Upper Mantle Anisotropy beneath Northern Algeria from Shear-Wave Splitting Anisotropy beneath Northern Algeria

Abstract

Northern Algeria is a large region in the north-western of Africa, lying on the collision boundary between the African and Eurasian plates. Few studies on Lithosphere and Mantle deformation have been conducted in this region. To better understand the seismic anisotropy patterns beneath this area, we used data from 17 broadband stations installed in Tellian and the Saharan atlases using the SKS shear wave splitting method by processing hundreds of teleseismic events. To estimate the seismic anisotropy, two parameters were calculated, the fast polarization direction and the delay time for each station-event pair. The results show that the seismic anisotropy can be described by two main orientations, ENE-WSW follows the general trend of the Saharan Atlas, particularly in the central and western parts, and ESE-WNW follows the Hodna Mountains in south-eastern Algeria. Our results show that the anisotropy can be explained by single and heterogeneity in the anisotropic structure, where the measurements are very scattered, and the delay time and fast direction changed with the events backazimuth. In the ABSD, CBBR and CDCN stations, which lie in the arc between the Sahara Atlas and the Aurès Mountains, the origin hypothesis of the seismic anisotropy can be linked to the existence of a detached slab. Moreover, in ABZH, OKGL and EARB stations located in the Kabylide and Western regions, it can be associated with the Gibraltar slab. Both slabs sinking in the African margin mantle were previously imaged by seismic tomography. For the remaining stations, the single-layer best explains the observed seismic anisotropy from their regular fast polarization direction. The comparison of the obtained fast directions with GPS measurements shows that anisotropy fast axes are nearly perpendicular to the convergence direction between the African and Eurasia plates.