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When a magnitude 6.8 earthquake shook Olympia, Wash., in 2001, shopowner Jason Ward discovered that a sand-tracing pendulum had recorded the vibrations in the image above.
Seismologists say that the “flower” at the center reflects the higher-frequency waves that arrived first; the outer, larger-amplitude oscillations record the lower-frequency waves that arrived later.
(Source: futilitycloset.com)
