Moho depth variation and shear wave velocity structure in northern Algeria from joint inversion of P-wave receiver functions and Rayleigh wave dispersion data

Abstract

SUMMARY In this work, the Moho depth and the velocity structure of the crust and upper mantle beneath broad-band seismic stations of the Algerian broad-band seismic network are investigated. Teleseismic P-wave receiver functions jointly inverted with Rayleigh wave dispersion curves obtained from local earthquakes have been used. The seismic stations are located in different geological settings including the Tell Atlas, High Plateaus and the Saharan Atlas. The crustal thickness and the Vp/Vs ratio are first derived by the H–κ stacking method of receiver functions. The inversion results show the variation in Moho depth in the different geological contexts. The shallowest depths of the Moho (∼20–30 km) are estimated along the Algerian continental margin and Tell Atlas. In the High Plateaus region, the Moho depths vary from 30–36 km, whereas the deepest Moho depths are found in the Saharan Atlas (36–44 km). Two-layer crust is observed in the whole study area. In the upper crust, ∼8–14 km thick, the average shear wave velocity is ∼3.0 km s−1. The lower crust of about 12–30 km thick has an average shear wave velocity that ranges between 3.4 and 3.8 km s−1. The lower crust is thicker than the upper crust particularly in the Saharan Atlas. The upper mantle shear wave velocity varies from 4.1 to 4.5 km s−1 maximum and is stable, generally, below ∼60 km depth. Two low-velocity zones are clearly observed particularly in the eastern part of the Tell Atlas and the High Plateaus. The first one about 10 km thick is in the lower part of the lower crust and the other one is in the upper mantle between 40 and 60 km depth. The obtained results are in accordance with the previous results found in the region, particularly those using land gravity and seismic data. As the first estimate of the Moho depth from earthquake data in northern Algeria, using the receiver function method, this study sheds new light on the crustal structure and the Moho depth in this region of the world.