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Freie Universität Berlin (2004)

A RECEIVER FUNCTION STUDY OF THE CRUST AND UPPER MANTLE ACROSS THE DEAD SEA TRANSFORM

Mohsen, Ayman

Titre : A RECEIVER FUNCTION STUDY OF THE CRUST AND UPPER MANTLE ACROSS THE DEAD SEA TRANSFORM

Auteur : Mohsen, Ayman

Université de soutenance : Freie Universität Berlin

Grade : PhD, FB Geowissenschaften, 2004

Résumé
The Dead Sea Transform (DST) fault, formed about 20 M.Y. ago is a major structural feature, which demarcates the two tectonic plate boundaries, Arabian and African plates and it remains a stable platform almost since the formation of these plates in the late Proterozoic. The tectonic stability of this region was only recently (20 M.Y. ago) interrupted by the formation of the DST with a left lateral motion of about 107 km. The general strikes of this fault is from N15°E to N20°E and extends from Red Sea northwards along Wadi Araba, Dead Sea, Jordan Valley, lake Tiberias and central Lebanon over 1100 km to the continental collision zone in the Taurus-Zagross mountain belt. To know the nature of the crust in this area and also the nature of this mega geo-feature a number of geophysical studies have been done under the multinational geophysical project (DEad SEa Rift Transect) started in Feb. 2000, to study the crustal and the upper mantle of the DST. Under this project the passive source seismic studies were also been carried out to deciphere the crustal structure as well as the mapping of the deep mantle transition zones. A temporary network consisting of broadband and shortperiod seismic stations was set up in the area for one year beginning in April 2000 as part of the multidisciplinary DESERT project. The aperture of the network is approximately 250 km in NW-SE direction from the Mediterranean Sea crossing Wadi Araba fault into the highland area in Jordan and 150 km in SW-NE direction between the Dead Sea and the Red Sea along Wadi Araba fault. In the present work, the receiver function method has been applied to three component passive source data to investigate seismic discontinuities in the crust down to the upper mantle . The seismic structure of this region has been presented in a unified way and the results have been discussed in the light of the other geophysical studies carried out in this region. Receiver function analysis utilises teleseismic body waves to retrieve the crustal and lithospheric structures beneath recording stations. The waveforms arriving at the recording stations have the effects of earthquake source, the earth’s structure in the vicinity of both the source and station and mantle propagation effects. Source equalization is a technique to explore crustal and upper mantle structure at the receiver sites removing the source and mantle path effects. On application of receiver function methodology on the three component data of this region it has been found that the Moho depth increases smoothly from about 30 km west of the DST to about 35 km underneath the DST and continues to deepen to about 40 km in the eastern most stations along the controlled source line. East of the DST the natural source data indicate a shallower Moho to the north and south than directly along the controlled source line. This indicates that the crust is not simply thickening from west to east but has a much more 3 D complicated structure. The study shows that the crustal structure in the west and east of the Araba fault is different indicating that the Araba fault is of deep seated nature and divides the whole region into two parts at least down to the Moho. The P-to-S converted phases from 410 and 660 km discontinuities are delayed by 2 s with respect to IASP91 global reference model, indicating that the upper mantle above 410 km is 3-4% slower than the standard earth model. This could mean that the upper mantle in the region is still influenced by several geodynamical processes involving rifting, uplift and magmatism.

Mots clés : seismology, receiver function, crust, upper mantle, discontinuties

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Page publiée le 22 juin 2013, mise à jour le 2 novembre 2018