2nd UPDATE: Traders, Electronic Systems Tested By Tuesday's Quake

Exchanges' trading operations and electronic market systems stood firm through a 5.8 earthquake that struck Virginia early Tuesday afternoon, according to officials.

Some traders evacuated from exchange floors and offices, but infrastructure supporting a network of automated trading continued without a hitch following the strongest quake to hit the state in more than 100 years, according to the U.S. Geological Survey.

U.S. stocks briefly retreated after the quake shook the Washington, D.C., area and sent out tremors felt in New York and Detroit, but prices quickly rebounded. Oil and other industrial commodities briefly dipped while gold, already settled for the day, headed lower.

"It started rumbling and everyone looked around at each other," said Joseph Mazzella, managing director for equities trading at Knight Capital Group (KCG) in Jersey City, N.J. "We ran a diagnostic [on trading systems] behind the scenes but you didn't see even a blink on your screen."

Representatives for NYSE Euronext (NYX), Nasdaq OMX Group Inc. (NDAQ), BATS Global Markets, Direct Edge and the International Securities Exchange said that dealing in securities and stock options continued unabated following the earthquake.

The New York Stock Exchange's downtown New York trading floor wasn't evacuated, nor was Nasdaq's Philadelphia options-trading floor.

"It felt like there was a subway train going underneath the building," said Jonathan Corpina, senior managing partner of Meridian Equity Partners, a broker on the NYSE floor. Within 20 seconds it was "business as usual" again, he said.

Some traders departed the New York Mercantile Exchange floor, though no official evacuation was ordered. IntercontinentalExchange Inc. (ICE) did evacuate its New York floors where options on cotton and the U.S. dollar index are traded, and Direct Edge evacuated non-essential staff from its Jersey City headquarters.

The quake tested the high-tech infrastructure supporting stock and derivatives markets that are now heavily electronic. New York-area data centers run by NYSE Euronext and specialist firms such as Equinix Inc. (EQIX) and Telx Group Inc. saw no hitches affecting the trades and messages among exchanges, brokers and proprietary trading firms.

Spread Networks, which runs a high-speed fiber corridor between the New York and Chicago financial hubs, said its connections were unaffected by the temblor.

Facilities housing exchanges' matching engines and the servers used by traders to send orders into the market are built to withstand catastrophes such as earthquakes, fires, floods and lengthy power outages. NYSE Euronext over the past two years has spent about $500 million constructing facilities in New Jersey and the United Kingdom, with backup generators ensuring power continues to flow in the event of a blackout.

"The bones of the building need to be extremely durable for our purposes," said Michael Terlizzi, executive vice president of engineering and construction for Telx, who said he couldn't feel the quake from inside the company's facility on 8th Avenue in Manhattan.

Telx, which houses exchanges and telecom companies in its data centers, looks to repurpose buildings originally constructed to house heavy industry like printing presses, according to Terlizzi. "Right after power and fiber concentration, what we look for in a particular property are its structural attributes," he said.

Representatives for Citigroup Inc. (C) and J.P. Morgan Chase & Co. (JPM) said their trading operations were operating as normal and there were no major disruptions. J.P. Morgan said it allowed employees to leave its New York buildings voluntarily, but there were no forced evacuations and operations continued as normal.

The U.S. Geological Survey rated the earthquake at 5.8 late Tuesday afternoon, after revising it downward from earlier estimates.

-By Jacob Bunge, Dow Jones Newswires; 312-750-4117; [e-mail]

--Steve Russolillo, David Benoit and Daniel Strumpf contributed to this article.