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For Japan, perched on the so-called Pacific “Ring of Fire,” a major earthquake is no great surprise. The country’s building codes and earthquake alert systems are among the most sophisticated in the world and have no doubt saved thousands of lives. Now, scientists in the Pacific Northwest, whose Cascadia fault holds eerie similarities to the one that triggered today’s quake in Japan, say the disaster may force them to reexamine their own earthquake preparedness.

“This earthquake is going to be the benchmark for the Pacific Northwest when the Cascadia fault breaks,” says seismologist John Vidale of the University of Washington, Seattle. “We know that it can have an earthquake of this magnitude. It’s a question of when, not if.”

The Northwest, like Japan, lies in a subduction zone in which one tectonic plate plunges under another–as opposed to a shear zone like that in California where plates rub past each other horizontally. Both types of quakes can be devastating, but only quakes in subduction zones cause tsunamis. The shock of the magnitude-8.9 earthquake that hit Japan this morning was its sheer intensity: Several experts have hypothesized that the last one of this magnitude struck Japan in 869 C.E.

The quake shows both the importance and the limits of planning ahead, says seismologist Robert Woodward of the Incorporated Research Institutions for Seismology in Washington, D.C. Studying earthquakes older than a few centuries is “incredibly hard forensics” that relies mostly on analyzing sedimentation caused by tsunamis, Woodward says. As a result, building codes are based mostly on smaller, more recent quakes and on geophysical monitoring.

But such hazard predictions can go only so far, Vidale says. They can warn how often and how strongly the ground will shake, but they can’t forecast the magnitude of any single event.

So far, Vidale says, the hazard predictions for Japan seem to have been much more accurate than they were for the tragedy in Christchurch, New Zealand. “We don’t know yet, but haven’t seen evidence of buildings collapsing,” he said—a factor that added to the death toll in New Zealand

Japan is not out of the woods yet, Woodward notes: Buildings and structures weakened by the first quake may not withstand aftershocks. But Vidale says the real danger Japan faces now is not aftershocks from this quake, but a second earthquake on a fault that runs near Tokyo, which now has more stress on it. “In all likelihood it won’t be for decades,” he says, “but the chance is a lot more than it was yesterday.”

Scientifically, Woodward expects the earthquake to be a gold mine of information for researchers in the future. Vidale says scientists will be scrutinizing Japan’s seismological data in the days leading up to the quake for patterns or foreshocks that could predict future quakes.

Vidale says a priority for earthquake researchers will be discovering whether Japan’s sophisticated warning system helped mitigate the damage. Seismographs picked up the first tremors and sent an automated warning to TV stations and other outlets 1 minute before the quake struck. The actual impact of the warning remains to be studied, but Vidale says planners in the Pacific Northwest should take it into account.

“This is a well-instrumented earthquake, in a comparable setting [to the Pacific Northwest], and I think we’re going to learn a lot,” Vidale says. He estimates that installing such a response system in the Cascadia region would cost about $50 million, plus at least $1 million each year to monitor.

Compared with up to $100 billion in economic damage which, at the time of writing, the United States Geological Survey is predicting for the catastrophe in Japan from shaking alone (not including tsunami damage), it may be a worthwhile investment.

Science Insider, 11 March 2011