Blind and surface faulting during large and moderate earthquakes deduced from InSAR in Algeria and Morocco: Insights for the active deformation along the plate boundary in North Africa
Samir Belabbes(1) , Mustapha MEGHRAOUI(2)
, and Ziyadin CAKIR(2)
IPG Strasbourg, UMR7516,
5 rue René Descartes,
(2) IPG Strasbourg, UMR 7516, 5 rue René Descartes, 67084 Strasbourg, France
We study recent earthquakes along the plate boundary in North Africa using InSAR. The selected large to moderate earthquakes of Mascara (18 August 1994, Mw 5.8), Ain Temouchent (22 December 1999, Mw 5.7), Zemmouri (21 May 2003, Mw 6.8) and Al Hoceima (26 May 1994, Mw 6.0; 24 February 2004, Mw 6.5) belong to a narrow strip, parallel to the plate boundary, in the Tell Atlas and Rif Mountain ranges. The surface deformation of earthquakes mapped by InSAR, and related rupture at depth obtained from elastic models of dislocation, are consistent with late Quaternary tectonic investigations. We constructed numerous interferograms using Envisat and ERS SAR data acquired both in the ascending and descending passes of the satellites with SRTM digital elevation model for the removal of the topographic contribution. Although the possibility of producing fringes associated with moderate magnitudes (Mw<6) is low, the selection of image pairs and the shallow faulting allowed us to obtain interferograms with up to 4 fringes across the epicentral region of the Ain Temouchent earthquake. In the absence of surface faulting and reliable maps of aftershocks distribution, our InSAR results contribute significantly to the identification and characterisation of seismogenic faulting. The correlation with the morphology and seismic rupture at depth is consistent with previously mapped active folds and inferred seismic moments. Furthermore, the seismic moment summation deduced from InSAR is directly comparable to the seismic strain release and rate of convergence as obtained from global model of plate tectonics and local GPS networks. The interferograms of recently earthquake ruptures also provide with the definition of dormant nearby fault segments that constitute possible sites of future earthquake sources. The InSAR analysis related with moderate to large earthquakes in North Africa becomes a prerequisite for any seismic hazard assessment along the plate boundary.