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New constraints on crustal structure in eastern Afar from the analysis of receiver functions and surface wave dispersion in Djibouti

2006; Geological Society of London; Volume: 259; Issue: 1 Linguagem: Inglês

10.1144/gsl.sp.2006.259.01.19

2041-4927

M. T. Dugda, A. Nyblade,

earthquake and tectonic studies

Abstract Crustal structure beneath the GEOSCOPE station ATD in Djibouti has been investigated using H -κ stacking of receiver functions and a joint inversion of receiver functions and surface wave group velocities. We obtain consistent results from the two methods. The crust is characterized by a Moho depth of 23 ± 1.5 km, a Poisson’s ratio of 0.31 ± 0.02, and a mean V p of c. 6.2 km s −1 but c. 6.9–7.0 km s −1 below a 2–5 km-thick low-velocity layer at the surface. Some previous studies of crustal structure for Djibouti placed the Moho at 8 to 10 km depth, and we attribute this difference to how the Moho is defined (an increase of V p to 7.4 km s −1 in this study vs. 6.9 km s −1 in previous studies). The crustal structure we obtained for ATD is similar to crustal structure in many other parts of central and eastern Afar. The high Poisson’s ratio and V p throughout most of the crust indicate a mafic composition and are not consistent with models invoking crustal formation by stretching of pre-existing Precambrian crust. Instead, we suggest that the crust in Afar consists predominantly of new igneous rock emplaced during the late syn-rift stage where extension is accommodated within magmatic segments by dyking. Sill formation and underplating probably accompany the dyking to produce the new and largely mafic crust.