公益財団法人 セコム科学技術振興財団
研究成果報告書研究課題名

複合型インフラサウンドセンサーの面的展開による津波防災情報伝達ネットワークの構築
Construction of information relay network for tsunami disaster prevention
with wide-spreading comprehensive infrasound sensors

研究期間
平成２８年４月～

令和

２年

３月

報告年月
令和

２年

６月

研究代表者
高知工科大学 システム工学群
山本教授

真行

Kochi University of Technology
Masa-yuki Yamamoto

Professor

Abstract
Infrasound, which is the core of this research, is low-frequency sound waves with a frequency ofless than 20 Hz, that are inaudible to the human ear, also known as micro-pressure waves. Due totheir large wavelengths, infrasound cannot be produced by objects as large as normal sounding
instruments. It is possible to be excited by the movement of a large geophysical object, such as asediment disaster. The system we have developed can be used to measure infrasound, thus, theinfrasound waves excited by various events can be precisely measured by using a planar array ofsensors. Various geophysical events can be detected remotely by checking time differences of soundarrival. An alert system with infrasound remote-sensing can be done in the near future, just as theemergency earthquake alert system are realized from the earthquake observation network. If anobservation network can be established, there is a possibility of transmitting important information
related to disaster prevention.
In this research project, comprehensive infrasound sensors that have already been developed by
the principal investigator and colleagues are used, and then they use it to measure the infrasound in
Kochi Prefecture as a model area. We have developed a dense wide-spreading observation networkwith the comprehensive infrasound sensors. At the preparatory research stage in FY 2016, they were
installed in five locations in Kuroshio Town, Kochi. In FY 2017, the project was spread to a total of 15
locations in Kochi Prefecture. With tsunami disaster prevention as the main target, we arecollaborating with research institutes and related local governments to develop new disasterprevention information network. We have explored the possibility of transmission, and analyzed thedata obtained from the observation network to find out the possibility of various geophysical events.
Feasibility and optimal configuration for the detection of large-scale geophysical events as well as
human-caused events, or explosions, were studied. The results of this study are presented in theform of an analysis of the environmental noise in the infrasound caused by artificial sources,
vibration sources and weather phenomena. In addition, we will also be able to respond to various
local conditions, including the effects of sensor installation and the surrounding terrain, at theinstallation point. We examined the dependence on environmental factors by using datasets obtainedin a few years.
As for the main target of this research project, tsunami-excited infrasound, studies were reported
after the Great East Japan Earthquake in 2011, but no major tsunami occurred during the period of
this research, so it could not be verified. However, with respect to the infrasound during the passage
of a typhoon that excites the same degree of infrasound are verified for a few cases. Specifically, inTyphoon No. 21, which caused severe damage to the Japanese archipelago on September 4, 2018, thesame kind of large infrasound wave with a period of more than 30 minutes and over-pressure of morethan 100 Pa was clearly observed at Muroto City observation site, where the typhoon hit directly.
Frequency and amplitude of the wave were about the same or greater than that of the tsunami, butthey were detected only at Muroto City observation site; no detection at more distant observation

sites from Aki City, at about 25 km far away from Muroto. The difference between the tsunami andthe typhoon could clearly be seen.
The mechanism for communicating tsunami information is based on a system that theinformation obtained at each observation site is stored on multiple data servers with uploading andaggregating the waveforms, with their quasi-real-time waveform display on web browsers. The
system was developed and opened to the public for some of the observed datasets in Kochi Prefecture.
In addition, a briefing conference was held in Kuroshio Town, Kochi Prefecture, for representativesof the local community in cooperation with local government officials. We exhibited at various
disaster prevention exhibitions to discuss the possibility of linking with existing disaster prevention
information transmission systems with the people concerned. Discussions and specific outcomes
include real-time earthquake alerts that operate a membership-based emergency earthquake early
warning provision service. Infrasound for the preliminary stages of constructing a new system incollaboration with the Real-time Earthquake & Disaster Information Consortium (REIC) ,experiments are underway at some points in the infrasound observation network. Information justbefore the earthquake is obtained in conjunction with the earthquake early warning system, and in
the event of an earthquake, triaxial acceleration (vibration) sensors on the comprehensive
infrasound sensors detect seismic motions at each site, resulting in a double-triggering system,
which turns on the tsunami infrasound standby mode. If the infrasound arrives at the speed of soundand can be verified on site, we can estimate the magnitude of tsunami, i.e. , it can make a positive
contribution to tsunami prevention.