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Posted at 10:20 AM ET, 03/11/2011

Japan earthquake is a seismic curveball

By Joel Achenbach

This is looking like the Big One for Japan. But it's in the wrong place, seismically and bureaucratically.

Here's what I typed up earlier this morning -- I'll update it soon.

The gist is, Japanese geologists have long forecast a huge earthquake along the subduction zone southwest of Tokyo. It had a name -- the Tokai Earthquake -- even though it hadn't happened yet. But now the nation's largest earthquake (magnitude 8.9) has hit, and it's 231 miles northeast of Tokyo.

The tsunami footage from Japan is dramatic and horrifying -- clearly this has devastated a large swath of the coast and there will be many fatalities. A scientist who specializes in tsunamis told me this morning that there will be at least 1,000 casualties. Reports say hundreds of bodies have found found in Sendai province, and that's easy to imagine, given the footage of cars being washed away.

Anyone on the West Coast should not presume that this will be as benign as the tsunami generated by the Chilean earthquake.

More to come...

***

This just in from the U.S. Geological Survey:

The 03/11/2011 earthquake (preliminary magnitude 8.9) near the east coast of Honshu, Japan, occurred as a result of thrust faulting on or near the subduction zone interface plate boundary between the Pacific and North America plates. At the latitude of this earthquake, the Pacific plate moves approximately westwards with respect to the North America plate at a velocity of 83 mm/yr. The Pacific plate thrusts underneath Japan at the Japan Trench, and dips to the west beneath Eurasia. The location, depth, and focal mechanism of the March 11 earthquake are consistent with the event having occurred as thrust faulting associated with subduction along this plate boundary. Note that some authors divide this region into several microplates that together define the relative motions between the larger Pacific, North America and Eurasia plates; these include the Okhotsk and Amur microplates that are respectively part of North America and Eurasia.

The March 11 earthquake was preceded by a series of large foreshocks over the previous two days, beginning on March 9th with an M 7.2 event approximately 40 km from the March 11 earthquake, and continuing with a further 3 earthquakes greater than M 6 on the same day.

The Japan Trench subduction zone has hosted 9 events of magnitude 7 or greater since 1973. The largest of these was an M 7.8 earthquake approximately 260 km to the north of the March 11 event, in December 1994, which caused 3 fatalities and almost 700 injuries. In June of 1978, an M 7.7 earthquake 35 km to the southwest caused 22 fatalities and over 400 injuries

***

Here's what I reported in a 2006 National Geographic story:

In Japan, government scientists say they have settled the question. Earthquakes are not random. They follow a pattern. They have detectable precursors. The government knows where Japan's big one will most likely strike. This is a country where the trains run on time, and earthquakes are supposed to do the same. "We believe that earthquake prediction is possible," says Koshun Yamaoka, a scientist at the Earthquake Research Institute of the University of Tokyo.

In fact, Japan has already named its next great earthquake: the Tokai earthquake. The government has identified and delineated by law the precise affected area--a region along the Pacific coast about a hundred miles (160 kilometers) southwest of Tokyo. After a series of small quakes in the Tokai area in the 1970s, scientists predicted that a major quake might be imminent there. The Japanese government passed a law in 1978 mandating that preparations begin for the Tokai earthquake.

Scientists have estimated a death toll of between 7,900 and 9,200 for a quake striking without warning in the wee hours. Estimated property damage: up to 310 billion dollars. At the Tokai earthquake preparedness center in Shizuoka, a map pinpoints 6,449 landslide locations. Another map shows where 58,402 houses could burn in quake-related fires. It's all remarkably enumerated. The only thing left is for the earthquake to happen.

There is, indeed, a plate boundary, called the Nankai Trough, that runs off the coast of the island of Honshu, where the Philippine plate is subducting beneath Japan. The boundary has generated massive earthquakes every 100 to 150 years. Two sections of it, side by side, broke in 1944 and 1946. But the section along Tokai hasn't generated a major quake since 1854, right about the time Commodore Perry sailed his warships into Tokyo Bay. The theory is that it's time for this part of the subduction zone to relieve its accumulated stress.

At the Earthquake Research Institute, Keiji Doi, who is in charge of public outreach, lays out the entire scenario. The land near Shizuoka is sinking toward the underwater trough at about five millimeters a year, indicating that strain is building up. "The earthquake occurrence is imminent, we believe," Doi says.

Up to this point, the Tokai tale is more a forecast than a prediction. But a precise prediction of time and place would be far more valuable for emergency planners. Thus has arisen the idea of "pre-slip," a notion that skeptics say is part science and part wishful thinking.

Naoyuki Kato, another scientist at the Earthquake Research Institute, says his laboratory experiments show that before a rock fracture gives way, it inevitably slips a little. He believes that what happens in a lab at small scale will also happen on a fault hundreds of miles long and running deep into the crust, just before the next big one.

The government has an action plan built around pre-slip. Strain meters are embedded in the ground all over the Tokai area. If one or two meters show anomalies, scientists will confer and schoolkids will go home. Three anomalies will put the country on high alert. Police, soldiers, and firefighters will race to the border of the vulnerable area. The prime minister will make a speech and say that an earthquake is imminent. Posters outlining this plan show a cartoon prime minister sitting at a desk with hands folded, looking very worried, but very much in charge.

Yet none of the experts on the Tokai earthquake describe this scenario with much conviction. Press them, and they will admit their uncertainty. Yamaoka and Kato, for example, are both bullish on pre-slip, yet they also say it may be too small to be detected.

Robert Geller, an American geophysicist who works half a mile (0.8 kilometers) away at the University of Tokyo's school of science, is less circumspect. Geller has been in Japan for decades and has made "bashing earthquake prediction," as he puts it, a passionate hobby. He calls the prediction program "faith-based science." Pre-slip, he adds, "has never been verified to exist for actual earthquakes."

Geller's skepticism is not just a case of American outspokenness. Hideki Shimamura, an earthquake scientist at Musashino Gakuin University near Tokyo, is almost as blunt. "There may be pre-slip, but rather doubt it," he says, adding that few researchers are willing to question the focus on Tokai lest they lose funding. The situation has potentially lethal consequences, he says: Prior to the Kobe earthquake in 1995, which killed 6,400 people, few people or public officials in Kobe had any inkling that they were vulnerable. Earthquakes were mainly someone else's problem--far to the east, in Tokai. "They didn't prepare," Shimamura says.

By Joel Achenbach  | March 11, 2011; 10:20 AM ET
 
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