Seismic reflections in normal fault zones in the Eastern Venezuelan basin usually appear distorted. Studies of reflections over fault structures delineated by drilling indicate that this is due to the similar effects of two entirely different phenomena: 1. True structural deformation of beds on the downthrown side. 2. Purely seismic distortion of reflections from underneath the fault. Analysis indicates that the structural deformations form an integral part of the fault zone; the purely seismic distortion is caused by passage of the wave through this zone of deformation.