Lithospheric structure of the Arabian Shield from the joint inversion of receiver functions and surface-wave group velocities

Abstract

We estimate lithospheric velocity structure for the Arabian Shield by jointly modeling receiver functions and fundamental-mode group velocities from events recorded by the 1995–1997 Saudi Arabian Portable Broadband Deployment. Receiver functions are primarily sensitive to shear-wave velocity contrasts and vertical travel times, and surface-wave dispersion measurements are sensitive to vertical shear-wave velocity averages, so that their combination bridge resolution gaps associated with each individual data set. Our resulting models correlate well with the observed surface geology; the Asir terrane to the West consists of a 10-km-thick upper crust of 3.3 km/s overlying a lower crust of 3.7–3.8 km/s; in the Afif terrane to the East, the upper crust is 20 km thick and has an average velocity of 3.6 km/s, and the lower crust is about 3.8 km/s; separating the terranes, the Nabitah mobile belt is made of a gradational upper crust up to 3.6 km/s at 15 km overlying an also gradational lower crust up to 4.0 km/s. The crust–mantle transition is found to be sharp in terranes of continental affinity (east) and gradual in terranes of oceanic affinity (west). The upper mantle shear velocities range from 4.3 to 4.6 km/s. Temperatures around 1000 °C are obtained from our velocity models for a thin upper mantle lid observed beneath station TAIF, and suggest that the lithosphere could be as thin as 50–60 km under this station.