GARY HINCKS / SCIENCE PHOTO LIBRARY GARY HINCKS / SCIENCE PHOTO LIBRARY
Seismograph. Artwork of a seismograph or seismometer machine for recording ground movements caused by seismic activity, such as earthquakes. The device consists of a heavy pendulum inside a casing that is fixed to the ground. A pen is suspended beneath the pendulum, in contact with a paper drum. When an earthquake or tremor occurs, the pendulum and pen remain stationary, but the paper drum and casing move with the ground. A record of the movement is thus recorded on the paper drum. This trace is known as a seismogram and is used to measure the intensity of an earthquake. Seismographs may also be of use in predicting the occurrence of volcanic eruptions.
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