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The trace recorded by a seismometer is a record of how the ground moves during an
earthquake.
A single seismometer works in only one direction, and cannot give
a complete picture of wave motions from other directions. To overcome this problem, modern
seismograph stations use three separate instruments to record waves:
 | one to record the north-south waves; |
| another to record east-west waves; and |
| one to record the vertical waves. |
This combination of instruments tells a seismologist the general direction of the
seismic wave source, the magnitude at its source, and the character of the wave motion.
Instruments at other stations must be used to locate the earthquake's
epicenter.
The figure below shows a three-component seismogram.
Notes:
| the top component show the horizontal movement east-west; |
| the middle component shows the horizontal movement north-south; |
| the bottom component shows the vertical movement; and |
| the blue window identifies the P wave. |
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Seismometer traces with kind permission of:
Microseismology Research Group, University
of Liverpool |
Explore further...
The magnitude of an earthquake can be measured using the Richter scale. If you'd like
to find out a little more about the Richter scale, then click
here.
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