Directory Identifier: GRAVCD-id_iso
Directory Title: Idaho Batholith Study Area Isostatic Gravity Grid
Principal Investigator: Numerous

Contributing Organization: U.S. Geological Survey
EROS Data Center User Services
Sioux Falls, SD 57198

Summary: A 2 kilometer isostatic gravity grid for the Idaho batholith study area. Number of columns is 331 and number of rows is 285. The order of the data is from the lower left to the right and then up one row.

ISOSTATIC GRAVITY GRID

An isostatic residual gravity data set was calculated using the ISOCOMP program (Jachens and Roberts, 1981), which is based on the Airy-Heiskanen model of local compensation (Heiskanen and Vening Meinesz, 1958, p. 135-137). This map was created by removing from the Bouguer gravity field a model of the gravity expression caused by deficiencies in mass (compensating mass) that support topographic loads. The resulting isostatic residual anomalies do not imply either local isostatic compensation or imbalances. Instead, they reflect corrections that are the result of removing a predicted gravity response (the attraction of compensating mass) and are similar to other corrections made by removing predicted gravity responses from the observed gravity data, such as free-air and Bouguer adjustments. The use of isostatic corrections is further explained in Simpson and others (1986). For this study, the calculation of the isostatic residual gravity field used averaged digitized topography, a crustal thickness of 30 km, a crustal density of 2.67 g/cm^^3, and a density contrast between the crust and upper mantle of 0.35 g/cm^^3. These values were used by Simpson and others (1986) to calculate the isostatic residual gravity field of the conterminous United States. After the isostatic correction was applied at each gravity station, the data were gridded using a 2-km spacing.

CAVEAT: Caution is recommended when using these data. This data increment was provided to NGDC with minimal documentation. NGDC will continue to seek improved documentation as part of a routine and on-going data rescue effort.

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