Source Fault Model of the 1771 Yaeyama Tsunami, Southern Ryukyu Islands, Japan, Inferred from Numerical Simulation |
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Authors: | Mamoru Nakamura |
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Institution: | (1) Faculty of Science, University of the Ryukyus, Senbaru 1, Nishihara-cho, Okinawa 9030213, Japan |
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Abstract: | The 1771 Yaeyama tsunami is successfully reproduced using a simple faulting model without submarine landslide. The Yaeyama
tsunami (M 7.4), which struck the southern Ryukyu Islands of Japan, produced unusually high tsunami amplitudes on the southeastern
coast of Ishigaki Island and caused significant damage, including 12,000 casualties. Previous tsunami source models for this
event have included both seismological faults and submarine landslides. However, no evidence of landslides in the source has
been obtained, despite marine surveying of the area. The seismological fault model proposed in this study, describing a fault
to the east of Ishigaki Island, successfully reproduces the distribution of tsunami runup on the southern coast of the Ryukyu
Islands. The unusual runup heights are found through the numerical simulation attributable to a concentration of tsunami energy
toward the southeastern coast of Ishigaki Island by the effect of the shelf to the east. Thus, the unusual runup heights observed
on the southeastern coast of Ishigaki Island can be adequately explained by a seismological fault model with wave-ray bending
on the adjacent shelf. |
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Keywords: | The 1771 Yaeyama tsunami Ryukyu Islands tsunami generation |
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