Seismological investigation of the Bangui magnetic anomaly region and its relation to the margin of the Congo craton

Abstract

Inversion of teleseismic travel times of P-waves recorded by a temporary linear array of seismological stations has been carried out in order to investigate the deep P-wave velocity structure in the Central African Republic in a region where a large magnetic anomaly—one of the largest occurring over a stable continent—has been revealed by satellite and surface surveys. Because of the good azimuthal coverage of seismic sources, it turned out that most of blocks are sampled by rays crossing in widely different directions. Lateral inhomogeneities strongly bias 2-D inversion and explain why 3-D inversion improves the fit of the data. Structural variations persist down to a depth of 160 km. Crustal thickness is about 40 km. Lateral inhomogeneities may be related to the northern margin of the Congo craton where up to 4% higher velocities are observed. The similar patterns of the Bangui magnetic anomaly and of the seismic velocity distribution suggest a close relation between the two. The abnormal magnetic field could be due to a deep structure with a higher susceptibility.