In a number of shuls that I have attended, I have noticed that the congregation stands for certain sections of Torah readings. Specifically:
- Aseret Hadvarim - The 10 Commandments
- Az Yashir (song at the sea)
- Parshat Zachor (when read only on parshat Zachor)
- The last verse of each book of the Torah prior to saying "Chazak..."
- When a Bar Mitzvah boy reads maftir
I see that we do have a question related to the 10 commandments, so you don't need to address this. Is there any source or precedent for standing in any of the other occasions that I mentioned? Or is just a specific shul minhag?