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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 />

JSS002 Oral Presentation 1777<br />

Observations of Seiche at japanese coast in the Japan Sea and the<br />

significance to tsunami amplification<br />

Prof. Kuniaki Abe<br />

dental hygien Niigata Junior College, Nippon Dental University <strong>IASPEI</strong><br />

In situ observations of seiche were conducted at 55 points of bay heads and ports facing to the Japan<br />

Sea in . Sea level was detected with a pressure gauge for 6 hours per point in time interval of 1 minute<br />

and the total data was prepared in the period from November 11, 2002 to December 25, 2006. The<br />

time histories were decomposed into amplitude spectra and the most dominated period component was<br />

identified for each observation point. The result shows that the values vary from 7 to 167 min and level<br />

of 10 minutes occupies 25 % in all the observation points. These periods are approximated to ones of<br />

the fundamental mode under the consideration of the length and the sea depth. Moreover, the<br />

frequently observed periods of 10 to 30 minutes correspond to typical periods of tsunamis which are<br />

excited by large earthquakes, especially in . Therefore, we studied a relation of the dominant period<br />

with one of tsunami in bays and ports. We used tide gauge records of tsunamis observed in the 1993<br />

Hokkaido nanse-oki, the 1983 Nihonkai chubu and the 1964 Niigata Earthquakes. Responses of tide<br />

stations were reduced based on the recovery time obtained by Satake et al.(1988). The amplitude<br />

spectra were calculated for the record of 6 hours from the earthquake origin time with the same<br />

method as for the seiche. Selecting 30 seiches observed at the neighborhoods of the tide stations we<br />

compared the dominant periods with ones of the tsunamis observed at the same bays. Appearance of<br />

the same dominant period between seiche and tsunami at the same bay was counted for all the<br />

observation points in each tsunami. The same period of seiche was defined for the period within the<br />

error of 50 %. The ratios reach to 38, 44 and 8% for 1993, 1983 and 1964 tsunamis, respectively. This<br />

value is an indicator of resonance of tsunami to bay and port. The difference is caused by one of typical<br />

period mainly related to source size and sea depth in the source. In this case sea depth is an important<br />

factor. The typical sea depths are 3000, 2000 and 70 m for 1993, 1983 and 1964 tsunamis, respectively<br />

(Abe, 2007). It is concluded that the difference directly is reflected to one of period and brought the<br />

difference of resonance.<br />

Keywords: seiche, tsunami, dominant period

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