The purpose of this paper is to determine from the seismograms of a tectonic earthquake the line of the motion which generated the observed S waves (tectonically, the A axis). By noting certain geometrical relationships between the faulting motion and the emitted S waves, it is possible to derive a method which determines the line of the generating motion from observations of the generated S waves. The results of the application of the proposed method of S wave analysis should, theoretically, make it possible to determine which of the two solutions given by the P wave method of analyzing the tectonic mechanism of earthquakes is the correct solution. The proposed procedure is applied to data collected from the original seismograms of four earthquakes as recorded at seismic observatories throughout the world. There is such poor agreement between the S wave results and the previous P wave solutions that it is necessary to conclude that one or more of the following is true: either the mechanism assumed is not the type actually occurring; the phase identified as the S wave does not correspond to the first P wave motion; the P wave method is incorrect or inadequate; or the S wave method is incorrect or inadequate. To select among the various possibilities necessitates a discussion of the relative merits, defects, and potentialities of the two methods.

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