5:15 PM - 6:45 PM
[MTT38-P05] Infrasonic signals likely to be caused by the tsunamigenic events around Tori-shima on 9 October 2023
Keywords:Infrasound, T-phase, Submarine volcano, Comprehensive Nuclear-Test-Ban Treaty
From 04:00 to 06:30JST on 9 October 2023, T-phases, which is acoustic wave converted from seismic wave traveling under the sea, were observed by seismometers around Tori-shima at least 14 times, although their hypocenters couldn't be determined by Japan Meteorological Agency due to its too small magnitude. Despite small magnitude, tsunami presumably excited by those events was observed on islands and coasts of Pacific Ocean in Japan.
According to the report from the Earthquake Research Committee of the Headquarters for Earthquake Research Promotion, those T-phases were estimated to be originated by the events which the US Geological Survey(USGS) determined its hypocenters near Sofugan located in the sea around Tori-shima. Since floating pumices were found near those events later, it is thought that some kind of volcanic activity may have occurred under the sea, but the cause of those events is currently still unknown.
After T-phases were observed at Chichi-jima, infrasonic signals were repeatedly detected at infrasound observatory of Comprehensive Nuclear-Test-Ban Treaty(CTBT) in Isumi, Chiba prefecture and infrasound sensors installed by Japan Weather Association(JWA) in Toyohashi, Aichi prefecture. As a result of array analysis, those signals were estimated to have come from the direction of the events described above. Furthermore, since those signals were observed at intervals of several minutes, similar to the T-phase, it is considered that infrasound were excited by the events that was the source of the T-phases mentioned above, then arrived to Isumi and Toyohashi respectively.
In addition, based on the result of ray tracing using upper-air observation data at that time, it is consistent that the infrasound propagated to Isumi and Toyohashi through near the ground surface or duct between the surface and the thermosphere.
Thus, it is considered that infrasonic signals observed at Isumi and Toyohashi are likely to be caused by a series of events near Torishima, and excitation of such infrasound that can be detected far away suggests that explosive phenomenon like submarine volcanic activity may be involved as the source of it.
According to the report from the Earthquake Research Committee of the Headquarters for Earthquake Research Promotion, those T-phases were estimated to be originated by the events which the US Geological Survey(USGS) determined its hypocenters near Sofugan located in the sea around Tori-shima. Since floating pumices were found near those events later, it is thought that some kind of volcanic activity may have occurred under the sea, but the cause of those events is currently still unknown.
After T-phases were observed at Chichi-jima, infrasonic signals were repeatedly detected at infrasound observatory of Comprehensive Nuclear-Test-Ban Treaty(CTBT) in Isumi, Chiba prefecture and infrasound sensors installed by Japan Weather Association(JWA) in Toyohashi, Aichi prefecture. As a result of array analysis, those signals were estimated to have come from the direction of the events described above. Furthermore, since those signals were observed at intervals of several minutes, similar to the T-phase, it is considered that infrasound were excited by the events that was the source of the T-phases mentioned above, then arrived to Isumi and Toyohashi respectively.
In addition, based on the result of ray tracing using upper-air observation data at that time, it is consistent that the infrasound propagated to Isumi and Toyohashi through near the ground surface or duct between the surface and the thermosphere.
Thus, it is considered that infrasonic signals observed at Isumi and Toyohashi are likely to be caused by a series of events near Torishima, and excitation of such infrasound that can be detected far away suggests that explosive phenomenon like submarine volcanic activity may be involved as the source of it.