Screen Tearing occurs when your games reaches more Frames Per Second than your Display can Show (Hz)
So your fps crosses 60 and your Monitor Input is limited to 60Hz.
So Screen Tearing occurs.
This will help you Understand http://www.youtube.com/watch?v=o3p7YfrIxVc
How to Solve it?
Just go to Nvidia Panel and Apply Adaptive V-Sync.
Just Google how to Apply it.