You are absolutely right about the borders being a little distracting, they could have been narrower. They do however align with the lat/long grid.
The border seems a little out of place on small editorial maps like this. They call too much attention to the borders, which contain no content (such as lat/long spans, the original rationale for this type border).
Second, I wonder if you experimented with having the fault lines in white and the culture in black. That would have seemed more logical, to have the culture be part of the surface but the fault lines be "cracks" in it.
I did try the faults and roads reversed, but then there was too much emphasis on the roads and the faults receded.
Yes, they eded up being too thin, they are slightly more visible on the map, but they could have been better. They are actually everywhere on the map, you just can't tell
I'm having a difficult time identifying a "spreading ridge" on the map. Perhaps the double lines are hidden beneath an area dense with volcanoes/earthquakes?