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Animation of the principles of a drum-style vertical seismograph station that records up-and-down movement. Seismographs are designed so that slight earth vibrations move the instrument. The suspended mass remains at rest as the spring absorbs some of the motion. The stylus (pen) affixed to the mass, records the relative motion between itself and the rest of the instrument, thus recording the ground motion.
Animation of the vertical seismograph above slowed down to show compressive behavior of the P wave in the direction the wave is traveling and the shearing behavior of the S wave perpendicular to the direction of wave travel. Although the arrow shows gross movement, remember that this happens on a microscopic scale in the Earth.
Animation of the principles of a drum-style horizontal seismograph station that records back- and-forth (N–S, E–W) movement. The suspended mass remains at rest as the spring and pivoting knife absorb most of the motion during an earthquake. The instrument shifts back and forth due to the oblique travel direction of the P wave and the shearing movement of the S wave. The stylus (pen) affixed to the mass, records the relative motion between itself and the rest of the instrument, thus recording the ground motion.
Movie clip of an actual seismograph drum at the Hawaiian Volcano Observatory recording a small local earthquake. Although most Observatory seismometers are now computerized, the rotating drums are still used in displays for visitors. (Used with permission from Volcano Video Productions.)
Animations and videos are made in partnership with Earthscope, USGS, and Volcano Video & Graphics.
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