Land Subsidence on Alexandria observed by SAR Interferometry Techniques, Implications for Exposure to Sea Level Rise
Wöppelmann, Guy1; Le Cozannet, Gonéri2; de Michele, Marcello2; Raucoules, Daniel2; Cazenave, Anny3; Garcin, Manuel2; Marcos, Marta4; Santamaría-Gómez, Alvaro5
1LIENSs, Université de La Rochelle, FRANCE; 2BRGM, FRANCE; 3LEGOS, FRANCE; 4IMEDEA, SPAIN; 5IGN, SPAIN
In this poster we investigate the ground surface deformation on Alexandria (Egypt). Delta margins are overall subject to relatively high rates of land subsidence, aggravating the exposure of port cities to large storm surges and rising sea levels predicted by global warming models. Through a combined analysis of GPS and persistent scatterers interferometry data (PSI), we determine that Alexandria coastal region is subject to moderate land subsidence of 0.4 mm/year on average over the past decade, in contrast to previous studies suggesting subsidence in excess of 3 mm/year. The PSI results are assessed against independent satellite altimetry minus tide gauge data within 0.5 mm/year-level precision. Based our geodetic findings, we infer that on multi-century to millennia timescales land subsidence in the area of Alexandria is much dominated by tectonic setting and earthquakes, whereas on shorter inter-seismic decadal to century timescales subsidence rates are likely steady and moderate, in agreement with natural compaction and dewatering of the observed Holocene sediment thickness.
Linear line of sight (LOS) velocities over the period 2002-2010 from the PSI results are with respect to the GPS station. Positive velocities indicate site uplift, whereas negative velocities indicate subsidence