The nature of the sell off over the last 2 days seems to be related more to worries of the economic slowdown spreading to emerging markets. The biggest indicator of that is a sharp fall in Copper over the last 1 week. Although the S&P 500 is still above its August lows, Copper has sharply broken lower. China is the biggest consumer of Copper and there is a worry about the Chinese building boom slowing down. Yesterday Fedex talked about slowing down in Asia.
Following is a 3 month price chart for Copper.