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By Sean Duke
Science Editor
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The probability of a "megaquake" hitting Japan that could trigger enormous tsunamis and kill hundreds of thousands of people is now 82 percent, according to a Japanese government panel.
The Earthquake Research Committee has upped its estimate of the probability of such a devastating earthquake happening in an area called the Nankai Trough, an 800-kilometer (about 497-mile) undersea trench that runs roughly parallel to Japan's Pacific coast.
The trough lies along part of the "Pacific Ring of Fire," which runs roughly parallel to Japan's Pacific coast where two giant pieces of the earth's crust meet: the Eurasian plate and the Philippine Sea plate, with the latter "subducting" or moving slowly under the former and creating pressure and the potential for earthquakes as a result.
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The two plates can become stuck as they move past each other. This creates a massive buildup of pressure, which is only released when they break free from one another, move and re-align, causing potentially massive earthquakes.
The pattern of earthquake activity in the region over the last 1,400 years has seen "megaquakes" happening in the Nankai Trough every 100 to 200 years, says the Japanese government's Headquarters for Earthquake Research Promotion.
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The History Of 'Megaquakes' In Japan
The last megaquake to hit Japan happened in 1946, which was felt across Japan and destroyed 36,000 houses in the southern part of the island of Honshu alone.
"It's been 79 years since the last quake, and the possibility of another quake occurring is rising every year at a pace of about one percent," an official of the Earthquake Research Committee's secretariat told the French news agency, AFP.
According to previous Japanese government estimates, the smaller islands off the coast of Japan could be swamped by a tsunami over 100 feet high, while huge waves could hit the densely popular areas on the main islands of Honshu and Shikoku within a few minutes.
The Japan Meteorological Association last August issued its first-ever "megaquake" advisory under the rules that were drawn up after the devastating earthquake and tsunami of 2011, which killed 18,500 people. At the time, the Association said that the chances of a megaquake were higher than normal after a 7.1 magnitude earthquake hit.
This advisory lasted a week but resulted in emergency buying and shortages of rice and other foods.
In 1707, all segments of the Nankai Trough ruptured at once, unleashing an earthquake that remains the nation's second-most powerful on record and which triggered the last eruption of Mount Fuji.
At the end of World War II, Japan had to contend with two megaquakes that occurred along the Nankai trench in 1944 and 1946.
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