HR: 0800h
AN: G51C-0098    [Abstracts]
TI: Gravity Inversion Predicts Sediment Thickness in the Norwegian-Greenland Sea
AU: * Engen, O
EM: oyvind.engen@geo.uio.no
AF: Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, Oslo, 0316 Norway
AU: Wessel, P
EM: pwessel@hawaii.edu
AF: Department of Geology and Geophysics, School of Ocean and Earth Science and Technology (SOEST), University of Hawai'i at Manoa, 1680 East-West Road, Honolulu, HI 96822 United States
AU: Faleide, J I
EM: j.i.faleide@geo.uio.no
AF: Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, Oslo, 0316 Norway
AU: Frazer, N
EM: neil@soest.hawaii.edu
AF: Department of Geology and Geophysics, School of Ocean and Earth Science and Technology (SOEST), University of Hawai'i at Manoa, 1680 East-West Road, Honolulu, HI 96822 United States
AB: The Norwegian-Greenland Sea has formed by the Eurasia and Greenland plates separating across the Mohn and Knipovich ridges since the earliest Eocene. Whereas the Lofoten Basin on the Norwegian side is relatively well mapped by multi-channel (MCS) and wide-angle seismic data, few details are known about sediments in the Greenland and Boreas basins offshore Greenland. However, the gravity field of the entire sea is freely available from satellite altimetry, as is the bathymetry from the International Bathymetric Chart of the Arctic Ocean. We therefore explore the feasibility of using these gridded datasets along with prior geological knowledge in a 3-D prediction of sediment thickness beyond seismic calibration points. Although this problem is similar to other workers$\'{}$ predictions of bathymetry or crustal thickness, we find it difficult to separate the gravity signal of deep-ocean sediments from that of the underlying basement. Moreover, the thermal mantle structure beneath midocean ridges and continental margins is only in part compensated by the crustal topography, thus gravity modeling of only shallow surfaces may be misleading. We mitigate these problems by first assuming that the oceanic crust has constant density and thickness. Second, we approximate the thermal gravity field by the field calculated for a stack of 2-D finite-difference models of the seafloor spreading and cooling. The inversion is carried out by an iterative scheme where 1) the bottom of the sediment layer is calculated by damped downward continuation of the residual gravity; and 2) an updated residual is forward calculated from the Parker formula. The model space is further constrained by depths and density estimates from boreholes and an extensive velocity database. The maximum-likelihood solution predicts sediment basins on spatial scales greater than 20-25 km. It broadly agrees with existing MCS profiles in areas where the oceanic crust follows our assumptions, but is less accurate near seamounts and submarine ridges. We expect that our method can be used as a rapid 3-D exploration tool in frontier areas where seismic data are sparse due to logistic challenges or previous lack of commercial interest, notably in the Arctic Ocean.
DE: 9315 Arctic region
DE: 3010 Gravity
DE: 3260 Inverse theory
DE: 1219 Local gravity anomalies and crustal structure
DE: 0903 Computational methods, potential fields
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting