Is land subsidence increasing the exposure to sea level rise in Alexandria, Egypt?

Guy Woppelmann (1) , Gonéri Le Cozannet (2) , Marcello de Michele (2) , Daniel Raucoules (2) , Anny Cazenave (3) , Manuel Garcin (2) , Susan Hanson (4) , Marcos Marta (5) , Alvaro Santamaria-Gomez (1, 6)

1 LIENSs - LIttoral ENvironnement et Sociétés
2 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
3 LEGOS - Laboratoire d'études en Géophysique et océanographie spatiales
4 University of Southampton
5 IMEDEA - Institut Mediterrani d'Estudis Avancats
6 Observatorio de Yebes

Delta margins are subject to relatively high rates of land subsidence and have the potential to significantly exacerbate future changes in sea levels predicted by global warming models used in impact studies. Through a combined analysis of GPS and persistent scatterer interferometry data, we determine that most of the coastline of Alexandria has been subject to moderate land subsidence over the past decade (0.4 mm/year on average and up to 2 mm/year locally). This contrasts to previous studies that suggested subsidence in excess of 3 mm/year. Based on our findings, we infer that on multi-century to millennia timescales, land subsidence in the area of Alexandria is dominated by tectonic setting and earthquakes or gravitational collapse episodes of a growth fault, 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 layer.

Keywords: Sea level; Coastal subsidence; Alexandria; GPS; InSAR; tide gauge

Domains: Earth Sciences

Guy Woppelmann, Gonéri Le Cozannet, Marcello de Michele, Daniel Raucoules, Anny Cazenave, et al.. Is land subsidence increasing the exposure to sea level rise in Alexandria, Egypt?. Geophysical Research Letters, 2013, 40 (12), pp.2953-2957. ⟨10.1002/grl.50568⟩. ⟨hal-00825699⟩