10. A Method to Determine the Level 1 and Level 2 Tsunami Inundation Areas for Reconstruction in Eastern Japan and Possible Application in Pre-disaster Areas

After the 2011 tsunami, a new approach to land use planning was introduced and is starting to be applied in some areas of Japan. Depending on the characteristics of the tsunami hazard, an area that is likely to be affected by high-frequency but low-impact tsunamis is identified as a ‘Level 1’ tsunami inundation area. An area that is likely to be affected by low-frequency but high-impact tsunamis is identified as a ‘Level 2’ tsunami inundation area. The countermeasures adopted in the two areas are different. The improved design of physical structures will be used to minimize the medium-to-low impact of tsunamis on people and properties in tsunami inundation Level 1 areas. Because the coverage of the flooded area is much wider in tsunami inundation Level 2 areas, improvements to the evacuation facilities and better education are the major efforts to save lives because man-made structures may not be able to significantly reduce the potential risks. This paper proposes a method to distinguish the boundaries between tsunami inundation Level 1 and 2 areas. We first use numerical simulations to establish a framework that classifies areas as Level 1 or Level 2 in a post-disaster area. Next, we examine the possibility of applying similar techniques to a pre-disaster area. We demonstrate that distinguishing areas of tsunami inundation Level 1 and Level 2 is not only important for the reconstruction of the post-disaster areas but also necessary to mitigate future tsunamis in pre-disaster areas.