A February map from the U.S Geological Survey shows the estimated range of the great Cascadia earthquake of 1700.
A massive earthquake like the one that unleashed a giant tsunami and killed nearly 16,000 people in Japan a year ago not only could happen here in the U.S., but probably will — and relatively soon in terms of seismological history.
The Tohoku earthquake was the most closely monitored in history, yielding an unprecedented breadth of data, geophysicists and seismologists say. And for residents of the Pacific Northwest, the new data should be worrisome.
"It's just like Japan, only a mirror image," said Gerard Fryer, a geophysicist at the University of Hawaii and the Pacific Tsunami Warning Center.
The disaster in Japan occurred because of stress from the Pacific tectonic plate sliding below Japan, according to new research discussed last month at the annual conference of the American Association for the Advancement of Science in Vancouver, British Columbia.
The lead researcher, John Anderson, a geophysicist at the University of Nevada-Reno, said the plates locked together, slowly pushing Japan westward.
Ben Gutierrez and Lisa Kubota of NBC station KHNL in Honolulu contributed to this report by M. Alex Johnson of msnbc.com. Follow M. Alex Johnson on Twitter and Facebook.
The plates released catastrophically on March 11, 2011, creating a magnitude-9.0 earthquake and tsunami waves that topped 100 feet, said Anderson, who spent most of the past year in Japan as a visiting research professor in Tokyo.
While most Americans probably think the San Andreas fault running through California poses the greatest threat of unleashing a killer mega-quake, data from the Japanese quake indicate that the distinction actually belongs to the Cascadia fault line, which runs through southern Canada, Washington and Oregon to Northern California, Anderson said at the conference.
Biggest threat zones
The biggest threats of a U.S. mega-quake (generally defined as one of magnitude 7.0 or greater) lie along three fault lines:
The Cascadia subduction zone stretches from northern Vancouver Island through Seattle and Portland, Ore., to Northern California, separating the Juan de Fuca and North America plates. Giant quakes are believed to occur there every 300 to 600 years; the last was Jan. 26, 1700. Recent research suggests the region could have a 37 percent chance of a magnitude-8.2 quake or greater in the next 50 years.
The San Andreas transform fault runs the length of California, separating the Pacific and North American plates. The last mega-quake was in 1906 near San Francisco, but large earthquakes of magnitude 6.0 or above are relatively common in historical terms, having occurred as recently as September 2004 near Parkfield.
The New Madrid seismic zone stretches southwest from New Madrid, Mo. (pronounced MAD-rid), and is most active in Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri and Tennessee, where it regularly produces small- to medium-intensity temblors. Three magnitude-8.0 quakes are believed to have occurred in the region from December 1811 to February 1812; had Memphis, Tenn., existed at the time, it likely would have been destroyed. Since then, the largest earthquake was a magnitude-6.6 quake in October 1895 near Charleston, Mo.
msnbc.com research/M. Alex Johnson. Sources: NASA Astrophysics Data System, National Oceanic and Atmospheric Administration, Oregon State University College of Oceanic and Atmospheric Sciences, Scripps Institution of Oceanography, U.S. Geological Survey.
Like Fryer, he called the Pacific Northwest trench a "mirror image" of the Japanese trench — except potentially even more dangerous.
"In this mirror image, one can see that if the same earthquake occurred in Cascadia, the fault would rupture to a significant distance inland, since the Cascadia trench sits much closer to the coastline than the trench off the coast of Japan," Anderson said.
While some probability models predict that a Cascadia earthquake wouldn't rupture so far under the land, "if it does, the data from the Tohoku earthquake predict stronger ground motions along our West Coast than those seen in Japan," he said.
In layman's terms, what's happening is that the region "is being deformed because the plates are locked together, and the shoreline is sinking and the rest of the thing is being bent," Fryer said in an interview with NBC station KHNL of Honolulu.
Fryer said the big question is not whether a Japan-like quake will happen, but when.
A coastal Oregon town considers building a tsunami- and earthquake-proof city hall. Experts and residents debate whether the plan will work.
"Where are we here? Are we close or are we not close?" he asked. "I think the suspicion is that it could be sooner rather than later."
Anderson's research supports that conclusion.
Experts generally agree that last great Cascadia earthquake happened on Jan. 26, 1700. It generated tsunami waves that indicated that its magnitude was also about 9.0.
"Earthquakes of this size in the past may have recurred with intervals of as small as about 300 years," Anderson said at the AAAS conference last month. "So it would not be a scientific surprise if such an event were to occur in the near future. If you live in the Pacific Northwest, look at the videos of Tohoku as a reminder to be prepared."
In January, experts discussed lessons from the Japanese earthquake at a conference of the Cascadia Region Earthquake Workgroup.
The warnings come as the White House is proposing a 2013 budget that would cut $4.6 million from National Oceanic and Atmospheric Administration's tsunami programs. Much of that would come from the National Tsunami Hazard Mitigation Program, which funds evacuation maps, training and education efforts — important services given how deeply the Japanese quake and tsunami transformed the science of seismology.
"The Japan earthquake told us that a lot of what we understand about how earthquakes work is wrong," Fryer said. "Do we now have to go back and look at all of our evacuation maps and make sure that they're right? That's a question that's still unanswered, and that question would be answered with tsunami hazard mitigation program funds."
More on the Japan Quake-Tsunami from msnbc.com and NBC News:
- Prediction lessons from the Japan quake
- One year after Fukushima, Japanese town is frozen in time
- Japanese tsunami survivor, 79, looks ahead
- Tsunami Survivors: Struggling to live on, alone
- Japan Red Cross: Whole year wasted after tsunami
- Cosmic Log: Hear the soundtrack of a super-quake
- Nuke pill frenzy fizzles in U.S. as Fukushima fades
- Photo Blog: Panoramic images, then and now
- Japan disaster snarls U.S. nuke plant plans