Vol.2 No.2 2009

8/98

Research paper : A study of paleoearthquakes at archeological sites (A. Sangawa)−88−Synthesiology - English edition Vol.2 No.2 (2009) earthquakes were reported in the sites around Kurume City, Fukuoka Prefecture, including the archaeological site of the ancient Tsukushi Capital. Their dates were limited to the late 7th century, and this corresponded with the Tsukushi Earthquake described in the Nihonshoki. In 1992, a trace of fault activity during this period was found in the survey of Maekawa Maeda Site located right on top of the Minou Fault Zone that runs east-west along the east of Kurume City. Thus, it was verified that a great earthquake occurred due to the activities of Minou Fault Zone in 679, and this event was recorded in the Nihonshoki.Also, in the Nihonshoki, the earthquake of 684 (13th Year of the Reign of Emperor Tenmu) is described in details: “Great earthquake occurred at around 10 o’clock at night, and men and women throughout the country screamed and ran. Mountains collapsed and rivers flooded. Government buildings, people’s houses, warehouses, temples, and shrines in the provinces were damaged, and many people and cattle were injured or died. The hot springs of Dogo Spa of Iyo stopped. In the province of Tosa (Kochi Prefecture), about 500,000 shiro or 1,000 choho (about 10 km2) of farmland submerged and became ocean. Waves rushed to the shores and ships for carrying tributes were swept away.”Severe tremors in a wide area including Kinai, stopping of the hot springs of the Dogo Spa, submersion of Kochi Plain, and tsunami along the Pacific coast are characteristics of the Nankai earthquake that occurs at the “Nankai Trough” which is on the plate boundary of the Pacific Ocean bottom. Therefore, it can be seen that a Nankai earthquake occurred in 684.5.3 Great earthquakes in the Nankai TroughFigure 5 shows the timetable of mega-earthquakes in the Nankai Trough. The Trough is divided into 5 segments, A~E. A to B cause the Nankai earthquake, and C to E cause the Tokai earthquake. After the Showa Period, the latter is divided into C and D for Tonankai earthquake and E for postulated Tokai earthquake. In Fig. 5, the western calendar years are dates of occurrences that can be determined from written records such as the Nankai earthquake of 684.After the Edo Period where there are abundant historical materials, most major earthquakes were recorded in writing. In contrast, the absolute quantity of historical materials decreases significantly before the Edo Period, and records may not exist for earthquake occurrences. This is the reason the number of earthquakes after the Edo Period increases in the western calendar timetable in Fig. 5.In the survey of Sakajiri Site in Fukuroi City located east of Lake Hamana, Shizuoka Prefecture, the residential remains from the mid 7th century were torn by many sand boils. Since government buildings were built in early 8th century on top of the sand boil, it could be seen that the Tokai region was severely shaken in the late 7th century. Moreover, traces of liquefaction in the same period were discovered in the Kawai Site in Shizuoka City and the Tadokoro Site of Aichi Prefecture. Therefore, there is high possibility that a Tokai earthquake occurred at the same time as the Nankai earthquake of 684 described in the Nihonshoki. For the Nankai earthquake of 684, corresponding earthquake traces 123456ABCDE0200 kmABCDE194618541605170713611944185416051707149888710961099684234561Tokai earthquakeTonankai earthquakeTokai earthquakeNankai earthquakeNankai TroughFig. 5 Timetable for great earthquakes of the Nankai Trough (additions to Reference[13]).The years shown in Western calendar years are occurrences of earthquakes known from written record. represent sites from which earthquake traces were found.1. Azono Site. 2. Kawanabe Site. 3. Sakafuneishi Site. 4. Tadokoro Site. 5. Sakajiri Site. 6. Kawai Site.020 kmSFOFHFKFNF54123RFZAFZYamatogawaYodogawaNaraKyotoActive faultOsakaSakaiAwajishimaFig. 6 Traces of earthquake that are thought to be left by the Fushimi Earthquake (additions to Reference[16]). represent the sites from which traces of the Fushimi Earthquake were found.1. Kizugawa Riverbed Site. 2. Uchisato Haccho Site. 3. Imashirozuka Tomb. 4. Sumiyoshi Miyamachi Site. 5. Nishimotomezuka Tomb.The fault that was active in the Great Hanshin Awaji Earthquake of 1995: NF Nojima Fault. Ones that were active in the Fushimi Earthquake of 1596: AFZ Arima-Takatsuki Fault Zone, HF Higashiura Fault, OF Nodao Fault, and SF Senzan Fault.Ones that are speculated to have been active in the Fushimi Earthquake: RFS Rokko Fault Zone and KF Kusumoto Fault.

※このページを正しく表示するにはFlashPlayer9以上が必要です