日本地球惑星科学連合2018年大会

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[EJ] Eveningポスター発表

セッション記号 S (固体地球科学) » S-SS 地震学

[S-SS08] 活断層と古地震

2018年5月22日(火) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:小荒井 衛(茨城大学理学部理学科地球環境科学コース)、近藤 久雄(産業技術総合研究所 活断層・火山研究部門)、道家 涼介(神奈川県温泉地学研究所、共同)、松多 信尚(岡山大学大学院教育学研究科)

[SSS08-P12] Paleoearthquakes recorded in the Fuji Five Lakes during the last ca. 6000 years (Fuji Five Lakes, Japan)

Laura Lamair1、*Aurelia Dominique Hubert-Ferrari1Shinya Yamamoto2Yusuke Yokoyama3Yosuke Miyairi3Ed Garrett6Osamu Fujiwara7Stephen Obrochta8Atsunori Nakamura7Marc De Batist4Vanessa M.A. Heyvaert5QuakeRecNankai Team4 (1.University of Liege, Department of Geography、2.Mount Fuji Research Institute, Yamanashi Prefectural Government, Yamanashi, Japan、3.University of Tokyo, Atmosphere and Ocean Research Institute, Chiba, Japan、4.Ghent University, Department of Geology, Ghent, Belgium、5.Geological Survey of Belgium, Royal Belgian Institute of Natural Sciences, Brussels, Belgium、6.Durham University, Department of Geography, Durham, UK、7.National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan、8.Akita University)

キーワード:Seismo-Turbidites

In Japan, one pioneering lacustrine paleoseismological study was conducted in Lake Biwa in the 1990s. However, despite the high seismicity of Japan, the field of lacustrine paleoseismology did not expand. Paleoseismological studies were more focused on inland trenches and coastal records. The paleoseismological data obtained by that way covers the last ~6000 years but contains hiatuses. Using lacustrine sediment allows us to span the same time period and to have a continuous record. Here, we present the second lacustrine paleoseismological study conducted in Japan.

The Fuji Five Lakes are situated close to the triple junction, where the North American Plate, the Eurasian plate and the Philippine Sea Plate meet. Therefore, the region can be impacted by megathrust earthquakes generated along the Nankai-Suruga and the Sagami subduction zones. In addition, intraplate earthquake may affect the Fuji Five Lakes region. In the framework of the QuakeRecNankai project, we investigated two of the Fuji Five Lakes, Lake Motosu and Lake Sai.
Here, we present the paleoseismological record of Lake Motosu and Lake Sai over the last 6000 and 2000 years, respectively. The turbidites were identified based on geophysical (magnetic susceptibility, grainsize) and geochemical properties (XRD, XRF) as well as SEM analysis. The turbidites were dated by 210Pb/137Cs, 14C dating and correlated with historical earthquakes. For prehistorical earthquakes (i.e., before the 6th century), they were correlated with geological evidences recorded along the Eastern Honshu coastline (i.e., tsunami deposits, coastal uplift, emerged ridge beaches). Over the last 6000 years, seismo-turbidites occurred with a mean recurrence time of 184±8 years. The near absence of large mass-transport deposits in the last 6000 years suggest that earthquake shaking mostly induced the remobilization of thin veneers of sediments in Lake Motosu. In Lake Sai, the earthquake fingerprint differs from Lake Motosu. Over the last 1200 years, past earthquake shaking induced turbidites, delta collapse and liquefaction (sediment volcanoes).