On October 2023, 10, tsunamis with wave heights of several tens of centimeters were observed in Izu and the Ogasawara Islands and along a wide coastline from Kanto to Okinawa, even though no major earthquakes were observed. Regarding this unique tsunami (Torishima Near Sea Tsunami), which is thought to originate in the waters near Torishima in the Izu Islands, Assistant Professor Osamu Mitanhata, Professor Kenji Satake, Assistant Professor Shunsuke Takemura, and Associate Professor Shingo Watada of the Earthquake Research Institute, the University of Tokyo, and Hirosaki University Graduate School A joint research team consisting of Professor Takuto Maeda of the Graduate School of Science and Engineering and Senior Researcher Tatsuya Kubota of the National Research Institute for Earth Science and Disaster Prevention conducted the investigation.
As a result of analyzing the tsunami waveforms recorded by the "Undersea Earthquake and Tsunami Observation Network DONET," which is operated by the National Research Institute for Earth Science and Disaster Prevention and is installed on the seabed from the Kii Peninsula to the offshore of Shikoku, it was found that It was revealed that a total of 1 small tsunamis occurred in quick succession near Torishima. Because the peaks and troughs of these tsunamis overlapped, the wave height of the Torishima coastal tsunami, especially in the latter half, was amplified, reaching about twice the height of each individual wave.
It was also discovered that, at around the same time, multiple moderate-sized earthquakes with magnitudes of 70 to 4 occurred around the submarine volcano Sofu Rock, located approximately 5 km south of Torishima. This is thought to be the seafloor movement phenomenon that caused the 14 repeated tsunamis.
The results of this research are the first in the world to observe and demonstrate a rare phenomenon in which the seafloor movement phenomenon that generates tsunamis frequently occurs ten or more times within a few hours, and the tsunami wave height is amplified by the superposition of small tsunamis. This is what I did. In late October of the same year, floating pumice containing ejecta from volcanic activity was discovered in the surrounding waters from Torishima to Sofuiwa, suggesting a connection between the simultaneous occurrence of earthquakes and tsunamis and submarine volcanic activity. There is. It is hoped that the mechanism of the unknown seafloor movement phenomenon that caused the Torishima tsunami will be elucidated.
Paper information:[Geophysical Research Letters] Enigmatic tsunami waves amplified by repetitive source events near Sofugan volcano, Japan
