Upper mantle Q and thermal structure beneath Tanzania, East Africa from teleseismic P wave spectra

Abstract

We measure P wave spectral amplitude ratios from deep-focus earthquakes recorded at broadband seismic stations of the Tanzania network to estimate regional variation of sublithospheric mantle attenuation beneath the Tanzania craton and the eastern branch of the East African Rift. One-dimensional profiles of QP adequately explain the systematic variation of P wave attenuation in the sublithospheric upper mantle: QP ∼ 175 beneath the cratonic lithosphere, while it is ∼ 80 beneath the rifted lithosphere. By combining the Q P values and a model of P wave velocity perturbations, we estimate that the temperature beneath the rifted lithosphere (100-400 km depth) is 140-280 K higher than ambient mantle temperatures, consistent with the observation that the 410 km discontinuity in this region is depressed by 30-40 km. Copyright 2004 by the American Geophysical Union.