Investigation of crust structure of Tanzania by body-wave ray tracing

Analysis of earthquake body wave phases from both regional and local events which occurred in Tanzania from 1966 to 1992 and recorded by regional stations in Nairobi (Kenya) and Lwiro (Zaire) and a local network in Mbeya (Tanzania) was carried out. Travel time graphs for events located in the western rift and recorded at Lwiro station show velocities for body wave phases as follows: Pg of 6.0 km/s, Pb of 6.6 km/ s, Pn of 7 . 8 km/s and Sn of 4.4 km/s. Events located in the Eastern branch and recorded at Nairobi station show a Pn phase velocity of 7.6 km/s. In both regional stations, a low velocity Pn phase stops to show up for at epicentral distance above 500 km and 700 km for events traversing the eastern and the western rift respectively. A crustal structure model has been derived for the area within Mbeya network based on travel time data from first arrival P and S phases. The models consist of five layers overlying half space. Velocities of P phases obtained are as follows: Velocity (km/s) Depth (km) 5.6 3.0 6.0 9.0 6.25 13.0 6.4 20.0 6.6 28.0 7.8 P phase velocities for the model obtained agree with the ones obtained from regional station at Lwiro. The crust structure obtained is related with the structure of the continental drift