What is the energy of an earthquake?

Earthquakes release energy in several forms:

  • The energy in seismic waves that cause the ground to shake
  • Heat energy associated with friction on the fault slip surface
  • Gravitational potential energy (the energy stored when lifting something off the ground, for example) may change as a result of the earthquake
  • Elastic potential energy, as in the recoil energy of a stretched spring

We can directly measure the first of these energies, that in seismic waves. The other types of energy cannot be measured directly, but can only be indirectly inferred.

Charles Richter was one of the first scientists to propose an equation to compute the seismic wave energy from earthquakes. We can use his approach to compute the numbers in the following table, where we use Megatons of TNT as the unit of energy. The atomic bomb dropped on Hiroshima in 1945 released the equivalent of 16 Kilotons = 0.016 Megatons of TNT, about the energy equivalent of a magnitude 6 earthquake. The largest hydrogen bomb ever detonated was the Tsar bomba device exploded by the Soviet Union on October 30, 1961, with an energy equivalent of about 50 Megatons of TNT.

Earthquake Magnitude Energy Equivalent in Megatons of TNT
3 0.0000005
4 0.000015
5 0.0005
6 0.015
7 0.5
8 15.0
9 500.0
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