A new study says “flash crash” events happen routinely, at speeds so fast they don’t register on regular market records, with potentially troubling consequences for market stability.

The analysis involved five years of stock market trading data gathered between 2006 and 2011 and sorted in fine-grained, millisecond-by-millisecond detail.

Below the 950-millisecond level, where computerized trading occurs so quickly that human traders can’t even react, no fewer than 18,520 crashes and spikes occurred. The study’s authors call those events “financial black swans.”

The programs are designed to trade enormous volumes of stocks, bonds and other financial instruments at superfast speeds, taking advantage of second-to-second fractional price shifts and market trends.

It’s now estimated that high-frequency computer trading accounts for 70 percent of all equity trades. While some activity does occur at speeds with which humans can interact, much of it falls beyond the limits of human response time.

Ref.: Neil Johnson et al., Financial black swans driven by ultrafast machine ecology, arXiv, 7 February 2012.