Vol.2 No.2 2009

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Research paper : A study of paleoearthquakes at archeological sites (A. Sangawa)−91−Synthesiology - English edition Vol.2 No.2 (2009) time, I felt strongly that if the knowledge of earthquakes known to researchers were widely known to the general public, perhaps the damages might have been decreased.According to the timetable (Fig. 5) compiled from the written records and earthquake trace materials for the great earthquakes from the Nankai Trough, it is almost inevitable that a Nankai and Tokai (Tonankai) earthquakes will occur in the middle of the 21st century. Moreover, it is highly likely that these great earthquakes will occur simultaneously or sequentially. In addition, there is a period of increased earthquakes (active period) several decades prior to the Nankai earthquake, and it is believed that the active period started after the Hanshin Awaji Earthquake[25].In the new century, measures against earthquakes are becoming important, and both research institutes and governments are working on them. I think it is particularly effective to utilize the earthquake traces in archaeological sites to diffuse the knowledge to the general public.As an example, I shall mention the Takamatsuzuka Tomb in Asuka, south of Nara. In 1972, the colorful wall paintings of the beauties of Asuka Period were found in the stone chamber of this tomb, and public interest in archaeology increased. In the recent survey, many fissures were found in the mound of the Takamatsuzuka Tomb, and some fissures reached the stone chamber[26]. These were caused by the great earthquakes that occurred repeatedly at the Nankai Trough. In 2006, the stone chamber was disassembled to prevent the deterioration of the wall paintings, and the results of the excavation done at the time were covered widely by the newspapers and television. In addition, traces of the earthquake that damaged the Takamatsuzuka Tomb was reported, and many people learned that “ great earthquakes of the Nankai Trough is approaching, and a broad area including Asuka will be shaken.”The general public holds the impression that the mechanism of earthquakes is difficult to understand. However, by looking at the earthquake traces at the archaeological site, they can easily understand that in the past, a great earthquake struck the area they reside and left markings. When an archaeological excavation is done, public viewings are held, and in some cases tens of thousands of people visit the site. Since the establishment of earthquake archaeology, earthquake traces have also become subjects of viewing and are reported each time by the media. Their effectiveness as educational tools is great.I have several opportunities to talk about earthquakes to the general public at lectures and events. On such occasions, referring to archaeological sites and history eases diffusion of knowledge to people who are not particularly interested in earthquakes. Recently, there are increased opportunities for earthquake education to elementary school students, and using earthquake traces of well-known archaeological sites improves educational value.About 20 years have passed since I started this study, and the awareness to take up earthquake traces found at archaeological surveys as subjects of research has diffused widely among archaeologists, along with basic survey methods. In this sense, my initial objective has been achieved. I have written books for the general public on this subject. Particularly, in the book published in 1992[13], I described the research results and survey methods of the earthquake traces in archaeological sites, and many readers adopted interest in earthquake archaeology. I also introduced the history of earthquakes in Japan since the Jomon Period[16].The consciousness that archaeological sites, which may seem unrelated, may become subjects of research has spread to researchers of various earthquake-related fields such as geology and engineering, and research from new perspectives are being started.I worked as visiting professor at the Institute of Industrial Sciences, the University of Tokyo, as well as at the Disaster Prevention Research Institute, Kyoto University, and am conducting research in collaboration with researchers of earthquake engineering and geotechnical engineering.As one example, as in the aforementioned Hariehama Site, at the Motojima Site of Shizuoka Prefecture, traces where only sand rose out from the gravel layer in liquefaction were observed[27]. Various other findings on liquefaction obtained from the sites are becoming widely known among engineering researchers[28].Also, in the Imashirozuka Tomb where the sliding and moving of the soil of the mound in a landslide could be observed sequentially, joint research including mathematical analysis was conducted[29]. Also, traces of landslide and fissures are being studied with engineers at the Nishimotomezuka Tomb and Takamatsuzuka Tomb[30]-[32].In the future, I hope studies using archaeological sites will progress further, and I shall continue to work on the diffusion of this knowledge.References[1][2]Research Group for Active Faults of Japan (ed.): Nihon No Katsudanso Bumpuzu To Shiryo (Active Faults in Japan,Sheet Maps and Inventories), University of Tokyo Press, Tokyo (1980) (in Japanese).Geological Survey of Japan, Agency of Industrial Science and Technology, Ministry of International Trade and Industry (ed.): 1:500,000 Neotectonic Maps Series (1982-87) (in Japanese).

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