Liquefaction Damage of The Tonegawa Basin Caused by The 2011 off the Pacific coast of Tohoku Earthquake

概要

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Significant liquefaction affected the Tonegawa basin as well as the Tokyo-bay area during the 2011 Tohoku-oki earthquake. This liquefaction caused undermining many house foundations and destroying infrastructure around these areas. In this report, we focus on the pattern of liquefaction in the Tonegawa basin and the probability of liquefaction occurrence in Kanto district during the 2011 Tohoku-oki earthquake. First we revealed the liquefaction pattern in the Tonegawa basin based on the field survey at 29 municipalities in Chiba and Ibaraki prefectures. The evidences of liquefaction were mainly found in the artificial ground created from the sea, pond, and river. Second we calculate the probability of liquefaction occurrence during the 2011 Tohoku-oki earthquake for each geomorphologic classification unit in whole Kanto district according to a variety of survey results including our own. The liquefaction probabilities of the 2011 Tohoku-oki earthquake are much larger than those of past earthquakes caused liquefaction.