1. Seismometers: These sensitive instruments detect tiny movements in the ground and convert them into electrical signals. Three or more seismometers work together to sense vertical and horizontal movements. Seismometers have pipes for cables, solar panel providing electrical energy to charge the battery which powers seismometers and computer. Seismometers are placed on the bedrock and the base is cemented to the bedrock. The computer is also placed on the cement base.
2. Computer: A computer receives the signals from the seismometers and stores the data digitally.
3. Seismogram: Digital data are sent to a survey office, where they are turned into a seismogram. The example below shows a Mw 5 aftershock of the Northridge, California, earthquake. The time interval between the P and S waves indicates how far the seismometer was from the quake center.

Seismogram displays ground displacement (usually in millimeters) along with the P and S waves and time scale.