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[SEAOC] Re: [SEAOC] Help: Calculate Ms from Ml or Io ...

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Surface Wave Magnitude

Ms = log A + 1.66 log (Delta) + 2.0

where:  A      = max. ground displacement in micrometers
           Delta = epicentral distance of the seismometer measured in degrees
(360                        degrees correspondeng to the circumference of the

Local Magnitude is defined as the log of the maximum trace amplitude  ( in
micrometers) recorded on a Wood-Anderson seismometer located 100 km from the

See "Geotechnical Earthquake Engineering", Steven L. Kramer, Prentice Hall,
1996, pp 48-49.