The primary use of a seismograph is to detect and record the vibrations caused by seismic waves during an earthquake. A seismograph consists of a mass attached to a fixed base. When seismic waves travel through the Earth, the base moves while the mass remains stationary, creating a trace on a recording medium. This trace allows seismologists to analyze the characteristics of the earthquake, such as its magnitude, depth, and epicenter. The data gathered from seismographs is crucial for understanding seismic activity, informing building codes in vulnerable areas, and providing early warning systems.