Search:

Present

Что здесь происходит? What is going on here?
Иногда это случается. Sometimes it happens.

(Oh, I was wrong! There is the difference: случаться may not be continuous, only repeatative,...

I don't see any difference between these two pairs of verbs in sense of "to happen" - they are completely interchangeable IMHO.

I have added some new info to my previous post.

to happen

Imperfective / Perfective

Infinitive

происходИть, случАться
/
произойтИ, случИться

Looks like difference between perfective and imperfective verbs is the biggest problem when learning Russian.

Here is the link to the latest discussion about that....