About 44% of the people who evacuated from the giant tsunami of the East Japan Great Earthquake returned home before starting evacuation or dropped in before they reached a safe place. The author used interview data of survivors collected by the City Bureau, the Ministry of Land, Infrastructure, Transport and Tourism; and the Center for Space Information Science of the University of Tokyo, and analysed the purposes and consequences of returning home or dropping in by classifying the data into the rias coast area and the plain coast area, and into foot evacuation and automobile evacuation.
Notable among many outcomes were:
(1) When evacuees dropped in during evacuation, the time required to escape from tsunami inundation and reach a safe zone, became 3.2 times for foot evacuation in the plain coast area, and became 3.6 times for automobile evacuation in the rias coast area.
(2) Safety confirmation and rescue of family, relative, and acquaintance were the most common purposes of returning home and dropping in. For dropping in by automobile, these accounted for 58% in the rias coast area and 64% in the plain coast area.
(3) When the required times to reach a safe zone by foot evacuation and automobile evacuation were compared, the results were different according to the following combinations: evacuation in the rias coast or plain coast, evacuation after returning home or coming from home, and evacuation with or without dropping in. But, the data of number weighted averages of the required times for all combinations were almost the same for foot evacuation and automobile evacuation.
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