A study of over 1500 P-wave phases which pass, for the most part, through the upper mantle beneath Western Canada, shows that there is no significant lateral variation in P-wave velocity structure beneath Western Canada, and that the Wiggins and Helmberger model for the Western regions of the United States does not fit the data for Western Canada.One possible interpretation of the data for Western Canada is closer to the classical Herrin model of P-wave velocity as a function of depth than it is to the Wiggins and Helmberger A model.

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