Active displacement field in the Suez-Sinai area: the role of postseismic deformation

By means of a spherical viscoelastic model of co- and postseismic deformati on we compute the postseismic displacement associated with the November, 19 95, M-w = 7.2, Aqaba (Jordan) earthquake. We compare our results with the o bservational data obtained by a GPS campaign performed in a wide portion of Sinai between November 1997 and May 1998. Though the original purpose of t he campaign was to explain the tectonic features of the region, the displac ement values deduced from the GPS observations are hardly reconcilable with any of the proposed tectonic models of Sinai. Our hypothesis is that the d etected deformation field could be due more to the postseismic relaxation f ollowing the Aqaba earthquake rather than to tectonic movements. Our result s show that both GPS observational data and the postseismic simulations pre dict a compressional regime in the Gulf of Suez though the contraction dete cted by GPS is generally larger. The best agreement with the data is obtain ed for an asthenospheric and lower crust viscosity of 10(18) Pa s and an ab sence of aseismic afterslip on the fault plane. We conclude that the contri bution coming from the postseismic viscoelastic relaxation of the ductile s hallow layers following the 1995 Aqaba earthquake is likely to play an impo rtant role in determining the present deformation field in Sinai. The trans ient postseismic relaxation seems to play a more important role than the se cular tectonic deformation. (C) 2001 Elsevier Science B.V. All rights reser ved.