This is called Split Rudder and it provides redundancy. They run on different systems so if one fails, the other one can be used.
Here is a picture of a split rudder:
Split rudders also provide a finer high speed control, in that only the lower one moves at high speed, reducing the exposed surface area and therefore the control effect.
Very importantly, there is a structural benefit. When we use the rudder it imposes a twisting load on the vertical fin. By only using the lower rudder, when the aircraft is at high speed, we reduce the twisting moment and transfer that load to a bigger, stronger, part of the airframe. The principle is the same as why the outboard ailerons are disabled at high speed.
The patent information is here.