// Program to convert Richter Scale numbers to energy.
//
// Both of these functions can take either a dimensionless number, which
// indicates a number on the Richter Scale, or a unit with dimensions of
// energy.  If a dimensionless number is passed in, this returns an energy.
// If an energy is passed in, this returns a dimensionless number which is
// the number on the Richter scale.
//
// The first approximation is due to Richter and Gutenberg, but this
// approximation uses a very narrow frequency band, which is not the band
// in which earthquakes primarily radiate their energy.

RichterGutenberg[n] :=
{
   if (n conforms 1)            // Passed in dimensionless.  (Richter number)
      return 10^(4.8 + 1.5n) J  // Convert to energy.

   if (n conforms joule)        // Passed in energy.  Convert to Richter.
      return -3.2 + 0.28953 ln[n/J]

   return "Error:  Expected dimensionless number or unit with dimensions of energy."
}


// The Choy-Boatwright approximation (1995) assumes higher-frequency components
// and is thus more realistic.  This returns the amount of energy radiated
// as seismic energy.
ChoyBoatwright[n] :=
{
   if (n conforms 1)             // Passed in dimensionless.  (Richter number)
      return 22387 e^(3.45388 n) J  // Convert to energy.

   if (n conforms joule)        // Passed in energy.  Convert to Richter.
      return -2.9 + 0.28953 ln[n/J]

   return "Error:  Expected dimensionless number or unit with dimensions of energy."
}