An empirical study of sediment disasters subsequent to earthquake damages

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This study consists of two parts that the research for subsequent sediment disasters after the Chi-chi earthquake in Taiwan 1999, and the research for the debris flows in Fujiwara town in Mie prefecture subsequent to an earthquake.1. Research in Taiwana). Geomorphological change in slope failures after earthquakeTo clarify the change of property and form of the slope failure induced by the Chi-chi earthquake, we conduct the basic on site research in two typical damaged areas. In Chu-fen-erh-shan area, we found the spillway from the landslide dam was eroded and some check dams in the stream damaged seriously. In Tsaoling area, we illustrated the 20-meter fallback at the cliff top, which made by the Chi-chi earthquake. And we continued the seismic exploration on site in order to clarify the degradation of ground property after earthquake.b). Typhoon impact after the earthquakeAfter the typhoon impact in the summer of 2004 in Taiwan, sediment disasters on mountainous slope expanded to the northern area of the damaged area by Chi-chi earthquake in 1999. We surveyed in the middle stream of Tachiachi river, and found the typical pattern of a disaster expansion that a debris flow occurs first, after that the main stream is fed by the sediment from tributaries, then the riverbed raises, the flood disaster occurs at last.2. Debris flows research in Fujiwara town in Mie prefectureSeveral debris flows occurred in Fujiwara town subsequent to an earthquake but the causal relationship is not clear. We clarified the main factor for recurrences of debris flows in Fujiwara town were the resumed flow of the sediment in riverbed supplied from upstream and eroded riverbank through the field research. Also, we found that a recurrence of debris flows can be predictable using 10 minutes rainfall data.