(Bloomberg) -- The Federal Reserve’s hawkish signaling on Wednesday sent US stocks tumbling and drove a key index of volatility to the highest level since August, but markets are indicating that concern may be limited to the near-term. 

The Cboe Volatility Index spiked on Wednesday as the market’s so-called fear gauge reflected the souring in risk sentiment that followed the Federal Reserve’s decision. The index rose to 28 points on Wednesday from Tuesday’s close of about 16.  

The move of about 12 points in the VIX — which gauges expected 30-day volatility in the S&P 500 — dwarfed that in January VIX futures, which moved just 3 points. The gap between the two grew to the widest since the volatility shock in August, illustrating the impact of VIX’s focus on short-term options. 

The action in both situations was similar, with the spot index diverging from the front-month futures contract. 

That difference is interesting given the spot index is a calculation of expected forward-looking volatility based on S&P 500 options, whereas the futures showing relative calm are tradeable contracts often used by volatility-focused players. 

Some even shorter-term measures of volatility far outpaced the VIX move on Wednesday, underscoring the influence of ultra-short term options. The VIX 1-day and 9-day indexes rose 32 points and 22 points, respectively. The biggest growth in the options market has come from zero-day to expiry contracts, which now account for about half of S&P 500 options volume. 

Back in August, the relationship of the short-term spot index to futures reverted quickly, and that normalization appears to be happening again. Early Thursday, the VIX was back down to about 22.5, with the gap to January futures just over 2.5 points. 

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