The hanging wall is less constrained, so moves more in the earthquake. It depends also on how shallow the rupture extends. If the rupture does not extend all the way up to the ocean floor, it would be more symmetric. There is some debate whether slip tapers, even in the biggest events, toward the surface, and accretionary prisms are complicated to interpret. Intuitively, I think this applies more to the horizontal motion, the vertical is partly determined by the flexing of the subducting plate, and so it more complicated.

I see I wrote lots of waffle words, this is not my specialty, and of course no map of deformation is available yet for this event.