Crustal attenuation across the East African plateau in Tanzania, an area of uplifted and rifted Precambrian crust, has been investigated using seismic data from regional earthquakes recorded by the 1994-1995 Tanzania broadband seismic experiment. We use 1 Hz Lg coda waves from the 17 events, together with the energy flux model of Frankel and Wennerberg (1987), to obtain estimates of intrinsic (QI) and scattering (QS) attenuation for East Africa. QI values across the plateau are fairly uniform, ranging from a low of ~300 to a high of ~600. QI values for the Tanzania craton, in the middle of the plateau, are similar to those for the mobile belts, which form the sides of the plateau. QI of 300 to 600 is somewhat lower than the average crustal Q for Precambrian terrains elsewhere. Heat flow from the Tanzania craton and surrounding mobile belts is not elevated; therefore, we attribute the lower-thanaverage Q values not to elevated crustal temperatures, but instead to rift faults in the crust that are interconnected and filled with fluids. QS ranges from ~1000 in the mobile belts and along the eastern margin of the Tanzania craton to ~2200 in the north central part of the plateau just south of Lake Victoria.We attribute the variability in QS to scattering of Lg by surface topography, in particular, rift basins along the eastern side of the plateau.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology