A three-dimensional modelling tool has been constructed to facilitate the study of P-wave nodal solutions. This model consists of two basic interrelating parts: a fixed hemispherical basin that represents the lower half of the focal sphere and a cursor consisting of three orthogonal components, one plane representing the fault, another representing the auxiliary plane, and a third containing the (deviatoric) stress vectors. This model displays clearly all the important parameters associated with P-wave nodal solutions, in contrast to conventional (e.g., equal-area) two-dimensional projections that have inherent limitations. In addition this model is useful as a pedagogical tool; this model can also be used as a check on theoretical calculations, which, depending on the technique used, may be nonunique, for the case where surface-wave data are incorporated with body-wave data to place more stringent restrictions on fault plane solutions.

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