Appendix A – Construction of the Bouguer gravity map

Shipboard gravity coverage of the eastern Mediterranean is different for various parts of the sea, but satellite altimetry gives an excellent possibility to fill the gaps within the marine gravity measurements. Satellite gravity data are collected by a radar altimeter mounted aboard an earth-orbiting satellite (Smith and Sandwell, 1997). The satellite data have at least two important advantages: the data are consistent and are public domain. This methodology and numerous examples of using the radar altimetry are described in details in the scientific literature (e.g., Small and Sandwell, 1992; Neumann et al., 1993; Sandwell and Smith, 1997; Smith and Sandwell, 1997; ten Brink et al., 2002; Sandwell et al., 2003; Brodscholl et al., 1992; Sandwell and Smith, 2005a, b, 2009; Harmon et al., 2006). 
For the eastern Mediterranean the free-air gravity values were extracted from the last public domain version of the satellite altimetry (Sandwell and Smith, 2005a, b) with a spatial resolution of 1-min.  
The topography and bathymetry data derived from SRTM30_PLUS: data fusion of SRTM land topography with measured and estimated seafloor topography (ftp://topex.ucsd.edu/pub/srtm30_plus/). Ocean data are based on the Smith and Sandwell global 2-minute grid between latitudes ± 72º.   
The obtained free-air gravity has been correlated with prominent bathymetric features of the region, and in particular the Eratosthenes seamount. In order to suppress the gravity influence of sea flow relief, we calculated the gravity effect of the water layer in 3-D mode. The calculated values were added to the free-air values to compile the Bouguer gravity map. This procedure allows not only applying the Bouguer correction but the terrain correction also. Therefore the resulting map (Fig. 10) is the complete Bouguer gravity map.
Shipboard data, in comparison with satellite data, have a typically higher resolution in well-studied areas, but provide much less overall coverage. Therefore, data of two dense shipboard gravity surveys in the eastern Mediterranean area provided benchmarks for testing the 2-D resolution and accuracy of the satellite measurements. The first survey was located close to the Israeli coastline, where new geophysical data sets include ~12,000 km of 2-D seismic reflection lines and several high-resolution 2-D and 3-D surveys, which included also gravity and magnetic measurements (Gardosh et al., 2008). The second survey was carried out south and west of Cyprus (Toulin, 2005). Based on these surveys the reliability and accuracy of the satellite gravity for the eastern Mediterranean areas were found to be good.

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