Chester R. Longwell and Richard Foster Flint, Introduction to Physical Geology

CRITICAL PATHS OF SEISMIC WAVES SENT OUT FROM AN EARTHQUAKE FOCUS O, IN RELATION TO THE CORE BOUNDARY AND THE SHADOW ZONE

Behavior of the P and S waves in their downward course is shown. Stations farther away receive no S wave, and a zone between 103° and 143° from the epicenter shows neither P nor S records. In this 2,750 mile-wide "shadow zone," only the L waves and complicated reflections are recorded. The abrupt disappearance of the S wave indicates a change from solid to fluid state. P waves continue through the core, but their velocity drops abruptly from approximately 8 m/s to 5 m/s.