非常に強い「長周期地震動」 過去２１年間に６地震で観測｜ニュース 動画 NHK News

Very strong 'long period ground motion' Observation with 6 earthquakes in the past 21 years



超高層ビルなどを大きく揺らす「長周期地震動」のうち、建物の構造に被害を及ぼすおそれのある非常に強い揺れが、過去２０年余りの間に６つの地震で観測されていたことが、専門家の分析でわかりました。リスクを認識し、対策を検討する必要があると指摘しています。

「長周期地震動」は、高い建物などを大きく揺らす周期の長い揺れで、６年前の東日本大震災では、震源から遠く離れた東京や大阪などの超高層ビルが１０分以上揺れ続けました。



このときは、ビルの柱などの構造に被害は出ませんでしたが、筑波大学の境有紀教授が去年５月までの２１年間に震度６弱以上の揺れを記録した全国の５１２の地震計のデータを分析したところ、全体の４％にあたる２１の地点で、ビルの構造に被害を及ぼすおそれのある非常に強い「長周期地震動」が観測されていたことがわかりました。



地震の数では合わせて６つで、平成１５年の十勝沖地震など沖合のプレート境界で起きる「海溝型地震」に加え、去年４月の熊本地震や平成１６年の新潟県中越地震などの「直下型地震」も含まれています。



境教授によりますと、非常に強い「長周期地震動」が高さ１２０メートルの鉄骨造の超高層ビルを襲った場合、柱が変形するなど、構造に深刻な被害が出るおそれがあるということです。

境教授は「これまでは非常に強い長周期地震動が観測された場所に、たまたま超高層ビルがなかったため深刻な被害が出なかったと考えられる」と述べ、今後はリスクを認識し、対策を検討する必要があると指摘しています。



Among 'long period earthquake motions' that greatly shake skyscrapers and the like, very strong tremors that may damage the structure of the building have been observed in the past six decades due to six earthquakes I understood by analysis of the house. It is necessary to recognize the risk and to consider countermeasures.

'Long period earthquake ground motion' is a shake with a period of great swaying of high buildings, etc. In the Great East Japan Earthquake six years ago, skyscrapers such as Tokyo and Osaka far from the epicenter kept swinging for more than 10 minutes.



At this time, the structure of the pillars etc of the building did not suffer, but Professor Noriko Naki of University of Tsukuba recorded 512 earthquakes nationwide which recorded a shake of less than 6 seismic intensity in the 21 years until May last year Analysis of the total data revealed that very strong 'long-period ground motion' was observed at 21 points, which is 4% of the total, which could damage the structure of the building. In addition to the 'trench type earthquake' occurring at the offshore plate boundary such as the 2003 Tokachi oki earthquake in 2003, the number of earthquakes in addition to the earthquake in Kumamoto last April and the Niigata Prefecture Chuetsu Earthquake 2004 'Direct type earthquake' is also included. According to Sei Baoda, if a very strong 'long-period ground motion' strikes a steel-made skyscraper with a height of 120 meters, there is a possibility that the structure will be seriously damaged, such as deformation of the pillar is. Professor Ban said, 'It seems that there were no skyscrapers in the place where very strong long-period seismic motion was observed so it happens that there were no skyscrapers by chance, so it seems that there was not serious damage, and in the future we will recognize the risk and take countermeasures We need to consider it.



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