Seismographs are the primary tools of seismologists. A basic seismograph has a heavy mass suspended from a frame. When the Earth shakes, the frame moves, but the heavy mass stays still. A pen attached to the mass records the relative movement on a rotating drum or digital medium. Modern “seismometers” use electronic sensors to detect even tiny tremors invisible to humans. By analyzing the seismogram, scientists can calculate the distance to the earthquake, its magnitude on the Richter scale and even the type of fault movement that occurred, providing critical data for both research and early warning systems.