Ha... one day I was flying over Turkish mountains, and found a similar pattern. I was thinking that they really messed up the scenery, with obvious lines going through the mountain ranges when you look at them from LVL340.
Then I realised that I was flying for real (pax on a real jet)!
Some times reality also has patterns like that.
Now, the 2 cents of my opinion on your problem... Looks like a default scenery which has a texture map that repeats. Usually you can create texture maps that don't repeat (no matter how far you go, you still can not see the edges of the texture rectangle). This looks like a bad job...
Agree with Eric, perhaps a better default scenery will take care f it.
Have fun,
Alex