Note, I truly have no idea what it is caused by though.
I'm no expert but I believe screen tearing is caused by your FPS - frame-rates per second - being faster than the speed that your monitor can refresh itself. Supposedly, it's dependent on your monitor being able to keep up with a faster FPS. With a low FPS, your monitor probably will not tear but your game will look a little choppy. I think most new monitors only go to about a max of 60FPS, so if your FPS is faster than that you might find some tearing. However, and I'm not sure about this, some of the newer monitors may be able to refresh images at faster rates.
To avoid this problem, it's best to enable VSync options, which caps your FPS to however fast your monitor's refresh rate can allow. That said, I don't know if consoles can enable options like that but it may be that the 360 has built in VSync to allow minimal screen tearing. I've only encountered screen tearing on newish - for consoles - open world games like Fallout 3, and even then it wasn't that bad. Only like a few instances or once in a while.
I don't know, that's about all I know. :shrug: