DAN MCKENZIE AND ROBERT PARKER'S 1968 GREAT FIGURE CONFIRMING PLATE TECTONCS

Good figures perspicuously display what is being represented. The figure (Figure 3) that Robert Parker provided Dan McKenzie (McKenzie and Parker, 1967) of the movement of the Pacific plate relative to a bordering plate containing North America, and much of Asia wonderfully displayed McKenzie’s use of slip vectors to confirm plate tectonics. Once McKenzie began thinking about Euler poles as instantaneous, he hit on the idea of using slip motions of earthquakes. He also realized that he did not have to restrict himself to pure strike-slip earthquakes but could obtain slip directions from looking at the horizontal slippage of slip-dip earthquakes. This led him to earthquakes along the common boundary of the North American and Pacific plates. Once McKenzie found that great circles perpendicular to the slip vectors of a few earthquakes intersected Earth’s surface at two points 180^o apart, he knew he was on the right track. He then ask Parker, his officemate at Scripps, and fellow graduate from the Department of Geodesy and Geophysics at Cambridge, if he had any good ideas about how to display his findings. Parker had the perfect answer, an oblique Mercator projection that showed McKenzie’s confirmation of plate tectonics, by perspicuously showing that all slip vectors were roughly parallel with each other and with the upper and lower boundaries of the figure.