In its earthquake mechanism studies the Dominion Observatory has been producing solutions graphically, but a program based on a probability function defined by Knopoff has been written for the IBM 1620 which permits the best solution to be obtained by a series of successive approximations from a given first approximation. The program prints out the strike and dip of the two nodal planes, their standard errors, the azimuth and plunge of their line of intersection, and a list of the stations producing inconsistent data. Weights can be assigned to each station; in practice these weights would depend on the past reliablity of the station.

The machine time required depends on the number of stations used, the accuracy of the first approximation and other factors; in general 20 to 30 minutes is required for a solution involving 30-40 stations.

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