What we saw earlier was the bitfinex algorythm in case of margin call cascade.
This is the explanatation of how it work (not official one, just guess).
There is a limit for the margin call cascade of about 10% drop in 1 minute. Then the algo stop market selling the bitcoin, and let the buy order to fill the gap. Then it sell again to the previous limit and repeat the processus until it sold every bitcoin from the margin calls.
I m open to any suggestion or comments
Edit : the begin of the action was due to a single 5k sell order to 575.