Why doesn't my door close properly after an earthquake?
It sounds as though there has been some movement of your house - particularly in this area. I'd recommend getting a surveyor in to assess the movement and see what else might need attention. This might be just the most obvious symptom of some more serious problems.

Assuming that it is just the door that's the problem then you need to "ease" the door by removing some of the wood from where it's sticking. By closing the door gently you should be able to see where it now hits the frame. You need to sand/plane/rasp this section of the door removing material until it fits.

If it's at the bottom you might need to take the door off its hinges to be able to do this.

Once you've got the door fitting properly re-seal the now bare edges to prevent moisture getting in that way.

You could remove some material from the frame, but that's more awkward.