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Energy Calculator

The occurrence of an earthquake is a complex energy conversion process. When an earthquake occurs,
much of the available local energy is used to power the earthquake fracture growth, producing heat rather than
generating seismic waves which radiate outward and are detected by seismographs.

The seismic moment is a measure of the total amount of energy that is transformed during an earthquake.

Usually only 1-10 percent or less
of an earthquake's total energy is released in the form of radiated seismic waves.

How much energy is converted / released in an earthquake?

(1) Enter the published Earthquake Magnitude value into the table
(2) Click "Compute" or press Return/Enter on keyboard 
(3) Compare energy levels in various equivalent measures 
Earthquake Magnitude  Enter Value 
 Seismic Energy in Waves Radiated from Earthquake Source:   Joules
Total "Seismic Moment Energy" (MO):   Joules

Calculated Seismic Energy
Approximated in Everyday Equivalent Measures

Seismic Moment Radiated Energy
Power the USA for:   Days
Power New York City for:   Months
Equal the Hoover Dam Electricity output for  Months
 Equal the Energy of an Average Hurricane for:   Seconds
Power the Average USA Household for  Years
Equal the Energy in:   Hiroshima Atomic Bombs
Equal the Energy in:   Average Lightning Flashes 
Equal the Energy in:   Tons of TNT
Equal the Energy in:   Gallons of Gasoline
Equal the Energy in:   Sticks of Dynamite


Richter Scale vs Moment Magnitude Scale

Since the late 1930s it became commonplace to measure earthquakes by their magnitude, given the work done
by Gutenberg and Richter, and the publication of the logarithmic Richter Scale which related to a measure of the 
energy radiated by the earthquake, using well-calibrated seismic stations.  At the time, the general properties of
the radiated spectrum were not known and the concept of seismic moment and the moment tensor 
had not yet been developed.

The Richter scale only describes the maximum wave amplitude, and does not give any indication of the total energy
that is released by the event.  
The moment magnitude scale measures the total energy released by an earthquake.
It now supersedes the Richter magnitude scale which measures the height of a seismic wave.  The two scales will 
indicate similar results if the earthquake magnitudes are between 3.0 and 7.0.

Seismologists studying larger earthquakes (greater than M3.5 - M4.0) generally report the size of the earthquake
using the moment magnitude scale.  For smaller earthquakes, the published magnitude is usually given as MB
MS, or ML.  
The concept of moment magnitude (MW) was introduced in 1979 by Hanks and Kanamori and has 
since become the most commonly used method of describing the size of an event.  Moment magnitude measures
the size of events in terms of how much total energy is released.  

More Information about Earthquake Magnitude and Seismic Moment

Specifically, moment magnitude relates to the amount of movement by rock; i.e. the distance of movement 
along a fault or fracture and the area of the fault or fracture surface.
 It is calculated as 

MO = µAD

where µ is the shear modulus of the rocks included in the fault (dyne/cm2)
A  is the area of the fault rupture in cm2
and D is the average fault displacement in cm

Thus, MO is shown in units of energy, dyne-cm

Both the earthquake magnitude and the seismic moment are related to the amount of energy that is radiated by an
earthquake.  Richter, working with Dr. Beno Gutenberg, developed a relationship between magnitude and energy.
That relationship is:

logES = 11.8 + 1.5M

giving the energy ES in ergs from the magnitude M. 

Note that ES is not the total "intrinsic'' energy of the earthquake, transferred from sources such as gravitational energy
or to sinks such as heat energy.  It is only the amount radiated from the earthquake as seismic waves, which, as was 
said above, is in most cases only a small fraction of the total energy transferred during the earthquake process. 

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