Bathymetry sediment thickness and crustal structure from satellite gravity data

Abstract

Analysis of satellite gravity data offers an opportunity to rapidly evaluate the sedimentary structure of frontier basins. The accurate and evenly distributed measurements of the gravity field determined from satellite orbits contain information about the bathymetry, sediment thickness and crustal structure of the world's oceans. These data have been used by various authors, e.g., Smith and Sandwell (1994), to predict bathymetry for ocean basins where sediment cover is thin and where crustal structure is well known. In these areas, over a short wavelength band (15-160 km), the gravity field is highly correlated with the bathymetry. Along continental margins, however, the gravity field is complicated by sedimentary basins and changes in crustal structure. The method presented here differs from previous techniques for analysis of satellite gravity data by inverting simultaneously for water, sediment and crustal thickness instead of decomposing spectral bands in the gravity field. The inversion is constrained by interpretations of seismic and other data, and by assumptions about the nature and spatial variability of the interfaces. The seabed, basement and crust/mantle boundaries are defined by a series of triangular facets, whose size varies as the amount of constraining data changes. The sediment/basement boundary and the base of the crust are defined by larger facets than those defining the bathymetry. Conditioning equations smooth the interfaces, make the depths tend towards the input values and ensure that the interfaces do not intersect. In areas of sparse bathymetric and crustal structural control a degree of ambiguity between long-wavelength shallow structures and short-wavelength deeper features inevitably remains. This technique has been used to identify the presence and location of several sedimentary basins in an area 1250 by 1000 km west of New Zealand.