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Earthquake!! The P wave propagates at ~6 km/sec in rock with particle motions that are parallel to the direction of propagation. The S wave is slower at 4 km/sec and propagates with particle motions that are perpendicular to the direction of propagation. When we record these waves, the gap between the P wave and the S wave provides information about how far away the earthquake occurred from the seismograph.
Narrated by Michael Hubenthal, Incorporated Research Institutions for Seismology
Animated by Jenda Johnson, Earth Sciences Animated (for IRIS)
