Computer-determined P nodal solutions in the Wickens-Hodgson Catalogue were compared with earlier visually-determined solutions for the same earthquakes. Good agreement was found in about 40 per cent of the solutions. Lack of agreement was due chiefly to poor distribution of data in azimuth about the epicenter. Necessary, but not sufficient, conditions for well-defined nodal plane solutions were determined: there must be a minimum of 100 observations with at least two in each 90° segment of azimuth; data must be at least 80 per cent consistent with the selected nodal planes. Fourteen of the 618 earthquakes in the Catalogue met these requirements.

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