Observations on fault displacement D, fault length L, and surface-wave magnitude Ms, larger than 6, for 14 well-studied earthquakes in Iran are considered and the following relationships are established

  1. Ms = 1.259 + 1.244 log L

  2. Ms = 3.829 + 0.633 log LD

  3. Ms = 4.841 + 0.398 log LD2

  4. Ms = 6.575 + 0.999 log D

  5. log D = −3.832 + 0.914 log L

where L and D are in meters.

For 10 earthquakes, all the models pass the analysis of variance F test at the 95 per cent confidence level. In addition, the multiple correlation coefficients for equations (1) to (4) are above 0.90, and equation (2) has the highest value of 0.970. This value for equation (5) is only 0.747. Using these equations together with worldwide data, for the relation between Ms and log W, where W is the fault width, the following equation


is established between seismic moments, Mo and Ms. Moments obtained by this equation are in very good agreement with those obtained either from surface-wave and body-wave data or from field observations.

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