ESTIMATES OF CRUSTAL AND LITHOSPHERIC THICKNESS IN SUB-SAHARAN AFRICA FROM S-WAVE RECEIVER FUNCTIONS

Estimates of crustal and lithospheric thickness beneath ten permanent seismic stations in southern, central, and eastern Africa have been obtained from modeling S-wave receiver functions (SRFs). For eight of the examined stations, the Moho depth estimates agree well with estimates from previous studies using P-wave receiver functions (PRFs). For two stations, TSUM and BGCA, previous PRF estimates are not available, and our results provide new constraints on the Moho depth, indicating crustal thicknesses of 35 and 40 km, respectively. SRFs from four stations, BOSA, SUR, FURI, and ATD, display clear S-to-P (Sp) conversions from the lithosphere-asthenosphere boundary (LAB), corresponding to lithospheric thicknesses of 155, 140, 80, and 34 km, respectively. As expected, thicker lithosphere is observed beneath the Precambrian Kaapvaal Craton (station BOSA) and the Namaqua-Natal mobile belt (station SUR) and thinner lithosphere is observed beneath the edge of the Ethiopian rift (station FUR!) and the Afar Depression (station ATD). The thinner lithosphere beneath the two latter stations is consistent with the transition from continental to oceanic rifting at the Afar triple junction. For the remaining stations, bootstrap error estimates indicate that the Sp conversion from the LAB cannot be well resolved, calling into question interpretations of lithospheric structure in previous SRF studies using data from these same stations.