NH41C-1012 Why did tsunami fire? : in the 1993 Hokkaido Nansei-Oki and the 2011 Tohoku-Oki earthquakes

Yuji Enomoto* & Tsuneaki Yamabe (Shinshu Univ.)Shigeki Sugiura & Hitoshi Kondo (Geneses Res. Inst. Inc.) *Corresponding author, e-mail: [email protected]

130° 140° 150° 1993 M7.8 45° Aonae district a Hokkaido b c e f Nansei-Oki eq. Hokkaido M7.8 (Depth:35km) 5 4 Okushiri 3 5 4 3 2 island Hokkaido 40° 2 Tohoku Okushiri Tsunami 2011 M9 Tohoku-Oki eq. NHK Video 1 camera d g ̴10min 1 Okushiri 35° Island after ̴a few the e.q. min. Honshu at later

50km 22:17JST 30° Aonae 100m Fig.1 a right & g; the Okushiri-cho kirokusho on 1993 Hokkaido Nansei-Oki jisin:Tsunami simulation by Disaster Control Research Center, Tohoku University, :1b & e photo by Geographical Survey Inst.: c,d & f, NHK TV Special Program “Okushiri-toh karano Houkoku, aired at 20:00-20:50 on 16 July 1993.

Mysterious tsunami fires When the tsunami struck Aonae Mesh Labo-experiments, where a weight was a) Electrode To: have occurred at the Aonae district, a people who witnessed mA meter at electrode Falling bias 0 volt, dropped on the seawater bubbled with methane, this situation testify as follows: weight: or district of Okushiri Island, 1.5kg Electrostatic showed that splashed mists were positively Hokkaido ,Japan in the 1993 “Mists was rising, and sea Voltmeter charged (Fig.3 b & c). Hokkaido Nansei-Oki water was foaming” A b) c) I (uA) 200 earthquake (Fig.1a). About 10 1 2 3 similar scene could be observed 0 minutes after the M7.8 in the video footage shot during Acrylic pipe50mm 100 mA , Deionized water Time, sec. inner diameter, -4 earthquake occurrence, the the 2011 Tohoku-Oki 150mm height 0 st 0 0.5 1 1.5 2 2.5 current tsunami 1 wave attacked the earthquake at offshore of Miyagi Time, sec - -8 -100 Sea water

Aonae harbor, and all of a (Fig.2) . The bubbles might Chargedpotential, Volts

Micro -12 -200 sudden five fishing boats involve methane released from Foamed sea water burned out(Fig.1b-d) . the ocean floor. Bubble stone Fig. 3 a) experimental set up, b) charged potential and A few minutes later, the gusts Methane c) micro-current of splashed water. accompanying the tsunami 2nd wave blown, the burning Possible mechanism Tsunami wind + fishing boats were blown to the Generation of charged+++ +++ splash/mists +++ + shore, the fire spread to the Tsunami Methane bubbles + city area (Fig.1e-g). The mechanism why did the tsunami fires remain largely Land slide unexplained. Here we discuss Fig.2 Photo by Japan Ground the possible mechanism. Self-Defense Force, Tohoku) Fig.4 Fires might occur when the electrostatic energy exceeded the MIE of 0.28mJ for methane.