Page 10 - Curriculum Visions Dynamic Book. To close the book, close the window or tab.

(Left) During the 1964 Alaskan earthquake these railway tracks were torn from their sleepers and refashioned into a wave.
(Below) Railway track before earthquake
and roll. The ground can pitch and roll for perhaps half a minute, although some earthquakes go on for much longer.
Earthquake magnitude and
intensity
It is possible to work out what the total energy released by the earthquake might have been, while it is difficult to find a single good measurement for an earthquake. The energy released is called the magnitude of the earthquake, measured by the richter scale. It is most useful for scientific investigations. But the magnitude does not describe the effect of the earthquake, and
for most people it is the intensity of the effect, not the overall amount of energy, which is crucial. The intensity, as expressed by the modified mercalli scale, is much more subjective and attempts to give a value to the effect of the earthquake.
The Richter Scale, named after Charles F. Richter
of the California Institute of Technology, is logarithmic, meaning that each one-unit increase on the scale represents a tenfold increase in the energy released by the earthquake. Thus an earthquake of magnitude 6 is 10 x 10 x 10, or 1000 times more energetic than an earthquake of magnitude 3. People cannot feel an earthquake smaller than magnitude 2.
(Below) To-and-fro motion can cause a railway line to break.
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(Below) The sideways movement of S waves can make the ground sway from side to side.
(Below) The effect of rolling surface waves can cause the tracks to buckle up.