Hidemasa Ohta

Landslides in Urban Residential Slopes Induced by the 2011 Off the Pacific Coast of Tohoku Earthquake

The preliminary report on landslides in residential areas induced by the 2011 off the Pacific Coast of Tohoku earthquake (M9.0) was conducted. Many urban landslides occurred in gentle residential slopes constructed as artificial valley fills (embankments) during this earthquake, particularly in Sendai, Shiroishi, Fukushima, Iwaki, and Tokai, from southern Tohoku to northern Kanto province. The landslides are mainly described based on the field investigations and are classified into five types. Some of the landslides that initiated in 2011 overlap with landslides induced by the earthquake in 1978. The repeated landslides at the same sites indicate that recent urban development and planning did not learn from the past disasters. Although countermeasures were constructed for landslides induced by the 1978 earthquake, serious landslides were found in same place in 2011. The disasters in 2011 have far-reaching ramifications for urban planning in Japan. We need a new design concept for urban development to minimize artificial geomorphological changes. The conceptual model of a “Counter line city” should both minimize risk of disasters and create a favorable natural environment in new urban regions along the Tohoku coast.

Development of support system to evaluate stability of the artificial fills for housings during earthquake

It is necessary to evaluate the relative risk of seismic sliding collapse to estimate damage effectively on the extensive land reclamation fills, and it is desirable to be evaluated from only common geographical information in all fills through the primary screening in accordance with the guideline for movement estimation investigation in extensive residential fill sites published by Ministry of Land, Infrastructure and Transport. Therefore, the authors conducted development and verification of the support system to be able to measure fill shape and evaluate relative stability for seismic sliding collapse.