seis·mo·graph (sīz'mə-grāf') n. An instrument for automatically detecting and recording the intensity, direction, and duration of a movement of the ground, especially of an earthquake. seis·mog'ra·pher (sīz-mŏg'rə-fər) n., seis'mo·graph'ic (-grāf'ĭk), seis'mo·graph'i·cal (-ĭ-kəl) adj., seis·mog'ra·phy n.