Japan's Quake, Tsunami Could Have Lessons For U.S.

The huge quake and tsunami that struck Japan occurred along what geologists call a "subduction zone." That is the kind of fault line where quakes generate big tsunami. There is one like it along the northwest coast of the United States. Geologists say it could go any time and wonder if we're prepared.

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The tsunami created by yesterday's earthquake in Japan rolled across the Pacific in about twelve hours. Six-foot surges pushed up onto Hawaiian beaches. Seaside towns along the west coast of the U.S. were evacuated. In some places, the tsunami wrecked marinas and boats.

The tsunami warning system for the Pacific Ocean appears to have worked well, though in Japan there may not have been time to heed the warnings. As NPR's Christopher Joyce reports, there could be a lesson here for Americans living on the West Coast.

CHRISTOPHER JOYCE: Evacuations started early yesterday morning in Hawaii and along the West Coast of the U.S. Mostly, the tsunami was mild, although in towns like Crescent City and Santa Cruz in California, marinas got beaten up and boats got piled up. There was widespread devastation in Japan, however.

The country sits on the edge of the ring of fire - a line of faults that etches a circle into the Earth's crust around the Pacific Ocean. Yesterday's quake was just the kind that creates tsunamis.

Eric Geist is a geophysicist with the U.S. Geological Survey.

Mr. ERIC GEIST (Research Geophysicist, U.S. Geological Survey): This was what's called a subduction zone earthquake, that involves a thrusting motion pushing up and pulling down the sea floor. And the ocean above the sea floor, of course, responds in kind and generates the tsunami.

JOYCE: A large expanse of the sea floor thrusts itself up by about 20 feet, tossing the ocean above it like a chef tosses a pizza crust. That sent tsunami waves racing out from the fault line. Japan's highly sophisticated quake and tsunami warning system detected this right away. So did the Pacific warning system operated by the U.S.

Pressure sensors, seismometers and tide gauges litter the ocean. Warnings went out within minutes of the quake, but it struck less than 100 miles offshore. Geist says the tsunami, moving at over a hundred miles an hour, left little time for evacuation.

Mr. GEIST: On the order of 15 minutes, somewhere less than an hour certainly, I don't think it was the quickest arriving tsunami; there's been some tsunamis in Japan that have arrived in, like, five minutes, but it was a short amount of time.

JOYCE: With only 15 minutes, people would have had to react with their feet.

Mr. GEIST: I think mostly people would have relied on the natural warning signs and, of course, the strong ground, very strong ground, shaking in this case and any ocean recession that occurred before the tsunami.

JOYCE: Often the ocean noticeably recedes along a coastline just minutes before a tsunami hits. Scientists in the U.S. say this quake and tsunami should be a wake-up call for Americans on the West Coast. The Cascadia subduction zone is an undersea line of faults that runs parallel to the northwestern coast, and it's very similar to the one that just ruptured off Japan's coast. It's close to shore and it ruptured in the year 1700.

Dr. ROBERT YEATS (Professor of Geology, Emeritus, Oregon State University): The reason we know the date of it is because it was recorded in Japan.

JOYCE: Robert Yeats is an emeritus professor of geology at Oregon State University. He says the 1700 quake was a mirror to the one yesterday. It was here, along the Cascadia subduction zone. The tsunami was documented in Japan.

Dr. YEATS: In all the records of temple officials, they called it an orphan tsunami.

JOYCE: Orphan because there was no earthquake in Japan, so they didn't know where the tsunami had come from.

Yesterday, Americans had almost 12 hours' notice of the tsunami. We won't have nearly that much if the Cascadia zone ruptures. And Yeats says a lot of Americans aren't paying attention.

Dr. YEATS: For example, I was looking at TV footage off seaside in Northern Oregon and there were some people walking on the beach, you know. And there was a woman running.

JOYCE: Yeats and other scientists say, no matter how good our warning system is, safety may come down to your feet - to feel the quake, and to get you out of the danger zone.

Christopher Joyce, NPR News.

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