The SVXY ETF is a "-1x" short exposure to the VIX, rebalanced daily. Very importantly, it is an ETF, and not an ETN. As an ETF, its holdings are fully transparent and posted on the fund sponsor's website, consisting of cash and two short positions on VIX Futures (one on the front month, another on F2) adjusted to 30-day duration. Again, very different from an ETN where the sponsor may take arbitrary hedging positions "behind the scenes" to limit their tail event exposure.
How did such a simplistic structure survive the 115% VIX move of February 5th, 2018 without going insolvent? The ETF NAV should have gone to $0 or below, but instead it "only" lost 80%+ of its value.
Asking on the quant exchange on the assumption that there's some serious financial engineering involved.