THE PROBLEM OF AGE DETERMINATION ON THE OCCURRENCE TIME OF HUGE TSUNAMI BY CORAL BOULDERS. Kunio OMOTO Nihon University, Tokyo JAPAN

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1 THE PROBLEM OF AGE DETERMINATION ON THE OCCURRENCE TIME OF HUGE TSUNAMI BY CORAL BOULDERS Kunio OMOTO Nihon University, Tokyo JAPAN France 1

2 Index map of surveyed Miyako Island, SW Japan. mark indicates epicenter of the 1771 Meiwa earthquake. France 2

3 The 1771 Meiwa tsunami France 3

4 One of the tsunami boulders lay beached on 10m high marine terrace, southeast of Ishigaki Island. France 4

5 One of the tsunami boulders lay beached on 20m high marine terrace, southeast of Miyako Island. France 5

6 Objectives: 1. Elucidate discordance between 14 C ages of coral boulders and the 1771 Meiwa tsunami. 2. Determine timings of the past huge tsunamis by calibrated ages of coral boulders. 3. Compare 14 C ages of Miyako Island with 14 C ages of other Sakishima Islands. 4. Calculate periodicity and/or recurrent intervals in order to predict next huge earthquake and tsunami. France 6

7 Air photo of Higashihenna promontory and Maibahbama, SE of Miyako Island France 7

8 Coastal view of Maibahbama. Flat topped surface indicates 20m high marine terrace of Higashihenna promontory. Beach rocks indicated1,200-1,340 cal BP (Omoto 2010). France 8

9 Air view of tsunami boulders beached on the west of Maibahbama,SE E of Miyako Island. Red fringed boulders indicate Genus Porites sp. 9

10 2010/8/1 Calibrated Ages of Tsunami Boulders collected from Miyako Island Code No. δ 13 C Raw ± Conv. D-1 Cal(Up) Cal(Low) Cal (M) D-2 Aver Range D-3 NU ,879 1,712 1, ,771 ±60 0 NUTA ,842 1,711 1, ,771 ±60 0 NU ,810 1,661 1, ,771 ±60 0 NU ,772 1,624 1, ,771 ±60 0 NU ,704 1,560 1,652 (119) 1,633 ± NU ,687 1,557 1, ,633 ±17 NU ,677 1,552 1, ,633 ±17 NU ,635 1,512 1,570 (63) 1,557 ±14 76 NU ,592 1,479 1, ,557 ±14 NU ,534 1,433 1,488 (69) 1, NU ,446 1,347 1,399 (89 ) 1, NU , ,395 1,304 1,348 (51) 1,325 ±28 74 NU , ,391 1,287 1, ,325 ±28 NU , ,360 1,284 1, ,325 ±28 NU , ,342 1,230 1, ,325 ±28 NU , ,294 1,175 1,229 (96) 1, France 10

11 Discussions: 1. Causes of discordance between 14 C ages and the 1771 Meiwa tsunami. 2. Timings of the past huge tsunamis referring to the previous reports. 3. Periodicity and/or recurrent intervals of the past huge tsunamis. France 11

12 Discussion-1: 1. Causes of discordance (1) Radiocarbon ages used in previous studies were raw 14 C ages without isotope analysis. (2) Coral samples provided for 14 C datings have already lost their surface layers during transportation. (3) Some coral boulders might have been transported by high waves of typhoons. (4) Some coral boulders might have been transported by the past multiple tsunamis. France 12

13 Table 2 An example of calculation of the timings and recurrent intervals of the past huge tsunamis. Sp. Nr. Code No. Cal (M) D-2 AVR Range RI 10 NU , , NUTA , ,771 ±60 25 NU , , NU , , NU ,652 (119) 1, NU , ,633 ±17 33 NU , , NU ,570 (63) 1, NU , ,557 ±14 Figure of AVR indicates averaged timing of the past huge tsunamis. Figure of RI indicates recurrent interval (difference from former AVR) of the past huge tsunami. 13

14 Discussion-2: 2. Timings of the past huge tsunamis prior to the Meiwa tsunami were calculated by average values of adjacent calibrated ages. Huge tsunamis have generated 14 times between AD 1633 and BC 252. AD 1633±17, 17, 1576±6, 6, 1488, 1399, 1325±28, 28, 1229, 1141±24, 920±50, 728±5, 596, 395, 204±13, 118 and BC 252. The AD 1633 tsunami coincided with historical record of AD 1667 tsunami within a margin of error. France 14

15 Calibrated ages(ad or BC) ) of coral boulders AD or BC 15

16 3. Correlation of timings of the past huge tsunamis with other Sakishima Islands. Ages are expressed with raw 14 C ages. Upper timings were compiled by Kawana and Nakata (1994). Lower ages indicate averaged raw 14 C ages of Miyako Island (this study). France 16

17 Discussion-4: 4. Periodicity and/or recurrent intervals of tsunamis. The rounded average recurrent intervals were 80±20, 140±10, 10, 200±20 and 370y respectively. France 17

18 Conclusions 1. Four of 36 samples coincided with the 1771 Meiwa tsunami within a margin of error. Other samples indicated far older ages. The causes of discordance were erroneous use of 14 C age, under estimation of lost layers of coral samples, and due to past multiple huge tsunamis. 2. Timings of huge tsunamis prior to the 1771 Meiwa tsunami generated 14 times between AD 1633 and BC 252y. 3. Rounded periodicity and/or recurrent intervals of tsunamis were 80±20, 140±10, 10, 200±20 and 370y respectively. France 18

19 Acknowledgements I express my gratitude to Prof. Toshio Nakamura,, AMS facility of Nagoya University who kindly determined the age of fossil shell collected ed from one of the tsunami boulders and to Professor William D. Patterson, Department of English, College of Humanities and Sciences, Nihon University who kindly corrected my English. I also wish to thank Mr. Akira Adaniya,, Chief of the Committee Members of the Miyakojima City Museum who suggested studying coral boulders of Maibahbama. Thanks also go to Mr. Mitsugu Kugai,, Miyako City Museum, who helped with the surveying of the tsunami boulders. The field surveys and 14 C dating were partly supported by the Educational Board of Miyakojima City and by a Scientific Grant in Aid from the College of Humanities and Sciences, Nihon University. France 19

20 Finally We are now able to obtain accurate calibrated ages and correlate them with the historical records of the past huge earthquakes and tsunamis for Sakishima Islands. These results would contribute when we estimate the recurrence time of huge earthquake that may generate in the Ryukyu Trench and Okinawa Trough. We will never forget an old Japanese proverb. Huge disaster shall repeat when we began to forget former event. Thank you very much! France 20

21 Relationship between distribution of hypocenters and four plates (Prim. Min. Jap. Gov., 1997) France 21

22 Discussion Transport process of tsunami boulders (1) Direction of tsunami: SW off of Miyako Island. (2) The run-up up height: ca. 5m at Maibahbama. (3) Tsunami attack: Maibahbama was protected by Myadohzaki promontory. (4) Transport process: Counter clock flows. (5) High wave of typhoons: seldom exceed 3m. France 22

23 Direction of the 1771 Meiwa tsunami France 23

24 Schematic model showing transport process of tsunami boulders France 24

25 Schematic model showing typhoon attack and coral colonies France 25

26 Discussion-2: 2. Calculation of timings of huge tsunamis Nr Code No. Cal D-2 Aver Range D-3 Nr Code No. Cal D-2 Aver Range D-3 10 NU , ,771 ± NU , ,141 ± NUTA , ,771 ± NU , ,141 ±24 25 NU , ,771 ± NU (167) 920 ± NU , ,771 ± NU ±50 34 NU ,652 (119) 1,633 ± NU ±50 28 NU , ,633 ±17 11 NU ±50 33 NU , ,633 ±17 36 NU (197) 728 ±5 26 NU ,570 (63) 1,557 ± NU ± NU , ,557 ±14 22 NU (132) NU ,488 (69) 1, NU NU , , NU ± NU , ,325 ± NU ±13 30 NU , ,325 ±28 21 NU NU , ,325 ±28 41 NU NU , ,325 ±28 Aver NU ,229 (96) 1,

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