Volatility interruption (VI) triggers for individual stocks and exchange-traded products have moved in lockstep through this year's market swings, but the two have split sharply since Korea opened an afterhours trading session. Individual stocks, now trading over longer hours with thin liquidity, have seen halts return in force, while exchange-traded products — excluded from afterhours trading and hit by tighter rules on single-stock leveraged funds — have seen triggers plunge.
VI triggers for individual stocks totaled 13,236 last month, up 33.8% from 9,890 in August, according to the Korea Exchange on the 6th. Triggers for ETFs and ETNs fell 67.1% over the same period, to 533 from 1,622, the lowest monthly figure this year. A VI switches a stock to single-price auction trading for two minutes when its price moves sharply outside a set range, curbing abrupt swings.
The two series tracked each other closely earlier this year, rising and falling with overall market volatility. July brought an especially violent swing, with sidecars and circuit breakers firing repeatedly, and individual-stock VI triggers peaked for the year at 21,131. As index swings eased, individual-stock triggers more than halved in August, while ETF and ETN triggers fell 68.9% over the same period.
The two paths began to diverge when the afterhours market opened in mid-September. The exchange extended trading hours on the 14th of last month, allowing real-time stock trading from 4 p.m. to 8 p.m. after the regular session closes. That added a window in which individual stocks could trigger halts after the close, pushing the count back up.
Because the afterhours session applies the same VI thresholds as the regular session despite thinner liquidity, the alarms sounded far more often. On the first day, the afterhours session alone saw 1,112 VI triggers, about 2.8 times the 391 recorded in that day's regular session. The count fell quickly afterward but still reached 553 on the 18th of the same month, above this year's daily average of 494 for the regular session. Given that afterhours volume in the opening week was only about 6% of regular-session volume, the safeguard intervened far more often than the trading activity would suggest.
Cases in which dynamic VI, which catches sudden price moves, and static VI, which controls cumulative price changes, both reached their thresholds at the same time jumped more than thirteenfold, to 3,009 in September from 225 in August. Of those, 97.5%, or 2,933, came after the afterhours market opened. Total daily VI triggers also more than doubled, averaging 890 over the following 11 trading days from 431 over the eight trading days before the launch.
Exchange-traded products, by contrast, were left out of afterhours trading just as enthusiasm cooled for the single-stock leveraged funds that had driven market activity, sending their VI triggers lower in short order. Triggers for single-stock leveraged and inverse products based on Samsung Electronics and SK hynix fell 93.5% in two months, to 55 in September from 312 in August and 843 in July. The drop is attributed to higher barriers to entry, after minimum deposit requirements were raised in late July and mock trading was made mandatory in August.
The exchange has tightened market oversight since extending trading hours. Its Market Oversight Commission has set up a special surveillance task force of nine staff — three each for monitoring, prevention and short selling — to operate through year-end, linking regular-session and afterhours trading records to screen for abnormal activity. An official in the financial investment industry said the market is still working through an early phase in which liquidity is insufficient, filtering out sharp price moves and searching for fair prices, and added that as more participants join and order books thicken, the tendency for prices to move sharply on small trades could ease.
