Here is a nice animation of the exaggerated motions of a big rupture on the Hayward. You have to look at both frames in order to understand it. The rupture starts at the northern tip and proceeds south. You can see the P-wave running ahead of the S-wave. The rupture looks like it is zooming at the S-wave velocity, so it is not a 'super rupture'. (maybe, maybe not)
However, during the rupture, the P-wave maintains a steady distance, until the end of the fault, then increases its gap in the free-field. As well, there is a slight kink in the P-wave spread. So most likely, the model fully incorporates the concept of pre-rupture displacement, as well as a critical displacement. So there are some elements of a high speed rupture.
I've looked at it enough. Tell me if you see any directivity.