No. 3, p , 2003 Tsunami traces in the 17th century and evaluations of their inundation limits from distribution of event deposits along the so

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1 No. 3, p , 3 Tsunami traces in the 17th century and evaluations of their inundation limits from distribution of event deposits along the southern Tokachi coasts, eastern Hokkaido, northern Japan Futoshi Nanayama 1, Kiyoyuki Shigeno, Yuji Soeda 3, Ryuta Furukawa, Hisayo Okahashi 5, Kenichi Saito, Yoshiharu Yokoyama 7, Kenji Satake and Mitsuru Nakagawa 9 1 Institute for Marine Resources and Environment, GSJ/AIST, nanayama-f@aist.go.jp Meiji Consultant Co., Ltd., shigeno-k@meicon.co.jp 3 Historical museum of Hokkaido, soeda@jg.so-net.ne.jp Institute of Geosciences, GSJ/AIST, 5 Graduate School of Science, Osaka City University, hisayo@sci.osaka-cu.ac.jp Tsukuba University, saiken@erc.suiri.tsukuba.ac.jp 7 Graduate School of Science and Engineering, Waseda University, yokoyama-y@ruri.waseda.jp Active Fault Research Center, GSJ/AIST, kenji.satake@aist.go.jp 9 Hokkaido Branch, GSJ/AIST, nakagawa.gsj@aist.go.jp Abstract: Large earthquakes along the Kuril subduction zone have caused tsunami damage on the Pacific coast of eastern Hokkaido, between Nemuro and Tokachi. We have previously reported 15 layers of tsunami deposits in peat beds and layers of tsunami deposits in lacustrine sediments between Nemuro and northern Tokachi. In this study, we report tsunami deposits from the southern part of Tokachi coast between Taiki and Hiroo Towns. We studied terrace deposits along the Pacific coast between Hiroo and Taiki and lacustrine deposits in Lake Horokayanto. At these sties, we identified only one layer, which we correlate to (17th century tsunami deposit) based on two key tephra layers named Ta-b (17) and (13). We estimated the inundation distances of 15-7 m on the terrace area and 1- m in Lake Horokayanto. The sedimentary structures of on the terrace show inverse grading, and we interpreted that these sediments were transported by traction currents such as a high-density turbidity current. However, we could not find other deposits such as Ts1 formed by 195 Tokachi-oki tsunami (Mt.) or 19 Chilean tsunami (M 9.5), Ts by 13 Tokachi-oki tsunami (Mt.) and older event deposits (Ts~) in this area. Keywords: tsunami, event deposit, inundation limit, Kuril subduction zone, eastern Hokkaido, southern part of Tokachi coast, terrace deposit Fig , 1a, b a, b 15 5 b; Nanayama et al., 3 13 Ts1 Ts Ts 13 97

2 1c Fig. 1 Fig. 1 a, b 1 3 b 13 Fig. 1 1:5, pp, 1999 cm SPAD-53. cm 7 cc pp m MS- Magnetic Susceptibility System (Bartington ) 5cm 5cm 1cm X.g 3.g 15% ~ Mt m 19 M m 9m 191.m a, b 1999 Fig. 1 9

3 17 3m Fig. c, d Ta-c.5 ka a 3 5m 1 3m.5m Fig. c 3 9m 15 3cm 15 cm Fig. c 5 Ba 9 13m 3m Bs 11m m Ks 13 15m 15m Ah 9m 7m Mb 9 13m 7m Figs. and 3.5km.5 km 1.9 km Fig. m 3.m 199 Fig. 7m 199 Fig. a 19 washover fan: Shepard, 1973 Fig. b 1 Ho Fig. Ba pp Fig. N/-3/ Ba cm 1 7.5YR/ 7.5YR/ Ta-b Fig. 5 Ba-1 cm Ba-1.5cm Fig. 5 99

4 Fig m Fig. 5 Bs pp 3 Fig. Bs-1 3cm Ta-b 1 Fig. 5 Bs-1 5cm 159.7m Fig. 5 Ks pp 3 Ks-1 15 cm 1 Fig. Ks-1 3cm Ks-1 N W a Ks-1 13 cm Ks-.5cm Ks-3 Ks- Ks-3 Fig. 15.3m Fig. Ah pp 5 Fig. 3 Ah-1 1 cm 1 Fig. 7 Ah-1 5cm Ah-3 Ah- 1.5cm.m Fig. 7 pp Fig. 3 Mb cm 1 Fig. Mb Mb-1 3.5cm 7.5cm N W Mb 1 cm Fig. 3

5 m Ho 5 Fig. Y3/1-/1 Potamocorbula amurensis Corbicula japonica Ammonia beccarii, Buccella frigida Ho cm 1 Fig. N/-3/ Ho- Ho-5 Fig. Ho Ho-5 1m m Fig. Ho-1, Ho- Fig. Ho-1 1b Fig. Ho-1, Ho- Ah Ah-1~ X Ah-1 Fig. 9 X Ah-1 Ah- Ah-3 Ah- cm Ah-1 3 Fig. 9 (1) () g/ (3) 3g/ Ah Ah1 Ba Ba1 Ta-b cm cm Ah Pinnularia borealis Hantzschia amphioxys Luticola mutica 93% 31

6 Thalassiosira eccentrica Thalassiosira sp., Coscinodiscus marginatus 7% Ah-1 Ah- Ah-1 3 Thalassiosira sp. 1% Ba Ba-1 Ta-b Pinnularia borealis Hantzschia amphioxys Luticola mutica % Eunotia Pinnularia % 1% Thalassiosira eccentrica, Thalassiosira sp., Coscinodiscus marginatus Hyalodiscus sp. % Ba Ta-b Pinnularia borealis Hantzschia amphioxys Luticola mutica % 9% Thalassiosira sp. % Ba- Thalassiosira sp. 1% Ah, Ba % 1 Ta-b b 17 b RT1 TT1 a 111 b RT, RT1, RT-, RT-3, RT-, RT-5 1~m 3m Ts Ts5, Ts b Bs-1 Dobkins and Folk, 197 3

7 17 b a 3g/ 3 g/ a Bagnold, 195 Lowe, 19 1 m 15m 15 7m 3 bed load wash load 15m 17 15m 15m 15m 1 1 Ta-b m 15m 15 7m 33

8 m 15m Bagnold, R.A. (195) Experments on a gravity-free dispersion of large solid spheres in a Newtonian fluid under shear. Proc. Roy. Soc. London (A), 5, 9-3. Dobkins, Jr., J.E. and Folk, R.L. (197) Shape development on Tahiti-Nui. Jour. Sed. Petrol.,, , , 59, , -9 1, No.,, i-ii a, No. 31, 9-9 b, No., , 7, , No. 53, A ,, 397p. Lowe, R. D. (19) Sediment gravity flows: II. Depositional models with special reference to the deposits of high-density turbidity currents. Jour. Sed. Petrol., 5, , No. 3, 9- a No. 9- b, No., a, No. 1, 37-1b 9, No. 1, 33-9, No., , No. 15, , No. 5, 1-1c, No. 1, 51-7 Nanayama, F., K. Satake, R. Furukawa, K. Shimokawa, B.F. Atwater, K. Shigeno and S. Yamaki (3), Unusually large earthquakes inferred from tsunami deposits along the Kuril trench. Nature,, 3

9 , , No. 5, , No. 9, p. Shapard, F.P. (1973) Submaine Geology, 3 rd ed. Harper and Row, New York, 517 p

七山太重野聖之添田雄二古川竜太岡橋久世斎藤健一横山芳春佐竹健治中川充 N N N N Honshu Hokkaido Sakhalin Study Area Mt. 195 19 Mt. 15 Mt 7. Kuril Islands Mt. 199 Mt.1 193 Mt. 19 Mt. 13 Mt.

5 Kuril Trench N Tokochi-otsu Lake Chobushi Lake Yudo-numa Lake Oikamanai Lake Horokayanto Fig. Bansei-onsen Hidaka Mountains Taiki Toberi Marsh Hamataiki Fig.

10 七山太重野聖之添田雄二古川竜太岡橋久世斎藤健一横山芳春佐竹健治中川充 N N N N Honshu Hokkaido Sakhalin Study Area Mt Mt. 15 Mt 7. Kuril Islands Mt. 199 Mt Mt. 19 Mt. 13 Mt. cm/yr Pacific Plate Mt E 1 E 1 E 1 E 1 E 1 E 15 E 15 E Mt.5 Kuril Trench N Tokochi-otsu Lake Chobushi Lake Yudo-numa Lake Oikamanai Lake Horokayanto Fig. Bansei-onsen Hidaka Mountains Taiki Toberi Marsh Hamataiki Fig. 3a Rekifune River Asahihama Fig. 3b Toyoni River 第 1 図. 千島海溝のテクトニクス, 海溝型地震の余震域 ( 上 ) と十勝海岸の調査地域位置図. Fig. 1. Tectonic map around Hokkaido showing earthquake sources of the Kuril subduction zone (above) and index map of the study areas (below). Hiroo Pacific Ocean m 3

北海道東部, 十勝海岸南部地域における 17 世紀の津波痕跡とその遡上規模の評価 N Lake Oikomanai Lake Horokayanto Ho-5 Distribution area of Ho- Ho-3 Ho- Ho-1 Ba- Ba-3 Ba- Ba-1 Line Ba Bansei-onsen Line Ho Toberi Marsh Inundation limit

11 北海道東部, 十勝海岸南部地域における 17 世紀の津波痕跡とその遡上規模の評価 N Lake Oikomanai Lake Horokayanto Ho-5 Distribution area of Ho- Ho-3 Ho- Ho-1 Ba- Ba-3 Ba- Ba-1 Line Ba Bansei-onsen Line Ho Toberi Marsh Inundation limit line of anual storms Bs-3 Bs- Bs-1 Line Bs Legend no tsunami deposits m 第図. 大樹町, 晩成温泉地域 (Ba), ホロカヤントー沼地域 (Ho) および美成地域 (Bs) の各調査測線と今回の調査で明らかとなったイベント堆積物の分布範囲. 国土地理院発刊の 1:,5 地形図晩成および浜大樹を基図として使用. Fig.. Survey lines Ba, Ho and Bs and coring sites and inferred distribution limits of in Taiki Town. 37

大樹町 ~ 広尾町, 更生地域 (Ks), 旭浜地域 (Ah) および小紋別地域 (Mb) の各調査測線と今回の調査で明らかとなったイベント堆積物の分布範囲.

12 七山太重野聖之添田雄二古川竜太岡橋久世斎藤健一横山芳春佐竹健治中川充 N Distribution area of Hamataiki N Lne Ks Distribution area of Line Ah a Line Mb Asahihama Inundation limit line of anual storms b Legend no tsunami deposits m 第 3 図. 大樹町 ~ 広尾町, 更生地域 (Ks), 旭浜地域 (Ah) および小紋別地域 (Mb) の各調査測線と今回の調査で明らかとなったイベント堆積物の分布範囲. 国土地理院発刊の 1:,5 地形図浜大樹および豊似を基図として使用. Fig. 3. Survey lines Ks, Ah and Mb and coring sites and inferred distribution limits of between Taiki and HirooTowns. 3

北海道東部, 十勝海岸南部地域における 17 世紀の津波痕跡とその遡上規模の評価 a b c d

(a) shoreline area of line Ba, (b) small

13 北海道東部, 十勝海岸南部地域における 17 世紀の津波痕跡とその遡上規模の評価 a b c d Ta-b current direction by gravel fabric N e 第図. 調査地域の野外写真.(a)Ba 測線付近の海浜の状況,(b)Ho 測線で見られる越流によって生じたウオッシュバーファンの産状, (c,d) 海食崖と歴舟川起源の礫層 ( 最終氷期 ) の産状, および (e)as 測線のファブリックを示すイベント堆積物の産状. Fig.. Photographs shownig field occurences. (a) shoreline area of line Ba, (b) small washover fans at line Ho, (c & d) ocurrences of coastal cliffs and their gravel beds of Rekifune River during LGS, and (e) an event deposit with gravel fabric at line As. 39

14 七山太重野聖之添田雄二古川竜太岡橋久世斎藤健一横山芳春佐竹健治中川充 Ba-1 1.m Ba-.m Ba-3 9.3m Bs-1 5.3m Bs- 133.m Bs m 3 5 Ta-b 3 5 Ta-b Ta-b event upflow directions Line Ba Line Bs deposit return flow directions silt Altitude (m) Thickness of event deposits (cm) Altitude (m) Thickness of event deposits (cm) surface sample surface sample Distance from shorline (m) Distance from shorline (m) core number distance from shoreline (m) soils tephra 第 5 図.Ba 測線および Bs 測線の現地形ならびに現汀線からの距離とイベント堆積物の層厚との対応 ( 上 ), および堆積柱状対比図 ( 下 ). Fig. 5. Sedimentary columns and stratigraphic correlation of Lines Ba and Bs. Correlation of thickness of event deposits with topographic profile (avobe) and distance from present shoreline along the two survey lines (below). 3

15 北海道東部, 十勝海岸南部地域における 17 世紀の津波痕跡とその遡上規模の評価 Distance from shorline (m) Distance from shorline (m) Ks-1 9.3m Ks- 1.m Ks m Mb-1 99.m m Mb-.3m Mb- 95.3m core number distance from shoreline (m) 3 3 Ta-b 5 soils tephra event deposit silt 5 upflow directions return flow directions Line Ks Line Mb Ta-b Altitude (m) Thickness of event deposits (cm) Altitude (m) Thickness of event deposits (cm) surface sample surface sample 第図.Ks 測線および Mb 測線の現地形ならびに現汀線からの距離とイベント堆積物の層厚との対応 ( 上 ), および堆積柱状対比図 ( 下 ). Fig.. Sedimentary columns and stratigraphic correlation of Lines Ks and Mb. Correlation of thickness of event deposits with topographic profile (above) and distance from present shoreline along the two survey lines (below). 311

16 七山太重野聖之添田雄二古川竜太岡橋久世斎藤健一横山芳春佐竹健治中川充 1 Altitude (m) 1 1 surface sample Thichness of an event deposit (m) Distance from the shoreline (m) Seaward Landward Ah-1 3.m Ah- 1.9m Ah m Ah-.m 3 5 core number distance from shoreline (m) soil tephra event deposit 第 7 図.Ah 測線の現地形ならびに現汀線からの距離とイベント堆積物の層厚との対応 ( 上 ), および堆積柱状対比図 ( 下 ). Fig. 7. Sedimentary columns and stratigraphic correlation of Line Ah. Correlation of thickness of event deposits with topographic profile (above) and distance from present shoreline along the survey line (below). 31

17 北海道東部, 十勝海岸南部地域における 17 世紀の津波痕跡とその遡上規模の評価 5 Altitude (m) mean water level landward limit surface sample 15 5 Thickness of an event deposit (m) Distance from the shoreline (m) Seaward Ho-1 3.m Ho-.m Ho-3 5.m Ho-.m Landward Ho-5 1.m Ta-b(17) core number distance from shoreline (m) 1 lacustrine silt 13 tephra 1 15 event deposit 1 17 第図. ホロカヤントー沼 Ho 測線の現地形ならびに現汀線からの距離とイベント堆積物の層厚との対応 ( 上 ), および堆積柱状対比図 ( 下 ). Fig.. Sedimentary columns and stratigraphic correlation of Line Ho in Lake Horokayanto-numa. Correlation of thickness of event deposits with topographic profile (above) and distance from present shoreline along the survey line (below). 313

七山太重野聖之添田雄二古川竜太岡橋久世斎藤健一横山芳春佐竹健治中川充 Ah-1 Ah- Ah-3 Ah- cm Ah-1 Magnetic susceptibility (x -5 SI) 5 5 75 Dry weight (g) 5 15 Sand content (g) 5 15 5 15 5 3 35 5 5 第 9 図.

18 七山太重野聖之添田雄二古川竜太岡橋久世斎藤健一横山芳春佐竹健治中川充 Ah-1 Ah- Ah-3 Ah- cm Ah-1 Magnetic susceptibility (x -5 SI) Dry weight (g) 5 15 Sand content (g) 第 9 図.Ah 測線の軟 X 線写真 ( 上 ) ならびに Ah-1 試料の堆積柱状図と堆積物性値測定結果の対比 ( 下 ). Fig. 9. Radiographs of four samples of line Ah (above) and correlation between the sedimentary column of Ah-1 and three physical properties: magnetic susceptibility, dry weight and sand content (below). Arrows show inverse grading. 31

Tsunam is sand layers w ithin peatatthe historic place ofk okutaijitem ple around A kkeshitow n,eastern H okkaido,japan YujiSoeda 1,FutoshiNanayama 2,

Tsunam is sand layers w ithin peatatthe historic place ofk okutaijitem ple around A kkeshitow n,eastern H okkaido,japan YujiSoeda 1,FutoshiNanayama 2,Nobuhiro Kumasaki 3,Yasuo Tsutsum i 3,HiroshiKurum