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Our transcription: As geophysicists probe deeper into the Earth's interior, the properties of the two types of seismic waves provide clues about what the core of this planet must be like. When a large earthquake occurs, seismograph stations around the world record the arrival of its "P" and "S" waves, but for stations slightly more than half the distance around the earth from the focus of the quake, P-waves are not recorded. This region is called the P-wave shadow zone. At almost the opposite point on the Earth's surface, the "P" waves reappear. The shadow zone exists because the waves are refracted as they pass through the boundary between the mantle and the core and are diverted from their original paths.
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