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USGS CMG InfoBank: Seismic Wave Velocities

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Comment: 06:46 - 07:36 (00:50)
Source: Annenberg/CPB Resources - Earth Revealed - 9. Earthquakes
Keywords: earthquake, "P-wave", "S-wave", "primary wave", "secondary wave", epicenter, "Richard Hazlett"

Our transcription: This difference in velocity between "P" and "S" waves is highly significant.
It enables seismologists to calculate the precise location where an earthquake has occurred.
If one lies close to the epicenter of an earthquake, the "P" and the "S" waves will not have had enough time really to become separate from one another as they travel through the Earth, and when they arrive all at once, the earthquake is felt as a sharp jolt.
If, however, one lies at a great distance from the epicenter, the "P" waves will have far out-raced the "S" waves, and so arrive much earlier than the "S" waves do.
The time interval between the arrival of the "P" and the "S" waves thus is a function of the distance to the source, the epicenter.

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