Adam Warner toma esta pregunta (referenciada principalmente a un posible objetivo del Gobierno Estadounidense) y la responde elegantemente en un post.
Want to know how you can “manipulate” the VIX?
You would have to do something radical like … buy some near-term puts on the S&P 500 (SPX). Yes, believe it or not, that’s basically all the VIX measures. It’s an index of volatility on SPX options normalized to 30 days duration.
The government, or an average-size hedge fund, could spend a few million dollars and pay up for some puts. It would lift implied volatility across the board for a short time, with the chance of the elevated volatility persisting if it caused a chain reaction.
Which brings up another point: It’s overwhelmingly likely that VIX broke above 30 thanks to a weak market. So what did the VIX tell you that you couldn’t infer anyway? The answer in this narrow case is nothing.
So, to answer the original question, there are a lot of things to worry about out there. The government buying or selling some SPX puts to influence a volatility index is hardly one of them.