Topography and geoid effects on gravity anomalies in mountainous areas as inferred from the gravity field of the Central Andes

Abstract

This paper is a critical test of reduction and processing techniques of gravity data in areas of rugged topography in which topographic relief and geoidal undulations attain often significant variations. First, we describe the definition of Free-air or Bouguer gravity anomalies as station anomalies and analyse the accuracy of routine reductions. Because heights are generally referred to mean sea level (approximately the geoid) not to the ellipsoidal surface, we then introduce corrections to the indirect effects of “free-air” and Bouguer reductions. The indirect effect caused by the “free-air” reduction and the simple Bouguer slab correction amount to some 10 mGal in the Central Andes. Only the indirect effect of curvature correction can be widely ignored. Most of the numerical processing techniques demand data on a horizontal plane. However, gravity fields processed by reduction routines can not satisfy this requirement. Therefore, a reduction-to-datum procedure becomes necessary.