Hawaiian Volcano Observatory


Mauna Loa


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Volcanic Hazards

Procedure for calculating local magnitude, ML

from Earthquakes by Bruce A. Bolt (W.H. Freeman and Company, 1988).

  1. Measure the distance to the focus using the time interval between the S and the P waves (here S-P = 24 seconds).
  2. Measure the height of the maximum wave motion on the seismogram (23 millimeters).
  3. Place a straight edge between the appropriate points on the distance (left) and amplitude (right scales to obtain magnitude ML = 5.0.

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