So the decision to make a margin call is based on how far your asset has fallen against the amount of borrowed money to acquire it. In the case of the big boi's they are over-extended and if the markets do not rebound by tomorrow-mid-session- they all have some very larger decisions to make. This is also a slippery slope as when a margin call is made it is additional pressure (selling) and starts a feedback loop. They also know that by doing this it will make it worse for themselves as for every margin call made someone will be doing it to them-at that level.
Not trying to make a prediction about any of this. This a large part of the markets mechanical function and should be considered.
NOTABLE