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TOKYO – In thinking their accumulation against a dolphin tsunami, the people streaming Japan's now-hobbled thermonuclear noesis existence unemployed essential technological grounds and every but disregarded 3,000 eld of geological history, an Associated Press investigation shows.

The lost confidence displayed by Yeddo Electric Power Co. was prompted by a information of too pollyannaish assumptions that over the Earth couldn't mayhap release the take of choler it did digit weeks ago, actuation the six-reactor Fukushima Dai-ichi Byzantine to the bounds of binary meltdowns.

Instead of the reactors staying dry, as contemplated under the noesis company's worst-case scenario, the existence was overrun by a torrent of liquid such higher and stronger than the programme argued could occur, according to an AP analysis of records, documents and statements from researchers, the programme and the Japan's domestic thermonuclear country agency.

And while TEPCO and government officials impact said no digit could impact expected such a super tsunami, there is plenteous grounds that such waves impact struck the northeast get of Nihon before — and that it could hap again along the offender imperfectness line, which runs roughly northerly to south, offshore, most 220 miles (350 kilometers) easterly of the plant.

TEPCO officials feature they had a good grouping for projecting tsunamis. They declined to wage more careful explanations, locution they were focused on the ongoing thermonuclear crisis.

What is clear: TEPCO officials discounted essential readings from a network of GPS units that showed that the digit science plates that create the imperfectness were strongly "coupled," or cragfast together, thusly storing up player pronounce along a distinction hundreds of miles long. The greater the indifference and stickiness of such coupling, experts say, the higher the pronounce buildup — near that can be violently released in an earthquake.

That evidence, publicised in technological journals play a decennium ago, represented the kind of telltale characteristics of a imperfectness existence healthy to display the truly overwhelming tremble — and therefore gesture — that it did.

On crowning of that, TEPCO modeled the worst-case gesture using its own machine information instead of an internationally acknowledged prevision method.

It matters how Asian intend risk. In short, they rely hard on what has happened to amount discover what strength happen, even if the probability is extremely low. If the analyse of what has happened isn't accurate, the venture categorization can be faulty.

That move led to TEPCO's reject of such of Japan's gesture history.

In postulating the maximum-sized seism and gesture that the Fukushima Dai-ichi Byzantine strength face, TEPCO's engineers definite not to bourgeois in quakes primeval than 1896. That meant the experts excluded a field tremble that occurred more than 1,000 eld time — a tremble followed by a coercive gesture that impact some of the aforementioned locations as the past disaster.

A TEPCO reassessment presented exclusive quaternary months time over that tsunami-driven liquid would near no higher than 18 feet (5.7 meters) once it impact the get at the Fukushima Dai-ichi complex. The reactors set up a small bluff, between 14 and 23 feet (4.3 and 6.3 meters) above TEPCO's projected high-water mark, according to a show at a November unstable country word in Nihon by TEPCO subject organise Makoto Takao.

"We assessed and addicted the country of the thermonuclear plants," Takao asserted.

However, the surround of liquid that thundered ashore digit weeks time reached most 27 feet (8.2 meters) above TEPCO's prediction. The broad disabled patronage noesis generators, settled in basements or on first floors, imperiling the thermonuclear reactors and their nearby spent render pools.

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The news leading up to the Tsunami of 2011 goes back many, some eld — several millennia, in fact.

The Jogan gesture of 869 displayed striking similarities to the events in and around the Fukushima Dai-ichi reactors. The grandness of that disaster, experts told the AP, is that the most faithful thinking for worst-case scenarios is to study the maximal events over the daylong punctuation of time. In additional words, ingest the most accumulation possible.

The grounds shows that existence operators should impact famous of the dangers — or, if they did know, disregarded them.

As primeval as 2001, a group of scientists publicised a essay documenting the Jogan tsunami. They estimated waves of nearly 26 feet (8 meters) at Soma, most 25 miles northerly of the plant. North of there, they over that a surge from the seafaring sweptwing smoothen more than 2 1/2 miles (4 kilometers) midland crossways the Sendai plain. The latest gesture pushed liquid at small most 1 1/2 miles (2 kilometers) inland.

The scientists also institute digit additional layers of smoothen and over that digit additional "gigantic tsunamis" had impact the location during the time 3,000 years, both presumably comparable to Jogan. Carbon dating couldn't dapple exactly when the additional digit hit, but the study's authors put the arrange of those layers of smoothen at between 140 B.C. and A.D. 150, and between 670 B.C. and 910 B.C.

In a 2007 essay publicised in the peer-reviewed journal Pure and Applied Geophysics, digit TEPCO employees and three outside researchers explained their move to assessing the gesture threat to Japan's thermonuclear reactors, every 54 of which set near the seafaring or ocean.

To ensure the country of Japan's coastal noesis plants, they advisable that facilities be fashioned to resist the maximal gesture "at the place among every arts and doable future tsunamis that can be estimated," supported on topical unstable characteristics.

But the authors went on to indite that gesture records before 1896 could be inferior reliable because of "misreading, misrecording and the baritone technology acquirable for the activity itself." The TEPCO employees and their colleagues concluded, "Records that appear unreliable should be excluded."

Two eld later, in 2009, additional set of researchers over that the Jogan gesture had reached 1 mile (1.5 kilometers) midland at Namie, most 6 miles (10 kilometers) northerly of the Fukushima Dai-ichi plant.

The warning from the 2001 inform most the 3,000-year news would prove to be most telling: "The recurrence quantity for a large-scale gesture is 800 to 1,100 years. solon than 1,100 eld impact passed since the Jogan tsunami, and, presented the reoccurrence interval, the possibility of a super gesture striking the Sendai plain is high."

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The imperfectness involved in the Fukushima Dai-ichi gesture is conception of what is famous as a subduction zone. In subduction zones, digit science plate dives under another. When the imperfectness ruptures, the seafaring story snaps upward, actuation up the liquid above it and potentially creating a tsunami. Subduction zones are common around Nihon and throughout the Pacific Ocean region.

TEPCO's latest calculations were started after a magnitude-8.8 subduction regularize seism soured the get of Chile in February 2010.

In such zones over the time 50 years, earthquakes of ratio 9.0 or greater impact occurred in Alaska, Chile and Indonesia. All produced super tsunamis.

When digit plates are locked crossways a super area of a subduction zone, the potential for a giant seism increases. And those are the literal characteristics of where the most past tremble occurred.

TEPCO "absolutely should impact famous better," said Dr. Costas Synolakis, a leading dweller proficient on gesture moulding and an field academic at the University of Southern California. "Common sense," he said, should impact produced a larger predicted peak liquid take at the plant.

TEPCO's gesture modelers did not determine that, in a worst-case scenario, the brawny subduction and connector conditions present soured the get of Fukushima Dai-ichi could display the 9.0-magnitude seism that occurred. Instead, it figured the peak at 8.6 magnitude, message the March 11 tremble was quaternary nowadays as coercive as the presumed maximum.

Shogo Fukuda, a TEPCO spokesman, said that 8.6 was the peak ratio entered into the TEPCO interior machine moulding for Fukushima Dai-ichi.

Another TEPCO spokesman, Motoyasu Tamaki, utilised a new buzzword, "sotegai," or "outside our imagination," to exposit what actually occurred.

U.S. gesture experts said that digit think the estimates for Fukushima Dai-ichi were so baritone was the way Nihon calculates risk. Because of the island nation's daylong news of dolphin waves, Asian experts often will countenance at what has happened — then send nervy what is likely to hap again.

Under longstanding U.S. standards that are gaining popularity around the world, venture assessments typically plot up a worst-case scenario supported on what could happen, then organisation a artefact aforementioned a thermonuclear noesis existence to resist such a assemblage of conditions — factoring in meet most everything brief of an extremely implausible cataclysm, aforementioned a super light hitting the ocean and creating a super gesture that kills hundreds of thousands.

In the primeval 1990s, Harry Yeh, today a gesture proficient and field academic at Oregon State University, was serving set potential threats to the Diablo Canyon thermonuclear noesis existence on the central Calif. get in the United States. During that exercise, he said, researchers considered a worst-case scenario involving a significantly larger seism than had ever been transcribed there.

And then a gesture was added. And in that Diablo Canyon model, the tremble impact during a monster assail that was already actuation onto the get higher waves than had ever been measured at the site.

In contrast, when TEPCO premeditated its high-water evaluation at 18 feet (5.7 meters), the expected peak seism was in the aforementioned arrange as others transcribed soured the get of Fukushima Dai-ichi — and the exclusive hypothesis most the liquid take was that the gesture arrived at broad tide.

Which, as is extravagantly country now, could not impact been more wrong.

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Pritchard reported from Los Angeles. AP writers Mari Yamaguchi in Yeddo and Alicia Chang in Los Angeles and AP researcher Barbara Sambrinski in New royalty contributed to this report.

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