Crustal and upper mantle structure of northern Algeria inferred from a 3-D inversion of teleseismic tomography

Abstract

The northern Algeria forms the southern edge of the Western Mediterranean Sea that formed within the zone of convergence between the African and Eurasian plates. It represents a key area in the Mediterranean formation where controversial kinematic and geodynamical models are proposed. The current structure of northern Algeria is the result of the geodynamic evolution that occurred in the western Mediterranean. Several tomographic studies revealed the presence of velocity anomalies beneath the south of the western Mediterranean region. Namely, these anomalies suggest the existence of abnormally cold material in the asthenosphere, interpreted as the trace of subducted plunging panels (slab). Unfortunately, the lack of suitable data remains the main limit confronted by most tomographic studies in the northern Algeria, which remains to date one of the poorly studied regions in the western Mediterranean. During the recent decades, the seismological network in northern Algeria has significantly developed, giving rise to a significant increase in the amount of information given by the network database. This development motivated us to investigate the crust and the upper mantle structure beneath the northern Algeria using a non-linear teleseismic tomography method. An overall of 29 stations distributed along the northern part of Algeria have been used to collect 11018 P-waves from 2847 earthquakes recorded over ten years. The proposed model suggests the presence of high-velocity anomalies along of the northern Algeria. We interpreted these abnormal anomalies as a slab teared into two panels. A central segment bending along the Atlasic massif of Hodna and plunging under the Lesser Kabylia. The second segment at the North-East, shifted to the north plunging towards the NE. A series of Tellian high-velocity anomalies axes mark the limit between the African and the Eurasian plate. The south eastern region covered by our model (Aurès massif) is characterized by a low-velocity anomaly potentially linked to the remnant of the Mesozoic rifting.