In One Piece SBS someone asked Oda to tell from where Enel’s attacks originally come from:
D: Hello, Oda-sensei. I have serious suspicions, so forgive me if I pose a serious question. It’s about the names of Enel’s special attacks. It seems to me like many originate from the names of Scandinavian gods and Indian spirits. Can you please tell us what they all came from originally?
O: Yes. Well. The names came from a variety of sources. I can’t tell you a whole lot of in-depth information, but in general it’s pretty simple.