Tsunami Damage To Oil Storage Tanks in the Mw9.0 2011 Tohoku, Japan Earthquake

Abstract eng:
The Mw9.0 2011 Tohoku, Japan earthquake tsunami damaged 418 oil storage tanks located along the Pacific coast of the Hokkaido, Tohoku, and Kanto Districts of Japan. A wide variety of damage was observed, including movement and deformation of the tank body, scouring of the tank base and ground, sediment runoff from the tank mound, movement or structural fracture of the pipe, cracking of the oil-retaining perimeter wall, and scouring of the perimeter wall base and ground. In total, 157 of the 418 tanks were moved by the tsunami. The moved tanks were distributed in the Aomori, Iwate, Miyagi, and Fukushima Prefectures of the Tohoku District. In the Fukushima Prefecture, the tsunami with an inundation depth of 13 m moved two 9,800-m3 tanks with 7,400-m3 and 6,000-m3 heavy oil stored, respectively, causing a large amount of heavy oil to leak out of the tanks. In this study, by comparing the severity of damage with the inundation depths of the tsunami experienced by the oil storage tanks, a fragility curve projecting the damage rate (P) for the piping of the tank was presented in terms of an inundation depth ( η in m): P(η ) = Φ ((ln η − 0.98) / 0.48) , where Φ is the standard normal cumulative distribution function. A rough but easy-to-use method of predicting tsunami damage to an oil storage tank from a given inundation depth was also presented: (i) for inundation depths of less than 2 m, most tanks are safe, although some might suffer minor damage, (ii) for inundation depths of 2–5 m, tanks suffer damage to their piping, small tanks (capacity < 100 m3) and empty larger tanks may be moved, but non-empty larger tanks are not moved, and (iii) for inundation depths of greater than 5 m, most tanks are moved. The validity of the previously-proposed tsunami tank-movement prediction method was first examined. A comparison of the method’s predictions with the actual damage data from the 2011 Tohoku earthquake tsunami indicated a hit rate of 76%. The method was also observed to overestimate tank movement. Almost every misprediction was a safe error (a tank that did not actually move was predicted to be moved). Because of the high accuracy and the tendency to provide safe predictions, the method has potential applications in practical prediction of movement caused to oil storage tanks by tsunamis resulting from future earthquakes.

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