A seismograph is a machine that feels the ground move and writes that movement down. When an earthquake shakes the earth, the machine makes a record — once a line on paper, now often a line on a screen — so people can see when the shaking started and how strong it was. You will hear the word in news after a quake and in science class. It is a technical word, but newspapers use it without fuss. Scientists sometimes keep a finer split: the sensor is a seismometer, and the seismograph is the whole recording setup. In everyday talk those two get mixed, and most speakers will call the whole thing a seismograph. It names the instrument, not the person who reads it, and not the science itself.

地震儀