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 azuka 3, Minoru Katsuragaw a 3,Goro Yamada 1 and Morio Akamatsu 1 1 (HistoricalMuseum ofhokkaido,soeda@ jg8.so-net.ne.jp) 2 (Institute of Marine Resources and Environm entgsj/aist,nanayam a-f@ aist.go.jp ) 3 Marine Museum ofakkeshi Abstract: Many earthquakes and tsunamis occur along the Pacific coast of eastern Hokkaido. Akkeshi Town area is situated between Kushiro City and Nemuro City and presence of old Kokutaiji Temple which was built in 1804 is known. In the Nikkanki and timber remnants which derived from this temple, descriptions of the 1843 Tokachi earthquake and tsunami are reported. In this study we investigated the lowland of ca. 2.1 m above sea-level that is distributed at the places in front of the previous Kokutaiji Temple and present Kokutaiji Temple. Comparing to Holocene volcanic ashes that are previously reported from eastern Hokkaido, we can suggest that three ash layers just below the surface may be Ta-a (1739), Ko-c2 (1694) and Ta-b (1667). And ash layer of 27 cm below this layer may be correlated to B-Tm (ca. 1,000 yrs BP) and ash layer below 58 cm from this layer may be correlated to Ta-c2 (ca. 2,500 yrs BP). Consequently, we can estimate that the peat was accumulated during past 3,500 years. From the present diatom analysis the following estimation can be pointed out. (1) Fresh water species such as Pinnularia viridis, Navicula elginesis and terrestrial species such as Hanztschia amphioxys, Pinnularia borealis were predominating in almost all peat samples, and from sand layers marine species such as Palaria sulcata, Cocconeis scutellum, Nitzschia granulata are obtained. (2) The individuals from the sand layers were extremely fewer than peat. From this fact we can conclude that the sand layers are marine event sediments which are derived from the ocean. If it compares with stratigraphy of the tsunami events from Kiritappu Marsh and Harutori Lake, tsunami events of Ts2 to Ts10 are clearly included in our samples. Thus, there were nine times of giant tsunamis during past 3,500 years at Akkeshi area as same as other Pacific coast areas of eastern Hokkaido. K eyw ords: A kkeshitow n,k okutaiji,tsunam ideposit,paleoseism ology,k urilsubduction zone,eastern Hokkaido,Pacific O cean
1 1998 1999 2000a,b 2001a,b,c 2002a. b 2000 2000a, b 2001 Saw ai, 2002 3,000 10 9,000 20 2000a 2001a 1 2 1804 1968 48 58 9 60 3 1843 Mt8.2 450m 2 1952 3m 1954 2 15 5 2 2 1 1843 2 8.8 cm 17.8 cm 4.5 cm 3 4 EPM A
5 5 m m 1000 350 1990 1987 1989 Patrick and R eimer, 1966 1975 3.1 A-1 3 3 70 m 1996 2 A-1 75 m A-2 85 m A-3 115 m 5 8m 2 m 2 m 2 A-3 N2/0 7.5Y R3/1 2 cm cm 10cm A-3 9 As1 9 A-3 3.2 A-3 A-3 GL cm 4 5 A-3 2.1m 61 cm 1cm GL 62 cm As1 1 1.2 cm 10Y R3/1 As1 2.8cm GL 66 cm 1 2.5cm 3 cm GL70 cm 2 7.5Y R4/2 Opx-Cpx Opx-Cpx 1997 Ta-a 1739 Ko-c2 1694 Ta-b 1667 Ta-b 2 cm GL 76 cm 5Y 3/1 As2 1.5 3.4 cm As2 2.5cm GL 81.5 cm 5Y R4/1 10Y R4/1 As3 18 26 cm A-3 2
1.5 cm 4 b As3 4 cm GL 101 cm 0.8 cm Y Hb Opx Cpx B-Tm 10 B-Tm 3cm GL 105 cm 10Y R4/1 As4 2 cm As4 4.5cm GL 111 cm 10Y R4/1 As5 1.3 2.2 cm As5 3cm GL 116 cm 10Y R4/1 As6 2 2.6 cm As6 9.5cm GL 127 cm 1.5cm As6 33cm GL 151cm 10Y R4/1 As7 1.5 2.cm As7 5cm GL158cm 1.5cm Ta-c2 2500 Ta-c2 2cm GL162cm 10Y R4/1 As8 8.5 10.3cm A-3 2 As8 5.5cm GL176cm 10Y R4/1 As9 5.5 8 cm 3 As9 10.5cm A-3 GL192cm 10Y 4/1 2 5 1700 m A-4 1730 m A-5 975 m A-4 945 m A-5 A-4 A-5 50cm 10cm 2 Ta-a Ko-c2 A-4 10 cm 15cm
A-5 8cm 10cm 1 2cm A-3 A-4 2 As2 As3 A-5 As2 5 A-3 Ta-b 45 cm Ko-c2 Ta-b H anztschia am phioxys Pinnularia borealis Orthoseira roesana 90 100 10 As2 Palaria sulcata Cocconeis scutellum, Diploneis sm ithii, Actinoptychus senarius, Coscinodiscus sp. 60 As3 Palaria sulcata Cocconeis scutellum Diploneis sm ithii Nitzschia granulata Actinoptychus senarius Navicula m arina Coscinodiscus sp. 95 As2 As3 1 B-Tm Hanztschia am phioxys Pinnularia borealis Orthoseira roesana Pinnularia Navicula Cyclotella striata Coscinodiscus sp. Palaria sulcata 3 B-Tm As6 Hanztschia am phioxys, Pinnularia borealis, Orthoseira roesana Pinnularia viridis P. acrosphaeria P. nodosa Navicula elginensis As4 As5 As6 Pinnularia Navicula Palaria sulcata Cocconeis scutellum Coscinodiscus sp 8 30 5 A-3 As1 As7 9 A-4 As2 As3 A-5 As2 3500 9 1 Pinnularia viridis Navicula elginensis Hanztschia am phioxys Pinnularia borealis Palaria sulcata Cocconeis scutellum Nitzschia granulata 2
As2 As3 10 17 1700m 950m 1952 1843 As1 Ta-a 1739 1843 2 A-3 1843 As1 5 2000a 2001a A-3 As1 As9 Ts2 Ts10 400 500 1 3500 9 2 Ts2 Ts10 3 10 17 As2 As3 1000 m 1952 1843 1996.,23p. 1990 42 73-88 1997 1694 17 18 42 269-279 2001 no.20 2, i-ii 2000a no.31,92-98 2000b no.28,154-161 1987 Diatom 6 23-44 1989 27 1-20 2002a
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