Photograph by Noah Berger, AP
Published March 11, 2011
The deadly earthquake that struck Japan Friday sent a tsunami racing across the Pacific Ocean, causing flooding in Hawaii and prompting tsunami warnings along beaches in the Pacific Northwest and California.
(See Japan tsunami pictures from Friday.)
In Japan the magnitude 8.9 earthquake struck at 2:46 p.m., local time, along a segment of the undersea Japan Trench northeast of Tokyo, where the Pacific Ocean seabed dives under the Eurasian tectonic plate.
It's the fifth largest earthquake to be recorded anywhere in the world since 1900, according to the U.S. Geological Survey. (Get tsunami facts.)
Hours after the earthquake in Japan, the first tsunami waves struck Hawaii, where peak heights of between 7 and 11 feet (2 and 3 meters) have been reported on Maui and the Big Island. One hotel near Kealakekua Bay on the Big Island reported water in its lobby, according to the Associated Press, but overall damage was minimal.
On the U.S. mainland, the tsunami had been predicted to hit the northern Oregon coast first, at approximately 7:15 a.m. Instead, the waves came in first along the state's southern shores, at about 7:48 a.m., according to television reports.
But that discrepancy is nothing to be ashamed of, geophysicist Seth Stein told National Geographic News. "These models are very good today. They're not perfect, but they're getting better."
Wave heights in Oregon were relatively small—appearing to be about 3 or 4 feet (90 and 120 centimeters) on TV broadcasts. And unlike in Natori, Japan (picture), the wave did not come in as a wall of breaking foam. Rather, the tsunami in Oregon was much like the tide coming in and out, again and again, every 10 to 15 minutes.
Farther down the U.S. West Coast, California suffered damages to docks and boats.
At the northern port of Crescent City, "the harbor has been destroyed," city councilman Rich Enea told the Times-Standard newspaper, which reported crushed city docks and as many as 35 ruined boats.
Overall, though, reports suggest the state escaped the tsunami largely unscathed.
Tsunami Shaped by Seafloor
Though generally relatively small in the U.S., wave heights from the tsunami varied a bit, said Stein, of Northwestern University in Evanston, Illinois.
"What we're seeing is [the effect] of local seafloor topography. Some harbors will get big waves, and some will get small ones."
For example, many low-lying areas, which might otherwise seem vulnerable to flooding, are up rivers, which deflect and attenuate waves as they move inland—reducing the flooding, said Chris Goldfinger, director of the Active Tectonics and Seafloor Mapping Laboratory at Oregon State University.
By contrast, "other places have amplification by the local bathymetry. ... ," Goldfinger said via email.
On a broader scale, Northwestern's Stein added, "You have longer-range effects, like whether the wave gets focused by the bottom of the ocean" as it travels from Japan.
Authorities in Hawaii also noted that tsunami waves can bounce back and forth between the islands, prolonging the sloshing.
Trading One Earthquake Zone for Another
In a twist of fate, Oregon State's Goldfinger was at a seismology meeting in Chiba, Japan, listening to a talk about the 2004 Sumatran tsunami, when Friday's Japanese tsunami struck.
"We watched the tsunami come in live [on TV] in Sendai and Iwaki," he told National Geographic News by email. "Ships washing into town, amazing. Here in Chiba, you could literally feel the plates grinding."
But the big damage won't be from the grinding—it's the flooding that's most destructive, said Northwestern's Stein. "That was the case in Sumatra too, whereas the tsunami did enormous damage."
Tsunami Is Wake-up Call for U.S. West
Friday's tsunami, scientists said, is another wake-up call to residents of the coastal Pacific Northwest, where the tectonics are very similar to those in the Japan Trench. (Video: Tsunami 101.)
“This is an earthquake of the same type, with about the same magnitude and proximity that we face here in the Pacific Northwest from the Cascadia Subduction Zone,” geologist Robert Yeats said in press statement.
“What you are seeing in Japan today is what you will also see in our future. Except they are better prepared than we are," added Yeats, of Oregon State University.
Northwestern's Stein agreed, telling National Geographic News, "At some point in the future, one will have to think about a similar scenario on the [Pacific] Northwest."
(Related: To find out how Seattle could suffer a massive tremor, watch Mega Quake, airing Sunday, March 13, at 8 p.m. ET/PT on the National Geographic Channel in the U.S.)
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