LITHOSPHERIC STRUCTURE OF NORTHERN AFRICA AND WESTERN EURASIA

Although much progress has been made over the last few decades towards understanding the structure of the Earth, many questions regarding the details of Earth's lithospheric structure remain unanswered. The primary goal of this study was to gain a better understanding of upper and lower continental crustal composition and structure to improve our knowledge of the tectonic evolution of the Earth. To contribute this goal, we focused on the estimation of first order seismic structure using receiver functions, and the construction of a library of shear-velocity structures in the vicinity of seismic stations across western Eurasia and northern Africa using receiver functions and tomography based surface-wave dispersion estimates.

We used one hundred and seventy one stations recording a total of about 6,000 teleseismic events producing more than 100,000 seismograms. The distribution includes 78 stations in the Middle East and Asia, 57 stations in Europe, and 36 stations in central and northern Africa. We have examined receiver functions for 119 stations with the best data for the period of 1990-2004 and applied the receiver function stacking procedure of Zhu & Kanamori (2000, JGR) to estimate Poisson's ratio and crustal thickness. The structures are classified into five tectonic environments, explicitly shields, platform, Paleozoic orogenic belts, Mesozoic-Cenozoic orogenic belts, and rifts based on Condie's (1989) global classifications. The results show a slightly lower value of Poisson's ratio σ = 0.25 for shields compared to the orogenic-belts with σ = 0.26. Crustal thickness ranges from 32-47 km with an average of 38 km and standard deviation of 3 km for the shields. The less well sampled platforms show a wider distribution of crustal thickness, ranging from 30-58 km with an average 42 km and a standard deviation of 9 km. Orogenic regions the largest variation in crustal thickness with values from 20 to 55 km and standard deviations in the range of 8-10 km. We combined observations obtained in this study with receiver functions results from other published analysis. In total, we have integrated observations from 606 stations located in different geologic settings. The compiled results show a value of σ = 0.26 for Poisson's ratio and H = 39 km for crustal thickness in shields and platforms, and σ = 0.26-0.27 with H = 35-37 km for the orogenic belts.

References Cited:

Zhu, H. & Kanamori, H, 2000. Moho depth variation in southern California from teleseismic receiver functions. J. geophys.Res., 105, 2969-2980