電柱を指標とした津波挙動分析 Tsunami Behavior Estimated from Damage to Utility Poles
The 2011 Tohoku-oki tsunami caused serious damage on the Pacific coast of the Tohoku district. This study focuses on fallen utility poles to clarify tsunami behavior in the northern and central Sendai coastal plain, because utility poles are distributed throughout the plain in high densities. The locations of utility poles are identified using high-spatial resolution satellite images acquired before the tsunami. The fallen poles and the direction in which they fell are interpreted by analyzing aerial photographs taken immediately after the tsunami. Fallen and/or missing utility poles are common within approximately 2 km of the coastline. The area corresponds to an inundation depth of 2 to 3 m. In addition, almost all of the poles fell to landward and are almost perpendicular to the shoreline. This indicates that they fell during the run-up flow. It seems that fallen poles in the northern part of the study area (Nanakita River to Sendai Airport) occur further inland than in the southern part (Sendai Airport to Abukuma River). In particular, fallen poles occur more than 2.5 km from the coastline at Yuriage to Kozukahara, Natori City, where the death rate was also relatively high. In contrast, fallen poles were less common within 1 to 1.5 km from the coastline at the southern part of Iwanuma City, where the death rate was relatively low. Although the height of the tsunami (i.e., scale of hazard) varied along the coast, the locations and scales of settlements near the shoreline specified the amount of rubble produced by the tsunami, and possibly influenced differences in the number of fallen poles.
地學雜誌 124(2), 227-239, 2015