8.9 Quake Triggers Tsunami Across Pacific Ocean

March 11, 2011

Richard Harris

Download Story

Japan's northeastern coast was slammed by a strong earthquake and tsunami Friday. It appears most of the damage was caused not by the ground-shaking but by the tsunami it generated.

The 8.9 magnitude earthquake that struck off Japan was on par with the 8.8 magnitude earthquake that hit Chile around this time last year, but NPR's Richard Harris tells Renee Montagne that "a quake of this size can be devastating, or it doesn't necessarily have to be," because infrastructure preparations can mitigate some of the damage. So "the ground shaking is not necessarily the biggest issue," Harris says.

Harris says that looking at maps of the ground shaking, it's evident that there was shaking over a very large area of Japan, "but most of the shaking was moderate — it didn't hit the severe, violent marks that mark really devastating earthquakes from ground shaking."

An offshore epicenter like Friday's massive earthquake, which was centered around 80 miles east of the Japanese city of Sendai, raises the potential for generating underwater landslides or big waves that can propagate over thousands of miles of ocean.

Video reports from Japan have showed that water has washed ashore there, causing significant damage. And though much of Japan has been built to withstand strong earthquakes and tsunamis, Harris says that when the quake is so close to land, there's very little time to react.

Across the ocean, there's more time to prepare for a big wave, and buoys located in the Pacific have seen the wave spreading, measuring a rise of about three feet in some places. That may not seem like much of a problem in the ocean, but when the wave approaches land, it can rapidly become much larger, Harris says.

"A three foot wave in the ocean right now is a big, big concern, particularly for low-lying islands," Harris says. "So if you're looking across the south Pacific, all of those islands are potentially in Jeopardy."

The tsunami that raced its way through the Indian Ocean in 2004 had a death toll in the hundreds of thousands, as there was incredibly dense populations near the shoreline. "The population at risk is much smaller in the Pacific Ocean than it was throughout the Indian Ocean," Harris says, so "this could be very devastating to people in the Pacific Islands, but probably we're not going to be looking at numbers of that magnitude." Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.