How do seismographs record motion?

Seismographs record motion by using a suspended mass (or pendulum) that remains stationary while the ground moves during an earthquake. As the ground shakes, the base of the seismograph moves, causing the mass to stay in place due to inertia. This relative motion between the mass and the base is captured on a rotating drum or digital sensor, creating a seismogram that displays the intensity and duration of the seismic waves. The data can then be analyzed to determine the earthquake's characteristics.