The ScS precursors for the study of the lowermost mantle

The exploration of the lowermost-mantle structures by means of body wavefor m modeling allows the small-scale detection of heterogeneity and anomalous layers. In some regions the D " layer presents a discontinuity at its top t hat seems to be a local feature. This anomalous reflector may be recognized by the detection of a small core-reflected phases precursor. These studies may present different order of problems. The main difficulties, are connec ted to the identification of the precursor and its association to the D " r egion. Misunderstandings often result because of phases produced by heterog eneity and anisotropy along and in the vicinity of the ray paths, in the cr ust and mantle structures. These complexities are increased when large data set and recording arrays, which may facilitate the waveform analysis, are n ot available. In this paper we discuss the body waveform modeling of lower- mantle phases for the study of the D " with particular focus on the case of sparse data with only few events and stations available.