Geologists peer into the Earth using a seismometer, an instrument that senses ground movements from earthquakes. A weight is attached to a pendulum or stiff spring, and when the seismic waves cause ground motion, the weight remains stationary while the rest of the instrument moves with the ground. A rotating drum, or seismograph, graphically records the movement over time.
Topic: Earth Science
Keywords: Earthquake magnitude, Earthquakes, Scientific apparatus and instruments, Seismometers