A major unresolved question in global seismology, the important implications for Earth structure and dynamics, remains the detection and accurate characterization of discontinuities of the transition zone, the jumps on elastic parameters are known approximately, as well as their average locations, while for others we have merely indirect evidence of their existence. We propose to investigate the structure of the transition zone, with particular emphasis on the characterization of discountinuities. To achieve this, we have developed a procedure for inferring the properties of a discontinuity from a sparse network of three commponent stations. This uses a hybrid reflectivity - WKBJ approach to the systematic generation of all phases of non-negligible amplitude that interact with a parti- cular boundary, combined with optimal estimates of body wave vector displacement to constrain the observed ray parameter. By incorporating a variety of reflected and converted phases for many events, at different depths and with a range of ray para- meters, we can separate the effects of jumps in wave speeds and density, while by using broad band data we can also estimate thickness.
