The Effect of Seamounts and Other Bottom Topography on Marine Gravity Anomalies,
Abstract
Localized bathymetric features produce large amplitude perturbations in the marine free-air gravity anomalies. In order to study long wavelength anomalies, which are of particular interest in marine geodesy, it is desirable to remove the topography 'noise level'. However, to do this in a truly three-dimensional fashion along a marine gravity track is not practical becuase of the formidable amount of data preparation required. It is also undesirable to use conventional Bouguer anomalies becuase these can easily be in error by 60% because of the one-dimensional nature of the correction. A computer progam was developed which calculates the sea-surface three-dimensional gravity effect of a conical seamount from a point above the apex to any distance off-axis. The results of this program are compared with those of a Talwani two-dimensional equivalent of a ship track across the off-axis hyperbolic slice of the cone. A study of more than 100 seamounts in the Pacific Ocean showed that their slope angles of from 4.5 to 17 degrees. For this reason, model cases with slope angles of 5, 10 15 degrees in water depths of 1 to 6 km were considered. For a seamount with its apex at 2-km depth and base at 5-km depth and 10 degree slope angle, the two-dimensional method over-corrects by 18 percent over the apex, but gives the same result as the three-dimensional method at an off-axis distance of 60 percent of the base radius. Farther out than 60 percent of the base radius, the two-dimensional method undercorrects. We have developed a second computer program which uses a two-dimensional method to correct the free-air anomaly for topography along the ship's track.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1974
- Accession Number
- ADA033202
Entities
People
- Bruce R. Bowman
- Johm C. Rose