Interpretation
The properties of triple junctions are most easily understood from the purely kinematic point of view where the plates are rigid and moving over the surface of the Earth. No knowledge of the Earth's interior or the geological details of the crust are then needed. Another useful simplification is that the kinematics of triple junctions on a flat Earth are essentially the same as those on the surface of a sphere: despite describing plate motions as involving relative rotations about poles and plate motions on a flat surface being defined by vectors. The relative motions at the triple junction are the same.
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