[sahyz-muh-graf, -grahf, sahys-]
any of various instruments for measuring and recording the vibrations of earthquakes.

1855–60; seismo- + -graph

seismographic [sahyz-muh-graf-ik, sahys-] , seismographical, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
seismograph (ˈsaɪzməˌɡrɑːf, -ˌɡræf)
Also called: seismometer an instrument that registers and records the features of earthquakes. A seismogram () is the record from such an instrument

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
seismograph   (sīz'mə-grāf')  Pronunciation Key 
An instrument that detects and records vibrations and movements in the Earth, especially during an earthquake. Most seismographs employ a pendulum mounted within a rigid framework and connected to a mechanical, optical, or electromagnetic recording device. When the Earth vibrates or shakes, inertia keeps the pendulum steady with respect to the movements of the frame, producing a graphic record of the duration and intensity of the Earth's movements. Separate instruments are needed to record the north-south horizontal, east-west horizontal, and vertical components of a tremor. By comparing the records produced by seismographs located in three or more locations across the Earth, the location and strength of an earthquake can be determined.
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