Possible Mechanism of Tsunami Fires That Occurred in the 2011 Great East Japan Earthquake

Tens of minutes after the 2011 Great East Japan earthquake, blackened tsunamis hit wide areas of the Sanriku coast, causing fires and devastating fire disasters. Although various research studies have been reported on this disaster, the potential mechanism of the tsunami induced fires remains unclear. Therefore, in this study, we examined the time series of information and studies that contribute to the clarification of the tsunami-fire mechanism that occurred in Natori City, Yuriage 7-chome and Kesennuma City, Shishiori district. Based on our previous research on the tsunamifire that occurred in the Aonae harbor of Okushiri Island during the 1993 Hokkaido Nansei-Oki earthquake, we proposed a new model that the tsunami-fire occurred in the following process. (1) The blackened tsunami that engulfed the sludge deposited on the seabed offshore also swept up the methane generated in the sludge, and white bubbles containing methane were carried to coastal area with assist of the tsunami wind. (2) The methane bubbles collided with man-made objects such as quay wall on the coast, bursting, and electrified mist rose up, which result in the electrostatic ignition of the methane, or (3) Methane bubbles are trapped under and/or in the narrow gaps of aggregated debris floating on the sea surface, and the electrostatic static ignition of the methane occurs by collisional friction between debris with different electrification series. (4) Due to the process of (1) or (2), any flammable combustibles in urban areas caught fire and spread, which result in a large-scale fire.