A formal method of analysis is proposed whereby groups of first motion solutions may be examined for evidence of regional patterns of symmetry, abstracting from any particular model of the focus or from assumptions about regional tectonics. Axial, planar, and conical symmetry are discussed with special consideration being given to the constraints placed on the spacial distribution of axes by the geometry of sets of orthogonal axes. Examples from the literature are given of axial and planar symmetry, and it is shown that in some instances attention to the geometry of the axis system suggests modifications in the interpretation of regional patterns. Analytical aids are also given to associate the use of eigenvalues with the graphical methods in discerning the type of symmetry and indicating the degree of scatter, and a method is described for calculating statistical confidence limits for the case of axial symmetry.

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