沈むニューヨーク、高層ビルの重さで地盤沈下　米研究

【ニューヨークＡＦＰ＝時事】米ニューヨーク市の一部が、超高層ビルの重さのせいで徐々に地盤沈下しているとする研究結果がこのほど、学術誌「アースフューチャー」に発表された。気候変動による海面上昇や洪水への脆弱（ぜいじゃく）性がさらに高まると指摘された。（写真は米ニューヨーク・ロウアーマンハッタンの街並み）
「コンクリートジャングル」と呼ばれるニューヨーク市のインフラが地盤に与える影響を研究している地質学者らは、同市の１００万棟を超える建物の総重量が約７億６２００万トンの下方圧力になると推計した。
　ＣＮＮによれば、これは燃料を満載したボーイング７４７－４００型機、約１９０万機分の重量に相当する。
　ニューヨークは年平均１～２ミリ沈下していると、論文は結論付けている。ただし地盤が柔らかい場所や埋め立て地の沈下ペースは年平均４．５ミリにもなるという。
　論文の主著者を務めた米地質調査所の地球物理学者トム・パーソンズ氏は、高層ビルを減らしても問題は解決しないとＡＦＰに語った。
　同氏は「ニューヨークと米東海岸の広範囲で起きている地盤沈下の主な原因は地殻変動で、これを止めることはできない」とその理由を説明した。
　ニューヨークでは地盤沈下によって、地球全体の気温上昇と氷冠の融解によって起きる海面上昇の影響が深刻化すると考えられている。
　海面上昇を研究する専門家団体「Ｓｅａ Ｌｅｖｅｌ Ｒｉｓｅ．ｏｒｇ」によると、ニューヨーク周辺の水位は１９５０年比で約２３センチ高くなっている。
　また市当局は２０５０年までに２０センチから、多いところで約７６センチの海面上昇が起きると予測。ニューヨーク州はすでに数千億円を投じて防潮堤の建設や道路のかさ上げ、排水システムの改善などを行っている。
　パーソンズ氏は、ニューヨークの一部がいつ水没するかは予測できないが、それは必ず起こると述べた。 【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2023/06/01-17:18）

If New York is the city that never sleeps then how's this for keeping you up at night? It is also sinking.
The Big Apple is gradually going down partly because of the weight of the skyscrapers that make the concrete jungle famous, a new study has found.
The descent makes the metropolis more vulnerable to rising sea levels and coastal flooding caused by climate change, the researchers noted.
The paper, published this month in the Earth's Future journal, sought to estimate how the city's vast infrastructure impacts subsidence.
Subsidence is the sinking of land mass caused by either natural processes such as erosion or human activity like mineral extraction.
The geologists calculated that New York's more than one million buildings added up to a total mass of 1.68 trillion pounds (762 billion kilograms) of downward pressure on the earth.
CNN said that was equivalent to roughly 1.9 million fully fueled Boeing 747-400s.
The report concluded that America's financial capital is sinking at an average rate of one to two millimeters per year.
Some areas built on softer rock or artificial landfill were subsiding as much as four and a half millimeters per year, the study added.
But building fewer skyscrapers will not solve the problem, lead author Tom Parsons told AFP.
The primary cause of subsidence in New York and along much of the Eastern Seaboard is tectonic and cannot be stopped, said the geophysicist at the US Geological Survey.
The subsidence is set to exacerbate the impact of sea level rise caused by warming temperatures and the melting of the world's ice caps.
The organization Sea Level Rise.org says water levels around New York are nine inches higher than they were in 1950.
The city's government predicts that surrounding waters will rise by between eight inches (20 centimeters) and 30 inches by 2050.
The state is spending billions of dollars building sea walls, raising roads and improving drainage to mitigate the risks.
But low-lying areas have already felt the brunt of devastating floods caused by more intense storms.
Hurricane Sandy in 2012 killed more than 40 New Yorkers, destroyed approximately 300 homes and left tens of thousands of people without power.
Hurricane Ida in 2021 left more than a dozen people dead in New York City, many after they were unable to escape flooding basements.
Parsons said it was impossible to say when parts of New York will be under water but it will happen.
It's too difficult to predict even a rough time because while city subsidence is relatively steady, forecasts for sea level rise are uncertain and depend on expected future rates of greenhouse gas emissions, he told AFP.
New York is not the only major world city that is sinking.
Subsidence and rising water levels have fueled fears that Venice may one day be entirely submerged.
And Jakarta is sinking at such an alarming rate due to the excessive extraction of groundwater that Indonesia is relocating its capital.