Moho depth and sediment thickness estimation beneath the Red Sea derived from satellite and terrestrial gravity data

Abstract

We sought to map the depth and density contrast of the Mohorovičić discontinuity (Moho) across the Red Sea area and to model sedimentary thickness from gravity data. The gravity data that are used are a combination of satellite and terrestrial gravity data processed into a Bouguer anomaly grid. A 200-km low-pass filter was used to separate this grid into regional and residual gravity grids. We inverted the regional gravity grid to a Moho depth map based on a density contrast map that is constrained by published seismic results. The interpreted Moho is shallowest ([Formula: see text]) along the axis of the central Red Sea, [Formula: see text] along the axis to the south, and [Formula: see text] in the northern Red Sea. The depth increased to [Formula: see text] at the coast and 35–40 km in the adjacent continents. The residual gravity data provided insights into the tectonic fabric along the whole rift and provided a good correlation with magnetic lineaments where these are available. We used the complete Bouguer anomaly to model sedimentary thicknesses constrained by wells and the interpreted Moho. The modeling results are consistent with the presence of large-scale, ridge parallel tilted fault blocks forming subbasins with a maximum depth of about 6–7 km. Our models suggest that the northern Red Sea has an asymmetric basement surface with the western side deeper than the eastern side. The results indicate the presence of oceanic crust in the central and southern parts of the Red Sea, but not in the north. The very thin crust and interpreted oceanic crustal density in the central Red Sea suggest that this area is fully oceanic—although possibly quite young.

Estimation of depth to top of magnetic sources using the local-wavenumber approach in an area of shallow Moho and Curie depth — The Red Sea

“…(a) The local wavenumber of the magnetic data of Figure 6a after upward continuing the data by a distance of 1 km (elevation of 2 km in total). (b) The depth-to-basement results assuming infinite-contact (cross symbol) and finite-contact (circle symbol) models and the depth to the bottom of the magnetic layer defined by the depth to Moho, from Salem et al (2013).…”

“…The top of the magnetic layer was obtained from our finite local-wavenumber solutions. The bottom of the magnetic layer was assumed to be equivalent to the Moho (Salem et al, 2013) or the Curie isotherm as discussed above. Additional contacts were added between the local-wavenumber peaks to allow better fitting of the magnetic data.…”

Estimation of depth to top of magnetic sources using the local wavenumber approach in an area of shallow Moho and Curie depth – the Red Sea

“…We defined z b based on Moho depths determined from the 3D inversion of gravity anomaly data constrained by seismic results (Salem et al, 2013). Because the depth of the magnetic sources is controlled by the Curie temperature of magnetic minerals, we also computed the depth of the 580°C isotherm (the Curie temperature of magnetite).…”

“…This then removes the need to apply an extra stage of depth corrections to the depth estimate based on the infinite depth model. This approach has already been used to demonstrate a finite depth extent version of the tilt-depth method (Salem et al, 2013), whereas the present contribution presents a modification to the local-wavenumber method to deal with layers with a finite depth extent.…”

Inversion of gravity data with isostatic constraints

“…Jorgensen and Bosworth (1989) separate the gravity field using a best-fit, low-order polynomial to address a similar interpretation. Salem et al (2013) separate gravity data across the Red Sea into sediment and Moho effects based upon wavelength filtering. In each of these cases, the residual gravity can be inverted for basement depth using a method that inverts for the depth of a single interface, e.g., Cordell and Henderson (1968) in the space domain or Oldenburg (1974) using fast Fourier transforms.…”