Juuuuuuust kidding, game runs at 60fps now, but the tearing has now returned in a new form, now being a diagonal strip from the top left. neato

Using the force openGL command solved everything, thank you very much!

Please post a log file (factorio-current.log). You can find it here:
%appdata%\Factorio (usually C:\Users\<username>\AppData\Roaming\Factorio)

It could be an Nvidia driver issue as several users have reported this problem (https://forums.factorio.com/21308, https://forums.factorio.com/21780 ...

Odd bug that has shown up recently for me. I played through the campaign with no issues graphically, but as soon as I moved to single player my screen started tearing so badly I couldn't play. Yes, I turned vsync on in game, and yes I turned vsync on in the nvidia control panel, and neither of them ...