Shear source multiazimuth near‐ and far‐offset vertical seismic profiles, Asal Rift, Republic of Djibouti

Abstract

A three‐component borehole seismic data set obtained in the Asal rift zone shows that azimuthal anisotropy may be present with the fast propagation direction aligned with the present‐day rift axis. This is seen on the near‐ and far‐offset vertical seismic profile (VSP) data from the two source points lying parallel to the rift axis. The third orthogonal source point gives propagation times characteristic of near‐horizontal paths along the detected slow direction. The reflected VSP wave field contains both P and S energy. The main P and S reflections correlate well and correspond to thin clay and siltstone layers interspersed within the lava flow series. Some evidence exists for a change with depth of the amount or direction of the anisotropy found in the uppermost 400 m.