What is the reason for this severe price drop over 2011 for Fig Tree Pocket ?

Fig Tree Pocket and Brisbane's western suburbs generally hold prices well. Fig Tree Pocket is home to some of the most affluent river front properties in Brisbane due to it's secluded yet convenient location. Obviously this question is about prices in 2011. Flooding in January 2011 did affect property prices in Fig Tree Pocket and much of Brisbane riverfront was affected however Fig Tree Pocket and the Brisbane Riverfront in general is bouncing back. It's a great time to buy in Fig Tree Pocket with plenty of upside.

Floods - and fig tree pocket is being built out with big houses, which means the nice bush is disappearing.

I am not sure about Fig Tree Pocket itself, however, that western part of Brisbane was the hardest hit by the floods last year. I would say that this is the biggest factor here. What others have said above is also true - Fig Tree Pocket is known as one of the "big house, big budget" areas, so it would not be completely unlikely that maybe some have been hit hard by the GFC and are in a position where they have to sell.

2011 found realistic vendors in the area? Much of Brisbane was overvalued since middle of last decade so a correction was needed at some point. The GFC & floods did not help of course.

The credit crunch in 2008 started the slump in house prices as the banks started tightening the requirements of lending because of the unstable economy.
Some houses had been over valued by the banks velures when sellers had purchased the house and that gave the seller the idea the house was worth more than it really was worth in today’s market. This is wide spared world wide.
On top of the credit crunch the 2011 flood did not help. The floods in Qld saw the house prices drop again with the banks going out and revaluing houses that were hit by the flood or houses that were in flooded areas but not flooded. People were scared off even more with the floods.

Qld is hit harder than any other state for house prices because of the floods but the drop in house prices are state and worldwide. It will take some years before the economy will pick up and house prices stabilise.