Ground Motion  2
A Single Simple Wave
Think of a point on the ground vibrating to
and fro. If it kept moving the same distance each way,
it would have a constant amplitude of vibration.
If it moved 10 mm each way, its amplitude of vibration would
be 10 mm.
If the number of times it moved to and fro every second remained
the same, it would have a constant frequency of
vibration. Each to and from movement is called one
cycle of motion. If the patch of ground made 5 cycles
every second, its frequency of vibration would be 5
Hertz.
This graph shows how the position of the ground changes with
time as a wave with constant amplitude and frequency passes
through it. (Animate)
However, real ground
motion during earthquakes is not this simple.
