Geologists warn another earthquake could tear Tokyo in two after weakening of fault line below capital
By Daily Mail Reporter
Last updated at 5:15 PM on 21st March 2011
Geologists have warned that another powerful earthquake could inflict terrible damage on Tokyo because the Size 9 monster which struck on March 11 has altered the earth's surface.
The quake has put pressure on the fault lines near the Japanese capital and experts have suggested that a size 7.5 magnitude earthquake could hit.
The structure of the tectonic plates and fault lines around the city makes it unlikely that Tokyo, home to 13million people, would be hit by a quake anywhere near the intensity of the one 10 days ago, said Roger Musson of the British Geological Survey.
Bustling: The busy Japanese capital Tokyo has 13million people living in its centre - and it could be hit by another earthquake very soon熙熙攘攘：繁忙的日本首都東京有一千三百萬人生活在它的中心 - 和它可能很快被另一場地震襲擊
But given the vast population - the capital and its surroundings are home to 39million people (including in the suburbs) - any strong tremor could be devastating.
'Even if you've got, let's say, a 7.5, that would be serious,' the seismologist said.
Japan is located on the Ring of Fire, an arc of volcanoes and fault lines spanning the Pacific Basin, and is regularly hit by earthquakes.
But before the last quake - the largest to hit the country since it started keeping records 130 years ago - few geologists considered Japan to be a strong candidate for a 9-plus earthquake, said Andrew Moore, of Earlham College in Richmond, Indiana.
There is mounting evidence, however, that Japan has been struck by several severe quakes in the last 3,500 years - most in the northern reaches of the country.
Sand deposits indicate that several quakes have spawned 30-foot-high (9-metre-high) waves that slammed into the northern island of Hokkaido, he said, the most recent in the 17th century.
Similar deposits underlie the city of Sendai - the area rocked last week - with the most recent from an 869 A.D. tsunami that killed 1,000 people and washed more than 2.5 miles (three kilometres) inland.
And even weaker quakes that hit Tokyo in the past have caused significant damage.
Ring of fire火圈
Earthquake graphic地震圖形
But the tremor from March 11 changed the coastal landscape - and not just above sea-level.
It created a trench in the sea floor 240 miles long (380 kilometres long) and 120 miles wide (190 kilometres wide) as one tectonic plate dove 30 feet (nine metres) beneath another, said Eric Fielding of NASA's Jet Propulsion Laboratory.
While that relieved stress at the breaking point, it appears to have piled pressure on to adjacent segments, said Brian Atwater, a geologist with the U.S. Geological Survey.
That added strain could now trigger a strong, deadly aftershock on Tokyo's doorstep.
It's a common occurrence after strong quakes and happened after the 2004 mega-earthquake and tsunami off Indonesia that killed 230,000 people in a dozen nations.
Three months later, an 8.6-magnitude quake erupted farther down the fault line, killing 1,000 people on sparsely populated Nias island.
'But it's difficult to say,' said Atwater. 'There are good examples of such stresses leading to other earthquakes, big earthquakes, and there are good examples of that not happening.'
Scientists are studying the March 11 quake and ongoing seismic activity to determine where new strains might be building.
'When the main shock is this big, you get a football-shaped region where aftershocks are fair game. It extends in all directions,' including toward Tokyo, USGS seismologist Susan Hough and other experts said.
But, they acknowledge, it's hard to keep up.
Ross Stein, of the USGS, said: 'We are drinking from a fire hose here. The input data keeps changing and augmenting.'
http://www.dailymail.co.uk/news/article-1368405/Geologists-warn-powerful-earthquake-strike-Tokyo-disaster-weakened-fault-line-near-capital.html
英專家警告：板塊下移九米 東京倘遇7.5級地震恐擘開
(星島)2011年3月23日 星期三 05:30
(綜合報道)
(星島日報 報道)英國 地質專家昨日警告，「三一一」九級大地震對日本 東京 附近的地震帶斷層線構成更大壓力，東京面臨七點五級地震打擊可能被撕裂。東京高樓大廈林立，七點五級地震對東京一千三百萬人口來說，破壞力會相當驚人。
英國地質勘探局（British Geological Survey）專家馬森（Roger Musson）指，地震帶和板塊活動不同，東京不會遇到像三月十一日東北發生的九級地震，但三一一強震改變了海岸地形，顯示地震可能再次轉為活躍，東京很可能發生規模達到七點五級的大地震。
對日本人來說，地震好像「下雨一樣」多而且密。日本位處名叫「太平洋火環」地震帶，每年發生逾千宗地震，六級以上地震佔全球同類地震兩成。日本東北部過去經常地震，但百多年來未發生過九級地震，很少地質學家會作此預測。今次強烈地震，意味地殼可能已發生變化，斷層線更接近東京。今次強地震令其中一塊板塊向下移動九米，造成板塊之間有強大壓力，這壓力一釋放，就可能造成強烈地震。英國地質學家預測，東京可能發生七級以上強震。專家強調，現階段仍要研究各板塊移動情況，分析數據後才可預測地震發生時間和強度。
東京人買地震求生包
東京跟日本北部情況不同，發生稍強地震就足以造成重大影響，主要原因是：東京人口密度高，高樓大廈林立。不少東京的城市人已擔心強震會來臨。傳言在Twitter和網上不斷流出，東京人既要到網站每天更新核輻射 水平，亦要到商店買求生用電筒等用品，弄好地震求生包作好準備。
街上多了人以自行車代步，避免一旦地震來襲被困於地鐵 內；有人戴頭盔保護自己，或穿上平底鞋以準備地震時要徒步數小時回家，甚至下載iPhone地震提示軟件，務求一遇上地震，就迅速應變。
日本東北部昨日發生連串強烈餘震，令災民陷於高度緊張。美國 地震勘探局報告顯示，昨日在兩個半小時內，於日本東北部海嘯災區對開水域先後發生兩次六點六級及一次六點四級強震，當局沒有發出海嘯警報，也未有傷亡損毀報告。
http://hk.news.yahoo.com/article/110322/3/ne5t.html
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