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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 1825
Numerical simulation of tsunamis around Shanghai on the East China Sea
Coast Due To Great Nankai, Japan, earthquakes
Dr. Tomoya Harada
Research Center for Urban Safety and Security Kobe University IASPEI
Katsuhiko Ishibashi
There has been a controversy among Japanese scientists whether Chinas Shanghai and its vicinity on
the East China Sea coast were struck by large tsunamis or not due to the great interplate Nankai
earthquakes along the Pacific coast of southwest Japan. Chinese historical documents report remarkable
water disturbances in rivers, canals, ponds and wells around Shanghai in 1498, 1707 and 1854. The
dates in 1707 and 1854 coincide with those of the Nankai earthquakes and the date in 1498, with that
of a large earthquake in southwest Japan. Tsuji and Ueda (1997) claimed that these water disturbances
meant large tsunamis and that the 1498 earthquake had also been the Nankai earthquake. Utsu (1988)
and Ishibashi (1998), on the contrary, considered the water disturbances not to be tsunamis but seiches
caused by long-period seismic waves. In this study, in order to terminate this controversy, we carried
out the numerical simulation of tsunami propagation in the East China Sea for the 1707 Hoei, the 1854
Ansei and the 1946 Showa Nankai earthquakes, though the computation was the first-order
approximation. We assumed six static fault models of the 1707, 1854 and 1946 earthquakes proposed
by Ando (1975, 1982) and Aida (1979, 1981a, b). Tsunami propagations were computed by the finitedifference
method for the liner long-wave equations in the area of 120-140E and 2036N using 1-minute
bathymetry data provided by GEBCO. The time step of the computation is 3.0 sec to satisfy a stability
condition of the grid system. The friction with Mannings roughness coefficient of 0.03 is provided at the
ocean bottom where the water depth is shallower than 100m. Initial conditions of tsunami propagation
are ocean bottom deformation due to earthquake faulting, which were computed by Okadas (1985)
program. Concerning boundary conditions, the total reflection on the coast and open boundary to
outside the computational area were used. As the results, tsunamis caused by great Nankai earthquakes
propagate into the East China Sea mainly through the Tokara strait, and they reach the coast around
Shanghai about nine hours after the earthquake occurrence. The tsunami height on the China coast is
not large, less than 1 meter, even for presumably overestimated fault slip of the 1707 Hoei Nankai
earthquake model. Thus, water disturbances recorded in China are considered not to be tsunamis but
effects of seismic waves. However, it should be noted that tsunami and seismic effect due to the next
Nankai earthquake, which is anticipated to recur around the middle of this century, may affect to
considerable extent to the modernized society of China. We thank Yuichiro Tanioka for providing us his
tsunami computation program.
Keywords: tsunami simulation, east china sea, great nankai earthquake