A STATISTICAL STUDY OF THE DAMAGE CAUSES OF COASTAL FORESTS IN THE 2011 GREAT EAST JAPAN EARTHQUAKE TSUNAMI

Abstract

 A number of coastal forests were heavily damaged by the 2011 Great East Japan Earthquake (GEJE) tsunami. Since the resulting wood debris potentially increased the damage in some coastal communities, it is essential to elucidate the limitation of coastal forests as a tsunami mitigation measure. Although some criteria based on a maximum inundation depth have been proposed, their applicability has not been thoroughly examined. Moreover, some case studies following the event suggested that explanatory varia-bles other than inundation depth, i.e., local topographic features around coastal forests, significantly af-fected the damage level of the coastal forests. This study aims to identify potential variables and statisti-cally relate them to the damage of coastal forests based on a numerical tsunami simulation and a dataset of forest damage collected after GEJE tsunami. Consequently, the followings were confirmed: 1) the probability of severe damage on coastal forests increases with the fluid force of tsunamis and an elevation gap in front of the forest due to seawalls or other local landforms, 2) the probability of severe damage de-creases with the elevation of the coastal forest itself. Additionally, a damage prediction model was con-structed based on the results above, which achieved higher accuracy than the existing method.