Geomorphologic and Geologic Features of Landslides Induced by the 2011 Off the Pacific Coast of Tohoku Earthquake, in Shirakawa Hills, Fukushima Prefecture

The earthquake that occurred on March 11, 2011, off the Pacific coast of Tōhoku triggered many landslides on the natural slopes of Shirakawa Hills, Fukushima Prefecture, Japan. The landslide that occurred in Hanokidaira area caused the most damage and claimed the lives of 13 people; the failure occurred in the thick brown volcanic ash sediment layer on the hill slope and caused rapid soil flow across extensive areas, thereby increasing the resulting damage. There are a number of rapid landslides with similar characteristics even outside the Hanokidaira District; a volcanic soil layer collapsed and flowed a relatively long distance. The locations of many of these landslides are, like that in the Hanokidaira District, running from the crest slope to the upper sideslope located above a valley head and straddling knick lines. The slip surface is weathering tephra, and as in the Hanokidaira District case, presumably occurred with the part which was clay weakened by weathering.