IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS002 Poster presentation 1799
Tsunami waveform analysis for historical large tsunamis generated by the
large earthquakes along the Kurile trench
Prof. Yuichiro Tanioka
Institute of Seismology and Volanology Associate Professor IASPEI
Kenji Satake, Paula Dunbar
Many large earthquakes have occurred along the Kurile trench due to subduction of the Pacific plate
beneath the Kurile Islands, and large tsunamis have been generated by those earthquakes. The large
earthquakes occurred in this region in the late 19 century or in the early 20 century are not well studied
because of lack of seismological data. However, tsunami waveform data observed at tide gauges around
the Pacific Ocean are available for some of those historical earthquakes. In this paper, we analyze the
observed tsunami waveforms to study the source processes of those historical large earthquakes,
especially the 1894 Nemuro-oki and 1918 Kurile earthquakes. The fault model of the 1894 Nemuro-oki
earthquake is estimated using the observed tsunami waveform at Ayukawa in Sanriku, Japan. The most
recent large earthquake in this area is the 1973 Nemuro-oki earthquake. The source model of the 1894
earthquake has to be compared with that of the 1973 Nemuro-oki earthquake. The tsunami numerical
computation is carried out using the finite different approximation of the linear long-wave equations. By
comparing the observed and computed tsunami wavefroms, we conclude that the fault length of the
1894 Nemuro-oki earthquake is approximately 200 km, much larger than that of the 1973 Nemuro-oki
earthquake, 40-80 km. The slip amount is estimated to be 2.4 m by comparison of observed and
computed amplitudes between the largest peak and the first trough. The total seismic moment of the
1894 Nemuro-oki earthquake is 2.9 x 10**21 Nm (Mw8.3) by assuming the rigidity of 6 x
10**10N/m**2. This estimate is much larger than the estimated seismic moment of the 1973 Nemurooki
earthquake. The 1918 large Kurile earthquake occurred off the central Kurile Islands. The epicenter
of this earthquake is located at southwest of the source areas of the recent 2006 and 2007 large Kurile
earthquakes. The tsunami waveforms for the 1918 earthquake are observed at three tide gauges in
Japan, Kushiro, Choshi, and Chichijima. The tsunami waveforms are also observed at tide gauges in
Honolulu, Hawaii, and in San Francisco. Those tsunami data are collected to analyze the source process
of the earthquake.
Keywords: tsunamis, kurile, tide gauge data