Important Facts on Seismograph

A seismograph is a sensor that monitors and tracks ground tremors and motions, particularly during earthquakes. In most seismographs, a pendulum is mounted within a sturdy framework and coupled to a motorised, optical, or electromagnetic data acquisition system. Inertia maintains the pendulum stable with the motions of the frame when the Earth shakes or vibrates, resulting in a graphical recording of the severity and duration of the Earth’s motions. To measure the north-south horizontal, east-west horizontal, and vertical components of a tremor, separate devices are required. The position and intensity of an earthquake can be estimated by comparing the recordings collected by seismographs stationed in multiple locations throughout the world.

History of Seismograph

• In 132 AD, a Chinese man named Zhang Heng invented the first seismograph. It was created in the shape of a huge tin pot having eight vertical dragons pointing downwards. In the mouths of all the dragons was a single metal ball.
• The seismograph was known to release the ball from the mouth of the dragon, closest to the quake’s source, when the tin vibrated due to an earthquake. It was highly effective, and it even notified residents of an earthquake that had not yet occurred.
• In 1880, John Milne produced the first seismograph in the contemporary world. This seismograph used a long pendulum coupled to a stylus to detect earthquakes. The stylus was inscribed on carbon-coated paper when the ground shook. This resulted in a pattern that identified the quake’s direction and magnitude. However, one shortcoming in this design was that the oscillation was not dampened, causing computations to be influenced by accidental movements in the room. As a result, in 1898, a dampened swing was developed.
• Today’s seismographs design a coil that moves through a magnetic field when the Earth trembles. This movement generates an electric current, which is then sent into a machine.
• The introduction of an electromagnetic seismograph revolutionised earthquake monitoring in the twentieth century. In the 1960s, the World-Wide Standardized Seismograph Network was founded to track earthquakes in more than 60 nations. In addition, in 1984, the National Science Foundation established a national system to monitor and research earthquakes continuously.

How does a Seismograph work?

A seismograph is an instrument that utilises a ground-motion detecting sensor called a seismometer in conjunction with a recording system to measure the earth’s movement.

Consider a weight swinging on a spring as a primitive seismograph that is sensitive to up-and-down motions of the earth. The spring and weight are hung from a frame that travels with the ground’s surface. The vertical ground motion is measured by the relative velocity between the weight and the planet as it moves.

The relative motion between weight and the earth can be documented using a recording system, such as a revolving drum attached to the frame and a pen connected to the mass, to record ground motion called a seismogram.

Principle of Seismograph

The principle of the seismograph on which it works is the principle of inertia. The seismometer works on the inertia principle, which entails measuring the relative motion of the earth’s ground motion via a spring and mass held from a frame that travels with the earth’s ground surface. The motion between the earth and the mass produces an electrical voltage proportionate to the ground motion, recorded by the Digitizer as the earth moves. The seismometer is a force-balanced velocity sensor with feedback coils that send a current resisting any mass motion. The digitiser converts the analogue voltage from a seismometer into digital data.

Uses of a Seismograph

Scientists can use a modern seismograph to monitor earthquakes and analyse numerous characteristics of the event:

• The earthquake’s time of occurrence
• The epicentre, which is the location under the earth’s surface where the earthquake happens
• The depth at which the earthquake happened under the earth’s surface
• The magnitude of the earthquake’s energy release

Other Applications of Seismograph

• A seismograph captures ground oscillations induced by seismic waves that travel throughout Earth or along its surface from their place of origin.
• A volcano’s eruption is frequently accompanied by a series of minor earthquakes, mainly when the volcano commences activity after a lengthy period of dormancy. As a result, monitoring with sensitive seismographs is critical for anticipating volcanic activity.
• Small earthquakes frequently precede large earthquakes. The use of sensitive seismographs to detect minor tremors aids in the prediction of severe earthquakes.
• Microseisms, which are tiny and long-lasting ground oscillations that do not initiate earthquakes, are sometimes detected by seismographs. Storms at sea are linked to the occurrence of various microseisms.
• Seismographs are employed to detect nuclear weapons testing underground, where the relatively modest seismic waves produced by the explosion must be separated from natural earthquakes.

 Conclusion

A seismograph is a device that records seismic waves produced by earthquakes, explosions, and other Earth-shaking events. Electromagnetic sensors are used in seismographs to convert motions into electric currents, which are then analysed and registered by the instruments’ analogue or digital circuit. The phrases seismometer and seismograph are frequently used interchangeably; however, while both devices can identify and analyse seismic waves, only the seismograph can record them. A seismogram is a record created by a seismograph on a screen or as a paper printout.