Home Science Who Measures Earthquake Motions ? Seismo What ?

Who Measures Earthquake Motions ? Seismo What ?


It’s Called Seismometer !

Seismometer or seismograph is an instrument that measures motions of the ground, including those generated by earthquakes, nuclear explosions, and other sources.


Records of seismic waves called seismograms allow to map the interior of the Earth, and locate and measure the size of those different sources.

It is often used to mean seismometer, though it is more applicable to the older instruments in which the measuring and recording of ground motion were combined than to modern systems, in which these functions are separated. Both types provide a continuous record of ground motion; this distinguishes them from seismoscopes, which merely indicate that motion has occurred, perhaps with some simple measure of how large it was.


Image source: Google Image

Seismographs are securely mounted to the surface of the Earth, so when the ground starts shaking, the instrument’s case moves.

What doesn’t move, however, is a suspended mass inside the seismograph, called the seismometer. During an earthquake, the seismometer remains still while the case around it moves with the ground shaking.

Image source: Google Image

Because seismographs can only measure movement in one direction, many seismograph stations have multiple seismographs to record the north-south, east-west, and vertical motions of the ground.

A simple seismometer that is sensitive to up-down motions of the earth can be understood by visualizing a weight hanging on a spring. The spring and weight are suspended from a frame that moves along with the earthʼs surface. As the earth moves, the relative motion between the weight and the earth provides a measure of the vertical ground motion. If a recording system is installed, such as a rotating drum attached to the frame, and a pen attached to the mass, this relative motion between the weight and earth can be recorded to produce a history of ground motion, called a seismogram.

Any movement of the ground moves the frame. The mass tends not to move because of its inertia, and by measuring the movement between the frame and the mass, the motion of the ground can be determined.

IN ANCIENT ERA, Zang Heng of China’s Han dynasty , invented the first seismoscope. “Instrument for measuring the seasonal winds and the movements of the Earth”.


It contains a large bronze vessel, about 2 meters in diameter; at eight points around the top were DRAGON’s heads holding bronze balls. When there was an earthquake, one of the mouths would open and drop its ball into a bronze TOAD at the base, making a sound and supposedly showing the direction of the earthquake.


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