How Can Adjacent Parts of an Oceanic Plate be Subducted in Different Directions?
Where one part of a plate continues almost horizontally while an adjacent section is driven down into the mantle, wouldn't that cause a violent fracture of the plate, and if not, why not? 


In case of the Nazca plate probably not because that is still warm and partly ductile (see the linked work in the other thread). Also, these cracks and deformations happen as the plate subducts, they don't displace a huge pile of material in one single event, like does a movement along a transform crack (e.g. San Andreas), or a "megathrust" earthquake along a subduction zone. A whole plate breaking along the bend line otoh can trigger catastrophic earthquakes.

I could not find a specific work that deals with the interface between a steep and a shallow subduction, but a work discussing the dynamics of the Nazca plate subduction. They state that the ridges (being warm and buoyant) are subducted because of the movement of the adjacent slabs (dragged along so to say), and becaue of global plate motion, meaning the earth can't change volume so some parts just must give way for emerging parts elsewhere (Atlantic opening is mentioned). There is a map of epicenters of (generally low mag) earthquakes (and links to other work) along the Nazca subduction as well as above the flat segments, suggesting that the cause there is the greater friction. The oceanic crust, being quite topographic, is flattened while being pushed or drawn under the continent.

Earthquakes because of segmenting as asked in the OP aren't mentioned specifically.

I find it interesting, maybe someone else knows more.