According to [1] (2018) , actually getting down to the metal to track what happens in the tether blockchain isn't straightforward.
According to coincap [2] there is around 20B tether in circulation.
Also according to coincap, the Bitcoin market cap is around 380B.
Now, the question is one of market depth: can 20B be used to manipulate a 380B market.
What I would very much like to see is an aggregate market depth number for - say - the top 30 exchanges. Does anyone have a reference for this?
[1] https://hackernoon.com/a-closer-look-at-tethers-blockchain-5...