Modes of Gravity Anomaly Distributions in Relation to the Crustal Structure of the Antarctic Continent

Abstract

An analytical method is introduced in applying the gravity data to the study of crustal structure by using a reduced gravity anomaly when the thickness of ice sheet is unknown. The reduced gravity anomaly designated as Δg_h(mgal) is defined by the equation of Δg_h=Δg_0-2πGρ(H-h), where Δg_0(mgal) is the free air anomaly, H(m) is the elevation of measurement point and h(m) is the elevation of the point to which gravity anomaly Δg_h should be reduced. The density of ice sheet and the universal constant of gravitation are designated as ρ(g/cm^3) and G respectively. For the practical convenience, the value of h should be taken as constant and larger than or equal to the maximum value of H. The space bounded by the two levels of h and H is assumed to be filled up with ice sheet with density ρ in the reduction procedure. The reduced gravity anomaly Δg_h thus introduced is physically equivalent to the free air anomaly reduced to the points on the surface of ice sheet extending with the constant elevation h. Predominant modes of the spatial distribution of reduced gravity anomalies Δg_ are found in two ranges of wave length, i.e., the shorter wave-length range of 100-200 km and the longer wave-length range of more than l,000 km. The mode of the shorter wave-length range is possibly correlated with topographical features of the rock and ice sheet interface, while the mode of the longer wavelength range is characterized by a decrease of Δg_ toward the inland cart of the continent. The result of the gravity data analysis leads to a conclusion that the crust of the Antarctic Continent is in a regional isostatic equilibrium common to the other continental regions on the earth, though the thickness of the crust in West Antarctica is relatively thinner than that in East Antarctica.