東京都下面可能有長７公里断層

Last month the Yomiuri News on-line reported the following:

東京都心部に長さ７キロ・メートルの断層が存在する可能性が高いことが、専門家らによる地質調査でわかった。

　地震を起こす活断層かどうかは、さらに精密な調査が必要としている。埼玉県熊谷市で２０日開かれた日本第四紀学会で発表した。

　断層の存在が指摘されたのは、新宿区四谷付近から北区田端付近までほぼ南北に延びる区間。豊蔵勇・元日本活断層学会副会長らのグループが、建設工事や土木工事の際に行われた地質調査のデータ約１３００点を分析した結果、四谷―田端間の東側と西側で、同じ年代の地層の深さが大きくずれていることが判明した。

　豊蔵さんは「古い年代の地層ほどずれが大きくなっており、２０万年間に断層が繰り返し動いたとみられる。地下深部で地震を起こす断層とつながっている可能性もある」と指摘する。

（2012年8月20日22時09分 読売新聞）

(試譯文)

It turned out in the geological survey by specialists that there was a high possibility that a fault of 7 km in length existing in the center of Tokyo.

Whether there could be an active fault which could cause an earthquake still needed more precise investigation. The Japan Association for Quaternary Research that was held in Kumagaya-shi, Saitama announced this on the 20th (August).

The fault that was pointed out to exist was the section which mostly extending from north to south from near Yotsuya of Shinjuku-ku to near Tabata of Kita-ku. The group was formed by the former Japanese Active Fault Society vice president, Isamu Toyokura; as a result of analyzing about 1300 data of the geological surveys on the occasions of construction works or a public works, it was made clear that the depth of the stratum had greatly shifted on the east side and the west side between Yotsuya and Tabata, compared to other stratum of the same age.

Mr. Toyokura pointed out that "up to the old age stratum the gap is large and it is seen as that the fault had moved repeatedly in 200,000 years. There is a possibility that it is connected to the fault which causes the deep underground earthquake."

It is an interesting discovery. More research should be done on this observation.