Fig. 7

Ray paths (top) and calculated travel times (bottom) in the Sohl and Spohn (1997) model A, with (right) and without (left) an inner core. The inner core’s properties are only scaled version of the Earth’s inner core and only meant to be indicative of the change in the travel time curves, and not otherwise physically justified. The horizontal axis is distance from an earthquake source at 0, measured in degrees of arc around the planet. The lag time until an arrival is seen is the time plotted on the vertical axis. Each type of seismic wave arrival traces a continuous path as a function of distance. Curves with positive slopes travel directly between the source and receiver (along the minor arc, to distances <180°). Curves with negative slopes travel the long way around the sphere (along the major arc to distances >180°). Each wave type is labeled with its name (see the “Appendix” section for nomenclature). The core’s low wavespeeds with respect to the mantle cause a P-wave arrival shadow, the gap between P and PKP between ∼120– ∼180° (top left). The main difference is that the inner core reflection PKiKP (and PKIKP) illuminates the shadow region when an inner core is present (top right). SKS and SKKS illuminate the core, but the ranges of the SKS (>160°) and SKKS (>300°) arrivals are truncated by the presence of an inner core