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Is Japan's quake part of a cluster?

With massive earthquakes rocking many of the countries bordering the Pacific Ocean's "ring of fire," Simon Winchester, the author of "A Crack in the Edge of the World," warns that the Golden's State's San Andreas fault could rupture.

In the past year, massive earthquakes have rattled three corners of the Pacific plate — Chile, New Zealand, and Japan. Is the fourth corner of the plate — the west coast of North America — the next to go?

The possibility is getting a serious look — and air time. Journalist Simon Winchester, who often covers geological history, wrote a piece speculating about a major quake along the west coast in the March 13 issue of Newsweek and spoke about it this morning on the Today show.

According to Winchester, there is little doubt that earthquakes happen in clusters — a major event on one side of a tectonic plate is often followed weeks or months later by another major event on the far side of the plate.

"It is as though the earth becomes like a great brass bell, which when struck by an enormous hammer blow on one side sets to vibrating and ringing from all over. Now there have been catastrophic events at three corners of the Pacific Plate — one in the northwest, on Friday; one in the southwest, last month; one in the southeast, last year," he writes in Newsweek.

"That leaves just one corner unaffected — the northeast. And the fault line in the northeast of the Pacific Plate is the San Andreas Fault, underpinning the city of San Francisco."

Speaking with Meredith Vieira on the Today show, Winchester also emphasized the potential of a massive rupture on the Cascadia fault, which runs off the coast from Northern California to British Columbia. If that fault were to rupture, "it would cause not just terrifying problems on land, it would also generate a tsunami and that's a big, big problem," he said.

Earthquake clusters
John Rundle
, an expert on earthquake dynamics at the University of California at Davis, said evidence is mounting that major earthquakes do cluster in space and time, but that the New Zealand quakes were too small to count (magnitude 6.3 for Christchurch) in this current spate of events.

Even taking out the New Zealand events, there are still four major earthquakes at least as big as magnitude 8.6 in the last seven years – the two events in Sumatra in 2004 and 2005, the Chilean earthquake in 2010, and Japan. This is unusual, Rundle said.

"The question is, is it so unusual that these things are causal? We don't know that, but we used to believe that these things were independent and you would see random clustering, but this has become so pronounced that you have to think there might be some correlation to it," he told me today. "In fact most of our models that we use do show correlations of earthquake events."

Rundle added that he believes that earthquakes are correlated and these big events are correlated. The question is, are they correlated because there is a surge in plate motion or do these things just align in spurts when looked at over spans of thousands of years?

Regardless, he noted, that statistically speaking, faults along the west coast of North America are ripe to rupture. For example, the Cascadia fault ruptures about every 500 years. It last ruptured in 1700, an earthquake that triggered a tsunami that was felt clear across the ocean in Japan.

The last big event on the San Andreas in southern California was in 1857 and historical analyses show they occur about every 160 years, "which would lead one to think we are pretty much due for one of these magnitude 7 plus events on Carrizo Plain, which could obviously grow into a magnitude 8 if we are unlucky," Rundle said.

In Northern California, the biggest threat is on the Hayward fault, which last ruptured in 1868 and the recurrence interval is about 170 years. "So, we are definitely in the window where we could see a Hayward event," he noted.

Examined in this light, the west coast is due for a major quake whether or not a major event on one side of a tectonic plate can trigger a major event on the other side. Rundle noted that according to his modeling, there is a correlation between the clustering activity and the periodicity of when faults rupture. "There is a definite association," he said.

Aftershock concern
The concept of clustering, however, remains controversial. Andrew Michael, a geophysicist with the U.S. Geological Survey in Menlo Park, California, addressed the question of whether one major earthquake triggers the next in a summary about the Chile quake. There, he wrote, "probably not … the global rate of earthquake energy release shows little, if any, difference between times when very large earthquakes have been common and when they have not."

In an e-mail to me today, he said "[I] have revisited the calculations and the conclusions remain the same. There is no evidence of global large-earthquake clustering beyond localized aftershock sequences."

These aftershock sequences are what have Rundle the most concerned. The Japan earthquake was a magnitude 9. According to aftershock analyses, there should be one magnitude 8 aftershock and for each magnitude 8 there should be ten magnitude 7 earthquakes. So far, the largest aftershock was 6.8.

"Also, the aftershocks, appear to be migrating from the Sendai region down towards Tokyo. So I am extremely concerned that there may be a magnitude 8 earthquake in the relatively near future near Tokyo … and in that case you are talking about massive suffering," he said.

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John Roach is a contributing writer for msnbc.com. Connect with the Cosmic Log community by hitting the "like" button on the Cosmic Log Facebook page or following msnbc.com's science editor, Alan Boyle, on Twitter (@b0yle).