Most Web sites are operational and the Internet remains available to support critical communication functions, Renesys CTO James Cowie wrote in a .

In the immediate aftermath of the earthquake off the Japanese coast, about 100 of Japan's 6,000 network prefixes -- or segments -- were withdrawn from service. But they started reappearing on global routing tables just a few hours later. Similarly, traffic to and from Japan dropped by about 25 gigabits per second right after the Friday quake, but returned to normal levels a few hours later. And traffic at Japan's JPNAP Layer 2 Internet exchange service appears to have slowed by just 10% since Friday, according to Renesys.

"Why have we not seen more impact on international Internet traffic from this incredibly devastating quake? We don't know yet," Cowie wrote.

An unknown number of people were killed and whole cities devastated by what was one of the worst earthquakes in over 100 years. The quake, which initially measured 8.9 on the Richter scale, generated a huge tsunami that inundated parts of Japan and put almost the entire Pacific coastline on a tsunami alert.

The effects of the quake, in terms of human loss and economic damage, are expected to be huge. The quake also . One reason Internet connectivity appeared to fare better could be that undersea cables remained relatively untouched by the quake, unlike in 2006 when an earthquake in Taiwan resulted in a large number of major cable breaks, Cowie said.