Why did tsunami fires? :in the 1993 Hokkaido Nansei-Oki and the 2011 Tohoku-Oki earthquakes

Tsunami fires occurred on Okushiri Island following the 1993 Hokkaido Nansei-Oki earthquake and also on the Sanriku Coast following the 2011 Tohoku-Oki earthquake. However, the ignition mechanism of such tsunami fires remained unclear. When the tsunami fire broke out following the 1993 Hokkaido Nansei-Oki earthquake, NHK broadcast staff who were covering the natural landscape of Okushiri Island by chance captured the moment the fire's ignition in Aonae Harbor, Okushiri Island. We investigated the physical process leading to the tsunami fire by combining suspected phenomena with the eyewitness testimonies. One eyewitness said, "The offshore area looked shining white and bubbling. There were five fishing boats moored on the quay that were burning and being blown by a strong wind, and the boats drifted and set light to the gasoline of a car being tossed by the tsunami and eventually the fire spread to the center of the city." The NHK video footage shot immediately after the boat fires occurred allowed us to confirm that the fires were almost simultaneous with the tsunami hitting the quay and a phenomenon of shining white, which was consistent with the eyewitness testimony. The flammable whitish bubbles must have involved combustibles, specifically methane, being released by a submarine landslide. In fact, bacterial mats suggesting methane release have been found off the west of Okushiri Island, where the tsunami originated. A large amount of methane bubbles reached Aonae Harbor together with the tsunami-induced wind, violently colliding with the quay wall, resulting in the generation of a large electrical potential difference between the mist and the sea surface, and the methane then electrostatically ignited, illuminating white. The methane bubbles accumulated on the boat decks and then ignited, causing the ignition of the oil/gasoline from a broken fuel tank besides that of the car and the car. A similar explanation can be constructed for the tsunami fire following the 2011 Tohoku Earthquake.