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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy<br />

(S) - <strong>IASPEI</strong> - International Association of Seismology and Physics of the Earth's<br />

Interior<br />

JSS003 Poster presentation 1883<br />

Can the offshore pressure sensors contribute to early tsunami warning<br />

system<br />

Dr. Hiroyuki Matsumoto<br />

Deep Sea Research Department JAMSTEC <strong>IASPEI</strong><br />

Hitoshi Mikada, Kenichi Asakawa, Katsuyoshi Kawaguchi<br />

Early tsunami warning system is necessary, in particular for those regions that have historically never<br />

experienced devastating tsunami disasters, such as the 2004 Indian Ocean tsunami disaster. In Japan,<br />

seven permanent offshore cabled observatories, in which bottom pressure sensors are included have<br />

been operated by various research institutions and universities since 1970s. Two case studies of early<br />

tsunami detection by the bottom pressure sensors are introduced together with demonstrating by the<br />

tsunami computation; one is by the off Kii-peninula, Japan earthquake (M7.4) in 2004 and the other is<br />

by the Kuril Islands earthquake (M8.3) in 2006. Water pressure fluctuations during the 2004 off Kiipeninsua<br />

earthquake was successfully obtained by the offshore cabled observatory off Muroto, SW<br />

Japan, approximately 200 km west of the earthquake epicenter, i.e, the tsunami source, and the<br />

tsunami signals were processed from the acquired dataset after applying moving average filtering. As a<br />

result, two pressure sensors could detect the tsunami signals 20 minutes before the first tsunami arrival<br />

at Muroto, the nearest coast to the observatory. Tsunami amplitude observed by the pressure sensors<br />

was less than 0.1 m, while that observed at the coast was 0.5 to 1 m. On the other hand, the tsunami<br />

from the mega-thrust earthquake taken place off Kuril Islands on 15 November 2006 was also observed<br />

by the other offshore cabled observatory off Kushiro, NE Japan, 800 km away from the epicenter.<br />

Although most of the tsunami energy propagated toward off the Pacific Ocean, about one hour later,<br />

the series of the tsunami signals was observed by three bottom pressure sensors. The tsunami<br />

amplitude was approximately 5 cm, whereas that observed at the coast were a few tens of centimeters.<br />

In case of the Kuril Islands earthquake, the tsunami could be detected 20 min earlier than that arrived<br />

at the eastern tip of Japan. This means that the offshore observatory off Kushiro possibly become the<br />

most rapid warning strategy against tsunamis generated along the Kuril trench. Our recent experiences<br />

of tsunami observation suggest that the bottom pressure sensors make us possible to detect tsunami<br />

itself in advance. From a viewpoint of early tsunami warning or forecasting, the bottom pressure<br />

sensors would surely have a potential use for future regional tsunami disaster mitigation.<br />

Keywords: tsunami, warning system, offshore observatory

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