The authors hypothesis postulates that the Baja California microplate is transported along the North America-Pacic plate boundary by partial coupling to the Pacic plate and low coupling to the North America plate. To test this idea, they use numerical modeling to examine the interplate coupling on a multiple-earthquake-cycle time scale along the Baja California-Pacic plate boundary and compare the modeled velocity eld with the observed geodetic motion of the Baja California microplate.