Geoid and density anomalies

Abstract

Geoid undulations reflect density contrasts within Earth. In this study we show that many features known from other geophysical sources, such as gravity and magnetic anomaly maps, tectonic and geological maps, are also discernible in an accurate geoid. This suggests an association between these features and density anomalies. To demonstrate the usefulness of the geoid for geophysical interpretation we have chosen to use the “terrestrial contribution” to the UNB Dec. '86 Canadian geoid. This is a high‐resolution shorter wavelength (of degree and order higher than 20, or half wavelength less than 1000 km) part, which is readily available as a natural product of the geoid compilation when the UNB formulation of the geodetic boundary value problem is used. To facilitate the recognition of different features we have employed different image enhancement techniques. Hill shading combined with hypsometry (color coding of heights) appears to be the most promising in our context.

GEOID90: A high‐resolution geoid for the United States

“…In the state of Washington one sees the Columbia River plateau, and just to the southeast, the crescent shape of the Snake River plain is expressed in the geoid. It has been noted by Christou et al [1989], in their analysis of the UNB86 (University of New Brunswick) geoid model for Canada, that a high-resolution geoid will display structures that reflect den sity anomalies within the Earth. Foremost among these features is the Mid-Continent Gravity High, which runs south from Lake Superior.…”

Shaded relief map of U.S. topography from digital elevations

“…Shaded relief portrayal, more formally termed analytical hill shading, represents to pographic form by variations in mathemati cally determined light intensity [Horn, 1981;Christou et al, 1989]. Although a well-known manual technique, hill shading was impracti cal for large areas until Yoeli [1967] adapted it to computers and digital elevation data.…”

“…Batson et al [1975] made the first synoptic shaded relief images for parts of the U.S. (their images of several western states are soon to be distributed by the U.S. Geological Survey), Arvidson et al [1982] published the first shaded relief image of the continental U.S. (1:30,000,000 scale), and Loughridge [1986] presented the first shaded relief map of the Earth. Later experiments have further refined the technique, which also has been effective in portraying gravity, aeromagnetic, geoid, and other geophysical data for inter pretation [e.g., Arvidson et al, 1982;Verhoef et al, 1989;Christou et al, 1989; and references therein].…”

Geophysical signature of geological units inferred from the analysis of geoid maps in Cameroon and its surroundings

“…Therefore, geophysicists should find complementary geopotential field information whose form can be subject to a qualitative and a quantitative interpretation in terms of the internal properties of the subsurface. Many attempts to show the use of geoid in geophysics have already been carried out in the past years (Runcorn, 1967;Allan, 1972;Khan, 1977;Bowin, 1983;Silver et al, 1988;Christou et al, 1989;Vanicěk and Christou, 1994). However, these attempts were mainly limited to the analyses of gravity anomalies and geoid maps obtained from lower resolution global geopotential models (GGM).…”