THE PROBLEM OF AGE DETERMINATION ON THE OCCURRENCE TIME OF HUGE TSUNAMI BY CORAL BOULDERS Kunio OMOTO Nihon University, Tokyo JAPAN omoto@chs.nihon-u.ac.jp France 1
Index map of surveyed Miyako Island, SW Japan. mark indicates epicenter of the 1771 Meiwa earthquake. France 2
The 1771 Meiwa tsunami France 3
One of the tsunami boulders lay beached on 10m high marine terrace, southeast of Ishigaki Island. France 4
One of the tsunami boulders lay beached on 20m high marine terrace, southeast of Miyako Island. France 5
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
Air photo of Higashihenna promontory and Maibahbama, SE of Miyako Island France 7
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
Air view of tsunami boulders beached on the west of Maibahbama,SE E of Miyako Island. Red fringed boulders indicate Genus Porites sp. 9
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-1985-1.817 169 57 550 0 1,879 1,712 1,808 0 1,771 ±60 0 NUTA2-15498 3.200 92 24 558 8 1,842 1,711 1,793 15 1,771 ±60 0 NU-2105-0.694 227 54 627 69 1,810 1,661 1,731 62 1,771 ±60 0 NU-2110-1.228 266 55 657 30 1,772 1,624 1,687 44 1,771 ±60 0 NU-2116 0.631 261 55 684 27 1,704 1,560 1,652 (119) 1,633 ±17 138 NU-2109 0.547 281 55 702 18 1,687 1,557 1,630 22 1,633 ±17 NU-2115 0.798 288 55 714 12 1,677 1,552 1,618 12 1,633 ±17 NU-2106-0.343 370 55 776 62 1,635 1,512 1,570 (63) 1,557 ±14 76 NU-2132-1.464 421 46 808 32 1,592 1,479 1,543 27 1,557 ±14 NU-2103-1.195 479 56 871 63 1,534 1,433 1,488 (69) 1,488 69 NU-1991-1.163 592 57 984 113 1,446 1,347 1,399 (89 ) 1,399 89 NU-1983 0.397 647 49 1,066 82 1,395 1,304 1,348 (51) 1,325 ±28 74 NU-2111 0.868 661 57 1,088 22 1,391 1,287 1,331 17 1,325 ±28 NU-1992-0.906 697 47 1,094 6 1,360 1,284 1,326 5 1,325 ±28 NU-2117 0.617 710 57 1,132 38 1,342 1,230 1,293 33 1,325 ±28 NU-1969-1.290 815 60 1,205 73 1,294 1,175 1,229 (96) 1,229 96 France 10
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
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
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-1985 1,808 0 1,771 50 NUTA2-15498 1,793 15 1,771 ±60 25 NU-2105 1,731 62 1,771 29 NU-2110 1,687 44 1,771 34 NU-2116 1,652 (119) 1,633 138 28 NU-2109 1,630 22 1,633 ±17 33 NU-2115 1,618 12 1,633 26 NU-2106 1,570 (63) 1,557 76 41 NU-2132 1,543 27 1,557 ±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
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
Calibrated ages(ad or BC) ) of coral boulders AD or BC 15
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
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
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
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
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
Relationship between distribution of hypocenters and four plates (Prim. Min. Jap. Gov., 1997) France 21
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
Direction of the 1771 Meiwa tsunami France 23
Schematic model showing transport process of tsunami boulders France 24
Schematic model showing typhoon attack and coral colonies France 25
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-1985 1,808 0 1,771 ±60 0 9 NU-1984 1,165 64 1,141 ±24 88 50 NUTA2-15498 1,793 15 1,771 ±60 0 7 NU-1982 1,117 48 1,141 ±24 25 NU-2105 1,731 62 1,771 ±60 0 12 NU-1987 974 (167) 920 ±50 221 29 NU-2110 1,687 44 1,771 ±60 0 18 NU-1993 932 42 920 ±50 34 NU-2116 1,652 (119) 1,633 ±17 138 6 NU-1981 899 33 920 ±50 28 NU-2109 1,630 22 1,633 ±17 11 NU-1986 874 25 920 ±50 33 NU-2115 1,618 12 1,633 ±17 36 NU-2118 723 (197) 728 ±5 26 NU-2106 1,570 (63) 1,557 ±14 76 19 NU-1999 733 10 728 ±5 192 41 NU-2132 1,543 27 1,557 ±14 22 NU-2102 596 (132) 596 132 23 NU-2103 1,488 (69) 1,488 69 5 NU-1980 395 201 395 201 16 NU-1991 1,399 89 1,399 89 42 NU-1989 217 178 204 ±13 191 8 NU-1983 1,348 51 1,325 ±28 74 20 NU-2100 191 26 204 ±13 30 NU-2111 1,331 17 1,325 ±28 21 NU-2101 118 73 118 86 17 NU-1992 1,326 5 1,325 ±28 41 NU-2136-252 370-252 370 35 NU-2117 1,293 33 1,325 ±28 Aver 39 118 1 NU-1969 1,229 (96) 1,229 96 2 6