Board Thread:Skyrim/@comment-108.220.171.72-20150715165317/@comment-6881629-20150715175014

Maybe they were already in the base game and the dlc just added the quest (that was mentioned in the other thread i linked above). Some people also say inside tombs and around Dwemer ruins can have small quakes. It could very well just be for a bit of extra immersion in the world.

There are also some traps (like Bandit Bridge) that can cause the screen to shake, they can be set off by npcs or creatures so can sometimes trigger before you get that close to them (or even in sight of them).