Same earthquake, different stations; why do the seismograms look different?
We use a cow and a tree in this narrated cartoon for fun and to emphasize that seismic waves traveling away from an earthquake occur everywhere, not just at seismic stations. A person would feel a large earthquake only at station A near the epicenter. Stations B, C, D, and the cow are too far from the earthquake to feel the seismic waves. Both the scale of the buildings (and cow) and the amplitude of the movements are exaggerated. The cartoonish amplified ground motions show the compressive (up-down in this case) P wave, the shearing (back-forth) S wave, and the rolling surface wave motions recorded by sensitive instruments. Notice that Station D does not record an S wave because shear waves cannot travel through Earth's liquid outer core. One seismic station can give information about how far away the earthquake occurred, but yields little other information. The cartoonish amplified ground motions show the compressive P wave, the shearing S wave, and the rolling surface wave motions recorded by many stations with their characteristic seismograms. See also Travel-time curves.
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ANIMATED GIFS (MP4 FORMAT): short segment of entire animation available as Optional Download.
- Seismic stations at varying distances from a large earthquake have signature seismograms
- Seismic stations record the compressive, shearing, and rolling behavior of different seismic waves
- Seismograms indicate the travel time of P and S waves
- Seismograms yield information about the shadow zones