An Evaluation of the Gravity Control Network in North America

Behrendt, John C.; Woollard, George P.

doi:10.1190/1.1438845

Cited by 34 publications

(23 citation statements)

References 2 publications

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“…Vertical control was based on U. S. Coast and Geodetic Survey and U. S. Geological Survey bench marks, surveyed road intersections, or the average reading of two altimeters. The absolute values for gravity at the new stations were obtained by making ties with control stations in the airport network [Woollard, 1958;Behrendt and Woollard, 1961] at Minneapolis, Mankato, and Rochester, Min nesota, and at LaCrosse, Wisconsin.…”

Section: Gravity Observations and Reduc'rionmentioning

confidence: 99%

A gravity investigation of the Precambrian of southeastern Minnesota and western Wisconsin

Craddock¹,

Thiel²,

Gross³

1963

J. Geophys. Res.

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A southward-trending axis of Bouguer anomaly maximums as high as +53 mgal flanked by subparallel axes of anomaly minimums as low as -75 and -89 mgal has been demonstrated in southeastern Minnesota by ten westward-trending traverses consisting of a total of 2572 gravity observations taken at half-mile intervals. The maximum coincides with a belt of Middle Keweenawan basic igneous rocks as thick as about 29,000 feet near Minne apolis and prob ably thicker southward; the minimums are considered to reflect adjacent belts of less dense Upper Keweenawan sedimentary rocks as thick as about 11,000 feet. Two narrow zones of high gravity gradients that parallel the anomaly maximum northeast of Minneapolis are interpreted as defining steep faults which bound a major crustal feature, the St. Croix horst; this block has been elevated thousands of feet, mainly in late Precambrian time. An abrupt bend in the anomaly maximum southwest of Minneapolis may result from sinistral strike-slip movement o.f about 30 miles along a fault of Precambrian age that strikes N35°W.Minor rejuvenation of these Precambrian tectonic elements can account for many structural features developed in the Paleozoic strata. Near the southern Minnesota border the anomaly curve can be interpreted as resulting from a root of basic igneous rocks about ten miles thick below Upper Keweenawan strata as much as two miles thick. The Middle Keweenawan igneous province extends southward at least to Le Sueur County, Minnesota, and probably into Iowa.

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Section: Gravity Observations and Reduc'rionmentioning

confidence: 99%

A gravity investigation of the Precambrian of southeastern Minnesota and western Wisconsin

Craddock¹,

Thiel²,

Gross³

1963

J. Geophys. Res.

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“…

Gravity connections to Vostok have been made through two routes, one from Mirny and the other from McMurdo. Another correction to be applied (Behrendt and others 1962) results from a change in the calibration factor for LR1, according to measurements made in 1959 along the North American standardization range (Behrendt and Woollard, 1961). It is therefore worth examining these ties in some detail.

Ties from Mirny

Sparkman in 1957-58 made the first gravity determination at Mirny (Tardi, 1964).

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confidence: 99%

Gravity determinations at Vostok

Bentley¹

1980

Polar Record

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Gravity connections to Vostok have been made through two routes, one from Mirny and the other from McMurdo. These ties are of general interest for gravimetric studies in Antarctica, because they provide a direct airborne link between the stations upon which two major gravitational networks (American and Soviet) are based. It is therefore worth examining these ties in some detail. Ties from MirnySparkman in 1957-58 made the first gravity determination at Mirny (Tardi, 1964). Using LaCoste and Romberg gravimeter No 1 (LR1), he tied the chapel at McMurdo and the station at Mirny. The gravity value for the McMurdo chapel, quoted in the Annals of the International Geophysical Year (Tardi, 1964), corresponds to the 982.9928 gal value then accepted for the pendulum site in Building 30 (McMurdo A), based on Washington, DC (980.1188 gal). However, the more recently adopted value for McMurdo A (Behrendt and others , 1962; Woollard and Rose, 1963), which has been used since 1961, is 982.9919 gal. Thus Sparkman's value for Mirny should be reduced by 0.9 mgal. Another correction to be applied (Behrendt and others 1962) results from a change in the calibration factor for LR1, according to measurements made in 1959 along the North American standardization range (Behrendt and Woollard, 1961). Although the numerical recalibration of the gravimeter is not given by Behrendt and Woollard (1961), a correction of -0.8 mgal can be determined by comparing the uncorrected measurements by Sparkman using LR1 at McMurdo, Hallett, Byrd and South Pole stations (Thiel and others, 1959) with the corrected values (Behrendt and others, 1962). Both of these corrections should be applied to Sparkman's value for Mirny (Tardi, 1964), reducing it from 982.4074 gal to 982.4057 gal.The next determination was by pendulum (Woollard and Rose, 1963), yielding a value for Mirny of 982.4052 gal, also based on Washington. The most recent determination was by Elstner and Wirth (1967), and yielded a value for Mirny of 982.4067 gal. This value, however, is based on Potsdam rather than Washington.The difference between 'Astropoint No 1' at Vostok and Mirny, measured by Schneider (1973) with Askania gravimeter Gs-11 No 140, is -0.4985 ± 0.004 mgal 1 . Applied respectively to the determinations by Sparkman, Woollard and Rose, and Elstner and Wirth at Mirny, this gives values of 981.9072 gal, and 981.9067 gal based on Washington, and 981.9082 gal based on Potsdam, respectively.

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“…The original calibration and datum standards for the 1968 Alaskan gravity base network were provided by Behrendt (1961) and by Woollard and Rose (1963), who listed all observed gravities to the nearest 0.1 mgal. However, modern gravimeters are read to about 0.01 mgal so that roundoff errors using the Woollard-Rose standard could cause calibration uncertainties of at least one part in 10,000 whenever a meter was checked between gravity stations differing by less than 500 mgals.…”

Section: Gravimetry Scale and Meter Calibrationsmentioning

confidence: 99%

Southeast Alaska gravity base station network

Barnes¹

1972

Open-File Report

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An Evaluation of the Gravity Control Network in North America

Cited by 34 publications

References 2 publications

A gravity investigation of the Precambrian of southeastern Minnesota and western Wisconsin

A gravity investigation of the Precambrian of southeastern Minnesota and western Wisconsin

Gravity determinations at Vostok

Southeast Alaska gravity base station network

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