I saw this sentence on a Japanese teaching site:
The incident occurred last week
Japanese Language Stack Exchange is a question and answer site for students, teachers, and linguists wanting to discuss the finer points of the Japanese language. It only takes a minute to sign up.Sign up to join this community
As a native speaker, I also feel uncomfortable with 事故は先週に起こった, which can be said to be a little unnatural but probably cannot be said to be ungrammatical. 先週 plays the role of an adverb in this sentence, so its natural sentence will be:
But as a writer, I would like to avoid this, because I don't like the awkward sequence of Chinese characters of 先週 + 起. So I like this sentence transcribed like this with the use of punctuation marks.
This point might be trivial for other Japanese, but I am always wondering how to use this kind of noun phrase used as an adverb. In order to avoid this (discomfort), I prefer the following to the above sentence.
After answering this question, I hit upon the following sentence.
This sentence with に in it is, no doubt, grammatical and quite natural. I have no idea of the cause of the difference in naturalness and grammaticality between this and the above sentence (事故は先週に起こった).