Finite deformation and displacement fields on the southern yemen margin using satellite images, topographic data and a restoration method

Abstract

Geological interpretations of processed satellite images and structural field measurements were used to calculate the amount of extension and the finite displacement field of two stretched areas located on the northern margin of the Gulf of Aden, in Yemen. This calculation was done by a comparison between the deformed and the undeformed states of each studied area. The structural setting established from satellite-image interpretations and fieldwork yields a detailed geometry of the deformed state. The undeformed state was reconstructed from reference layers chosen on satellite images from folded and faulted geological markers. The strike and dip of those layers were computed directly from dip indicator measurements, identified on three-dimensional (3D) realistic views of the sites (derived from SPOT stereoscopic views and topographic data) and controlled by field measurements. From the previous structural data, a numerical model of the deformed state was prepared with respect to the structural setting. The two stretched areas were then restored to their undeformed state successively by (1) an unfolding method (use of the UNFOLD program on each folded piece bounded by faults), and (2) a best-fit method (fitting along the boundary of the unfolded pieces). The comparison between the deformed and undeformed states leads to quantifying the amount of strain and to establishing the total finite displacement field. The results point to differences in the amount of extension and in the finite displacement field between the two areas studied. Within the regional context of the Afar triple junction kinematics, this leads to the conclusion that there was an early extensional tectonic phase recorded on the southern Yemen margin, probably linked to the earlier opening of the Gulf of Aden.