How do seismographs record earthquakes?

A seismograph contains a sensor that responds to shaking from seismic waves. In a classic design, a suspended mass remains relatively stationary due to inertia while the instrument frame moves with the ground, creating a record of motion. Modern digital seismometers use electronic sensors and can detect very small vibrations from nearby traffic, explosions, and distant earthquakes. Networks of these instruments help scientists locate earthquake epicentres and study Earth’s interior. The first practical seismographs were developed in the late 19th century, and they remain essential to earthquake science today.