From August 1 through August 10, when the Standard & Poor’s 500 Index plunged 13.3 percent amid surging volatility, high-frequency firms tripled their volume and may have accounted for 75 percent of U.S. shares changing hands.

Whenever the stock market plunges for several days it reminds us the stock market crash in October 1929, which triggered the 12-year great depression that hit all the western industrialized nations. It all began on a “Black Thursday“, Oct. 24, 1929, when share prices on the New York Stock Exchange (NYSE) collapsed. Stock prices plummeted on that day, and continued to fall at an unprecedented rate for a full month.

Is the August 4th, 2011 stock market signaling the kind of “Panic Selling” that contrarians look for in forecasting the end of a decline or has a August 2011 “Bear Market” just started?

Shares of online radio firm Pandora Media Inc. plummeted on their second day of trading as the Pandora IPO date departed and investors suddenly fled for the exits. BTIG analyst Richard Greenfield this afternoon launched coverage of Pandora Media with a Sell rating and a $5.50 price target.

The Dow Jones Industrial Average is currently off 7% from its April high and has broken decisively down through its 50 Day Moving Average — the Federal Reserve and economist have also described this current down trend as a “Soft Patch” but the markets are not so sure.