[oelmekki]

Yes, this USDTUSD market on kraken is an anomaly: it has very small volume, and nobody is really interested in trading that.

Poloniex has many USDT markets, as they use it to compensate for the fact they do not provide markets against fiat. As such, those markets have way more volume.

The market visualization and analysis tools website tradingview.com offers a computed charts of USDTUSD from poloniex (symbol: POLONIEX:USDTUSD). It tells a whole different story than kraken charts: https://www.tradingview.com/chart/?symbol=POLONIEX:USDTUSD . Basically, usdt is stable there.

There's still a problem here: tradingview does not tell (afaik) how they are computing this price. I would assume they do a mean or average of various BTCUSD markets on several exchanges, then check it against BTCUSDT on poloniex, or something like that. But I don't know any official explainer about it.