Updated

The earthquakes that hit Taiwan on Tuesday rocked communications in Asia and underscored the vulnerabilities of a system where huge amounts of data speed through the region in cables laid deep beneath the sea.

Banks and brokerages from Seoul to Sydney were affected by the outage, with analysts saying that even though a single glitch can trigger global problems, there is little choice but to rely on the underwater cable network.

"Right now, there's no other network that can compete with submarine fiber-optic cables in terms of reliability," said Jin Chang-whan, an analyst at CJ Investment & Securities in Seoul.

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The cables, which for the most part lie unprotected on the ocean floor, can be damaged by ship anchors, fish nets that scrape the sea bottom and even, in one case, sharks that gnawed on a line apparently due to its electromagnetic pulse, said the policy think tank Rand Corporation in a recent report.

The report predicted troubles in Taiwan could lead to major disruptions because it would be difficult to reroute data overland on the island.

Experts said there should be few problems in the cable systems as long as there are backup routes and carriers can cooperate in times of crisis.

Analysts said the disruption showed that most of the region's cable networks run along earthquake-prone geographic zones.

"People will start to say we can't let this happen again," said Frank Dzubeck, president of Washington D.C.-based telecoms consultancy Communications Networks Architects. "The issue here is parallelism. You've really got to have multiple paths. You can't lay all the cables in the same place."

Dzubeck added that the Internet bust in 2001 had hit expensive plans by various companies to lay undersea cables along new paths that were less likely to be affected by earthquakes.

Earthquakes occur frequently around Taiwan and Japan, which lie on a seismically active stretch of the Pacific basin.

Undersea fiber-optic cables account for more than 95 percent of international telecommunications thanks to their strength, capacity and connection quality, according to South Korean provider KT Submarine Corp.

One alternative would be satellites, which are costlier and do not provide as much capacity or quality of transmission as fiber-optic cables, analysts said.

Just last week, Verizon Communications Inc. (VZ) and five Asian companies agreed to invest $500 million to build a new cable network to directly link China and the United States.

BETTER THAN PIGEONS

Submarine cables have been around for about 150 years, with the one of the first lines being a well-insulated copper wire running under the English Channel. One alternative used at the time to transmit data was the carrier pigeon.

Now the cables hold a mass of tightly packed, flexible glass lines that can handle millions of telephone calls, which means that any damage can lead to major disruptions.

A country such as South Korea, the world's 11th largest economy, has 10 main undersea cables connecting it to the world, said KT Corp., the country's top fixed-line and broadband service provider. Seven of them were damaged by the quake.

India was highly vulnerable from damage to undersea cable links because it receives 80 percent to 90 percent of its bandwidth from the undersea network, industry officials said.

And neighboring Pakistan's sole undersea fiber-optic cable link with the outside world developed a serious fault in June 2005, virtually crippling data feeds, including the Internet, for 11 days.

"Internet service providers should think like bus companies," said Mohamed Shahril Tarmizi, executive director at Malaysian technology consulting company BinaFikir. "Instead of using just one route to get to a destination, it's more useful to have many routes."