On the Sub-Rotation of a Plate

Marco Cuffaro, M. Caputo, and C. Doglioni

During their absolute motion over the Earth's surface about their poles of rotation, some plates may experience a further sub-rotation around a second sub-pole. In this case, the instantaneous pole of rotation can be a third separate pole, being the combination of the two basic poles, i.e., the absolute motion-related first pole, and the sub-rotation pole. The sub-rotation pole is the only point of the plate that does not change distance relative to the absolute pole. An analytical method can separate the sub-rotation from the absolute plate motion when sufficient space geodesy data are available.

We applied this model to North America, which is moving WNW-ward in an absolute reference frame, with the first pole located at -64.30°N and 105.52°E; the plate contemporaneously sub-rotates counter-clockwise about an internal pole located at 50.78°N and -77.78°E. The combination of the two poles generates a third migrating instantaneous apparent pole of rotation, that is located at -1.55°N and -82.59°E, which does not comprehensively describe alone the composite motion of the plate.