The relationship between bathymetry and gravity in the Atlantic Ocean

Abstract

The free air gravity anomaly and depth are sampled at 2‐km intervals along two long, reasonably straight ship tracks across the Atlantic Ocean. The resulting series are then processed as if they were time series, and filters are obtained to predict the gravity observations from the bathymetry. More than half the energy in the gravity field can be predicted by this means, and that which cannot emphasizes unusual structures beneath the sea floor. More information can be obtained by comparing the gravity and the bathymetry after both series have been Fourier‐transformed. Isostatic compensation begins when the wavelength exceeds about 100 km and increases with increasing wavelength. The results are compared with predictions from various simple models and agree best with a model in which the topography results from variations of crustal thickness and the plate thickness is little greater than 10 km when the compensation occurs. These observations can be understood if the topography results from large‐scale intrusions into the lower crust within tens of kilometers of the spreading center. Though such a model for a slowly spreading ridge differs from most of those which have been previously put forward and must be regarded with skepticism until it is supported by evidence from other sources, it appears to be compatible with the limited information now available.

Effects of a low‐viscosity lower crust on topography and gravity at convergent mountain belts during gravitational instability of mantle lithosphere

“…[e.g., McKenzie and Bowin, 1976]. Making gravity dimensionless and scaling relative to the deflection of the LAB then yields a dimensionless admittance:…”

Lithosphere structure and upper mantle characteristics below the Bay of Bengal

“…For this purpose, the relationship between geoid/ gravity and the topography in the spectral domain (admittance / coherence) is utilized for better understanding the isostatic response of the topographic loads, and for studies related to thermo-mechanical characterization of the oceanic lithosphere and/or sub-lithospheric upper mantle. Several researchers have effectively used this approach i) for evaluating isostatic response of the oceanic lithospheric using free-air gravity/ geoid and bathymetry admittance function (e.g., McKenzie and Bowin, 1976;Watts, 1978;Black and McAdoo, 1988); ii) for estimation of flexural rigidity of continental lithosphere through Bouguer gravity and topography coherence function (Forsyth, 1985;Lowry and Smith, 1994;McKenzie and Fairhead, 1997;Simons et al, 2000;Swain and Kirby, 2003). In the present study, we analyzed the admittance between bathymetry and residual geoid on two wavelength scales, one using degree-10 residual geoid for modeling upper mantle convection processes, and other using degree-50 residual geoid for understanding mode of isostatic compensation along the 85°E and Ninetyeast ridges.…”

“…For each block, 256 E-W and N-S profiles of bathymetry and the residual geoid (degree-10) data were extracted from the grid, and these profiles were stacked to obtain average E-W and N-S bathymetry and geoid profile data sets. For these averaged profiles, admittance was computed using power spectrum of the bathymetry and cross spectra of the bathymetry and geoid data using the formula (after McKenzie and Bowin, 1976) ( ) ( ) ( ) ………….. (1) Where, k is the wave number, Z(k) admittance between geoid and bathymetry; C(k) is cross spectrum of the geoid and bathymetry, E b (k) is power spectrum of the bathymetry.…”

Applications of Geodesy to Geodynamics an International Symposium

“…Since the thickness of a plate influences its mechanical properties, it is possible to study the time evolution of the lithosphere by observing how it deforms when loaded by seamounts placed at several points along its evolutionary path. To examine the mechanical properties of the lithosphere, we assumed the thin-plate model developed by McKenzie and Bowin [1976]. In this model, the lithosphere consists of a thin elastic plate overlying a fluid medium; the plate is being loaded by bathymetric features such as seamounts, island chains, and ridges and is subsequently deformed.…”

“…This can be done in one of two ways: the first is to Fourier-transform the geoid height and the bathymetry into wavenumber space, divide the geoid height by the bathymetry, and obtain the response function as a function of wavelength; the flexural rigidity can then be deduced from the characteristics of this function. The second method is to calculate a theoretical filter Z(k) in wavenumber space by using the thin-plate model [McKenzie and Bowin, 1976] …”