What instrument records the ground motion produced by earthquakes?

A seismograph records the ground motion produced by earthquakes.

A seismometer is the sensing instrument, while “seismograph” traditionally refers to a seismometer together with the system that records its measurements. Modern instruments often record digital data, but the familiar concept is a relatively stable mass and a frame that moves with the ground.

The difference between the mass and the surrounding ground reveals motion. Older instruments drew waveforms on paper; modern networks transmit digital recordings to monitoring centers. The resulting record is called a seismogram.

Seismographs help scientists determine an earthquake’s timing, location, depth, magnitude, and wave types. They also monitor volcanic activity, underground explosions, and slow ground motion. A seismograph does not itself “feel” an earthquake in the everyday sense; it measures specific physical movement, including motions too small for people to notice.