GRAVIMETRIC ANALYSIS OF THE MID-EGYPTIAN GRABEN ARRAY (MEGA)

A number of abnormally narrow (2-5 km) yet extremely long (over 400 km) horst-and-graben structures are located west of Sohag and parallel to the Nile Valley in Egypt. These features are visible in the remote sensing imagery, namely radar satellite and Shuttle Radar Topography Mission - Digital Elevation Model (SRTM-DEM) data. We are referring to these features in aggregate as the Mid-Egyptian Graben Array (MEGA). Using gravity data from the World Gravity Map (WGM) 2012 gravity model, the 2D radially averaged spectrum curves of the related region were analyzed, since distinct slope changes in these curves represent various boundaries in the deep subsurface–namely, the Moho and the lithosphere-asthenosphere boundary (LAB). These slopes can be converted to depths, guided by Moho, LAB, and other geological constraints taken from previous surveys performed in the region. By examining how the depths of the Moho and the LAB change beneath the MEGA, it can be determined whether these structures are largely surficial in nature or are at least partially tectonically caused via crustal thinning. Preliminary gravimetric analysis indicates two main results. The first is that there are places in the MEGA where the Moho is surprisingly shallow (<30 km), especially when compared to the constraint values from previous surveys. This lends credence to the hypothesis that mantle upwelling is occurring in the region, causing crustal thinning. The second is that these grabens have a distinct high-gravity signature compared to the surrounding landscape, which lends evidence to high-density basaltic sheet diking occurring beneath them, due to the mantle upwelling and crustal thinning indicated by the shallower Moho depths.