Seismograph

Seismograph . It is a device used to record the amplitude of the oscillations of an earthquake ground or earthquake . Earthquakes can produce oscillations of the terrain vertically and horizontally, for this reason the oscillations in both directions must be recorded.

Summary

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• 1 The first seismographs
• 2 Function and utility
• 3 The sensors
• 5 Sources

The first seismographs

In its beginnings, it consisted of a pendulum that due to its mass remained motionless due to inertia, while everything around it moved; This pendulum had a punch that was writing on a time-ruled paper roll, so that when the vibration began, movement was recorded on the paper, this graphic representation constituting the so-called seismogram .

When an earthquake occurs , seismographs near the epicenter are able to record S and P waves, but on the other side of the Earth only P waves can be recorded.

Operation and utility

Horizontal seismograph.

It is used to record the horizontal movements of the earth during an earthquake. On a base fixed to the ground and through a rigid support a large mass is hung from a fine thread , this mass due to inertia practically does not move with the horizontal movement of the base and the flexibility of the thread, for this reason it remains static as the base moves to the rhythm of horizontal oscillations. Vertically the inelasticity of the thread keeps everything as a whole.

A very fine tip that works as an ink pen writes on the paper of a rotating drum a line equivalent to the relative movement of the base with respect to the pen or what is the same the amplitude of the oscillations of the ground.

The version of the seismograph for recording vertical movements is shown on the right. In this case the inert mass is fixed at the tip of a thin broad sheet , very flexible vertically but very rigid horizontally. In this way, the mass remains static due to the flexibility of the sheet in relation to vertical movement, but it faithfully follows the movements of the base in the horizontal direction, avoiding relative movement between the needle and the recording drum . As in the previous case, a fine pen traces on the paper of the rotating drum the amplitude of the vertical oscillations of the terrain.

The damper is necessary to prevent the flexible system from constantly oscillating at its natural frequency once its balance is disturbed . Professional seismographs are very sensitive devices that can also record horizontal oscillations in any direction and not in just one, as shown here.

Sensors

The sensors used in Earth’s seismometers are so-called geophones. In contrast, in the marine environment, in addition to the geophone, the hydrophone is also used to capture both land-based vibrations and acoustic waves that are transmitted by water .