In linearized delay time tomography the choice of a one‐dimensional reference model is very important for correct mapping of seismic anomalies. We demonstrate that the use of an inadequate background model results in artifacts in tomographic images which may give rise to erroneous interpretations. Particularly the absence or presence of upper mantle discontinuities in the reference model, influences the mapping of structures (e.g. subducting slabs) at the transition between upper and lower mantle. New tomographic images of the mantle below the Caribbean Region are presented. These show the extent of the Lesser Antilles subduction zone down to 600 km which is well below the seismic zone. A high velocity anomaly is imaged from the Mid American trench to lower mantle depths (1400 km).