SEISMIC WAVE ATTENUATION IN THE LITHOSPHERE OF THE NORTH TANZANIAN DIVERGENCE ZONE (East African rift system)
A.A. Dobrynina1, J. Albaric2, A. Deschamps3, J. Perrot4, R.W. Ferdinand5, J. Déverchère4, V.A. San’kov1,6, V.V. Chechel’nitskii7
1Institute of the Earth's Crust, Siberian Branch of Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
2University of Bourgogne-Franche Comte, Lab. Chrono-environnement, Besançon, France
3Université Côte d'Azur, CNRS, OCA, IRD, Géoazur, France
4Brest University (UBO), CNRS UMR 6538 Géosciences Océan, IUEM, Plouzané, France
5University of Dar es Salaam, Geology Departmen, P.O. Box 35052, Dar es Salaam, Tanzania
6Irkutsk State University, ul. Karla Marksa 1, Irkutsk, 664003, Russia
7Baikal Branch of the Geophysical Survey, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
Keywords: Seismic quality factor, attenuation, coda, North Tanzanian divergence, East African rift system
Abstract
The seismic effective quality factor ( QC ) and its frequently dependences or the frequency parameter ( n ) and attenuation coefficient (δ) for the Earth’s crust and upper mantle of the North Tanzanian divergence zone (East African rift system) were estimated from an analysis of the earthquake coda waves recorded in the SEISMO-TANZ’07 French-Tanzanian seismic experiment. The QC values increase and the n and δ values decrease with increasing frequency and length of the lapse time window. This behavior of the attenuation parameters may be evidence that the degree of heterogeneity of the lithosphere decreases with depth. Comparison of the depth variations in the attenuation coefficient δ and the frequency parameter n with the velocity structure of the region shows that there is a distinct change in the behavior of seismic wave attenuation at velocity discontinuities. The obtained attenuation parameters were compared with the same parameters obtained in our previous studies for other continental rift systems - the Baikal rift system (Eurasia) and the Basin and Range Province (North America).
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