A seismogram is a visual record that is created by a seismograph. A seismograph is a piece of equipment that records earthquake movements. These two items go hand in hand and are essential for the study of earthquakes.
Without a seismograph, there would be no seismogram. A seismograph detects movement in the Earth's crust, translating that movement through its inner workings to move a recording device, often a needle, that makes markings on what becomes the seismogram. The base of a mechanical seismograph moves beneath the hanging needle, and on the base rests paper. On the paper rests the needle, which should not move when the ground beneath it does. The resulting lines are a seismogram which can be read to understand information about the earthquake or movement, such as its intensity. Electronic seismographs produce printed seismograms. A seismograph can also be called a seismometer.
Seismographs and seismograms are also used to detect explosions, such as when a large bomb goes off, or volcanic activity. These items are used to detect not only how strong the vibrations are, but also to triangulate where the vibrations originate from. In other words, three seismographs in three different locations create seismograms that, when read correctly, can tell researchers where exactly the explosion or earthquake occurred.