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Journal of Japan Association for Earthquake Engineering
Vol. 7 (2007) No. 2 P 160-179



Mudflow type failure with gentle slope occurred at Dateshita in Tsukidate town during the 2003 Sanriku-Minami earthquake in Japan. The fluid soil was consisted pyroclastic sediment material which classified as a volcanic sandy soil with pumice. This failure phenomenon was due to loose volcanic sandy soil material with fluidization type flow by the trigger of strong ground motion of the earthquake, against of its material unsaturated condition. Unfortunately, when the main shock occurred, strong ground motion record was failed to observe at Tsukidate K-NET station, the closest observatory to Dateshita landside site. Therefore, we conducted to estimate strong ground motion seismograms at mudflow failure site, because of few study regarding the relationship between ground motion records and mudflow type failure consisted of unsaturated volcanic sandy soils. We estimated strong ground motion waveforms using empirical Green's function method using two after shocks comparing several seismic intensities surrounding the Tsukidate town. Therefore, we recognized both dissipation energy, one is computed by 1-D geotechnical response analysis and the other one is obtained by conducting laboratory testing, would be good relationship, then, we proposed new method for estimating liquefaction potential of unsaturated pyroclastic material. We finally realized mudflow type failure with gentle slope at Tukidate town is due to fluidization and liquefaction type soil collapse by the trigger of strong ground motion.

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