adder - 12:25 am on Jul 25, 2013 (gmt 0)
Well, then it's not to do with the EMD. If it was an EMD penalty, you'd rank #1 for The Widget Mountain.
Actually, some webmasters have reported similar activity on or around May 9th.
Have you been hit by any of the previous Panda updates?
It would be interesting to take a date range from Oct 2011 to this day and match it with the Google penalty timeline, just like you did on the graph you attached.
Moz has got one: [moz.com...]