Huh. I've seen this exact blue/purple light in my hometown when I was a small kid (like 15 years ago). It was late night, we were in the patio with my family, eating nuts and talking, just a normal summer evening. We saw this light, and it deeply spooked us children. For years I was wondering what the hell was that. But since an earthquake didn't hit us that night (thanks god) I suppose it likely was something else.