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.

d = Asin(2ft)

  d = displacement in mm
  A = amplitude ( here, 10mm)
  f = frequency (here, 5Hz )
  t = time in seconds


 page 2 of 3

Vibrating Buildings
       Ground Motion - 2

from Bristol University