Overview of ray paths and location of events, stations, and bounce points of the precursor data set considered in this study. (a) Ray paths of the SS phase and underside reflections at the 410 (S410S) and 660 (S660S) for an event (blue star) at 35 km depth and a station (orange triangle) at 130° epicentral distance for model IASP91 (red profile; Kennett & Engdahl 1991). The insets show details of the bounce point region near the 410 and 660 discontinuities (dotted lines) and a synthetic SS waveform with prominent SS, S410S and S660S phases (blue wiggles; cf. dotted lines). (b) Global configuration of stations (orange triangles) and events (blue stars) used in the present study. Plate boundaries from USGS are plotted in magenta. (c) The grey-shaded map illustrates the logarithmic bounce point density, where white/black areas indicate low/high density, respectively. Plotted on top are the outlines of the Voronoi cells (blue grid) used for binning waveforms and the respective mean bounce point locations (orange).