assumed to be uniform laterally and the density below the Mohorovičić discontinuity constant. Densities of the layers were converted from seismic velocities using the Drake and Nafe curves. A free‐air anomaly profile across the Cayman Trench is included.

Isostatic response to loading of the crust in Canada

1970 ◽  
Vol 7 (2) ◽  
pp. 716-727 ◽  
Author(s):  
R. I. Walcott
Keyword(s):  
Close Association ◽  
Ice Sheet ◽  
Ground Surface ◽  
Gravity Anomalies ◽  
A Value ◽  
Free Air ◽  
Ice Loads ◽  
Anomaly Map ◽  
Free Air Gravity ◽  
Free Air Anomaly

A smoothed free air anomaly map of Canada indicates that the central part of the region occupied by the Laurentide Ice Sheet is over-compensated. Due to the close association of the free air gravity, the apparent crustal warping, the time of deglaciation, and the congruence of the gravity anomalies and the Wisconsin Glaciation, it is concluded that the over-compensation is due to incomplete recovery of the lithosphere from the displacement caused by the Pleistocene ice loads. The amplitude of the anomalies, about –50 milligals, suggests that a substantial amount of uplift has yet to occur and that the relaxation time of crustal warping is of the order of 10 000 to 20 000 y.The profile of the ground surface at the edge of a continental ice sheet on an elastic lithosphere is assessed using a value of the flexural parameter of the lithosphere calculated from gravity and deformation studies in the Interior Plains. The conclusions are: (a) a purely elastic forebulge is not likely to reach an amplitude of more than a few tens of meters; (b) the crust will be depressed for a considerable distance beyond the edge of the ice sheet; and (c) for large ice sheets crustal failure will probably occur in a preferential zone several hundred kilometers inside the maximum ice limit.

Free Air Anomaly Map of Canada from Piece-Wise Surface Fittings Over Half-Degree Blocks

1973 ◽  
Vol 27 (4) ◽  
pp. 293-300 ◽  
Author(s):  
Dezsö Nagy
Keyword(s):  
Gravity Anomaly ◽  
Extreme Values ◽  
Free Air ◽  
Equivalent Length ◽  
Order Polynomial ◽  
Standard Deviations ◽  
Anomaly Map ◽  
Half Degree ◽  
Free Air Anomaly ◽  
Polynomial Surface

The region of Canada, which has been covered by gravity surveys (including 1970 data), has been subdivided into 2,923 surface elements of sides of a half-degree along the meridian and approximately equivalent length along the parallels. The gravity anomaly at the center of each element was estimated by fitting a low-order polynomial surface to the free air anomalies within each element. The extreme values are —160 and 96 milligals, with over 85 per cent of the anomalies being in the range of —40 and 20 milligals. About two thirds of all computed anomalies are estimated to have standard deviations less than ±10 milligals.

scholarly journals The Regime of the Western Part of the Ross Ice Shelf Drainage System

1966 ◽  
Vol 6 (43) ◽  
pp. 55-68 ◽  
Author(s):  
M. Giovinetto ◽  
Edwin S. Robinson ◽  
C. W. M. Swithinbank
Keyword(s):  
Cross Sections ◽  
Drainage System ◽  
Gravity Anomalies ◽  
Ice Shelf ◽  
Glacier Surface ◽  
Ross Ice Shelf ◽  
Movement Data ◽  
Free Air ◽  
The Difference ◽  
Free Air Gravity

AbstractThe net mass budget is estimated for the western part of the Ross Ice Shelf drainage system. The area of the system is (1.75±0.26) × 106 km.2, and the drainage periphery extends along the eastern flank of the Trans-Antarctic Mountains between lat. 77° 58′ S., long. 164° 37′ E. and lat. 85° 27′ S., long. 147°50′ discharge is estimated from vertical cross-sections and corresponding ice-movement data for eight outlet glaciers. Free-air gravity anomalies, corrected for the effect of terrain above the glacier surface, are used to determine cross-sections of valleys by comparison with theoretical gravity profiles for several two-dimensional valley models. These data provide a basis for estimating the rate of ice discharge from the plateau, which is compared with the estimated rate of net accumulation at the surface, to determine the net budget of the ice sheet in the region. Representative mean rates of ice discharge measured in different types of glaciers are approximately 0.25 × 1015 g. km.−1 yr.−1 in outlet glaciers with large basins, and 0.05 × 1015 g. km.−1 yr.−1 in outlet glaciers with small basins. Taking into account the snowshcd area and the rate of accumulation, the rate of ice discharge in cirque and piedmont glaciers is estimated at about 0.02 × 1015 g. km.−1 yr.−1 The difference ((48±29) × 1015 g. yr.−1) between mass input ((96±25) × 1015 g. yr.−1) and mass output ((48±15) × 1015 g. yr.−1) is large enough relative to the estimated standard error to indicate a probable positive net budget.

Sign in / Sign up

Export Citation Format

Share Document