141°0'0"E

141°0'0"E

38°0'0"N

38°0'0"N

Effect of the 9.0M Ea rthqua ke a nd Tsuna mi on the popula tionof S enda i, J a pa n

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Tectonic Situation

9.0 ML Earthquake

155°E

155°E

150°E

150°E

145°E

145°E

140°E

140°E

135°E

135°E

130°E

130°E

45°N

45°N

40°N

40°N

35°N

35°N

30°N

30°N

Magnitude6 - 6.56.51 - 77.1 - 7.57.51 - 88.1 - 9

Depth Km0 - 2425 - 4950 - 149150 - 588Tectonic pla te bounda ries

Q

143°E

143°E

142°E

142°E

141°E

141°E

140°E

140°E

139°E

139°E

138°E

138°E

40°N

39°N

38°N

37°N

Magnitude6 - 6.56.51 - 77.1 - 7.57.51 - 8

8.1 - 9

Depth0 - 2425 - 2930 - 3940 - 166

Peak Ground AccelerationValue

High

Low

Q9.0M Ea rthqua ke

Tsunami Flood ZoneWater Depth (m)

1 - 34 - 56 - 8

The Tsunami

0 100 200 300 40050Miles

0 6 12 18 243 Miles

0 25 50 75 10012.5Miles

0 6 12 18 243Miles

8m Tsunami Population Affected

0 - 10001001 - 1000010001 - 2500025001 - 5000050001 - 100000

Prefecture % Land area affected Population of prefecture Tsunami affected populationS enda i-shi, T a iha ku-ku 99.06 224,558 222,439R ifu-cho 98.56 36,029 35,512Ona ga wa -cho 90.56 7,512 6,802S oma -shi 86.70 36,195 31,381Ishinoma ki-shi 86.36 150,966 130,370Ma tsushima -ma chi 84.74 15,062 12,765S hinchi-ma chi 82.87 7,957 6,594Na tori-shi 75.05 74,740 56,089Y a ma moto-cho 69.49 13,234 9,195S enda i-shi, Miya gino-ku 64.14 187,306 120,136S hichiga ha ma -ma chi 60.61 19,728 11,963Wa ta ri-cho 60.46 33,942 20,524T a ga jo-shi 54.82 62,203 34,108S enda i-shi, Wa ka ba ya shi-ku 54.12 130,107 70,406Iwa numa -shi 53.63 43,788 23,485Higa shima tsushima -shi 53.11 40,221 21,359S hioga ma -shi 52.95 56,256 29,785S hioga ma -shi 47.05 56,256 26,471Higa shima tsushima -shi 46.90 40,221 18,862Iwa numa -shi 46.37 43,788 20,303S enda i-shi, Wa ka ba ya shi-ku 45.88 130,107 59,701T a ga jo-shi 45.18 62,203 28,095Wa ta ri-cho 39.54 33,942 13,418S hichiga ha ma -ma chi 39.39 19,728 7,765S enda i-shi, Miya gino-ku 35.86 187,306 67,170Y a ma moto-cho 30.52 13,234 4,039Na tori-shi 24.95 74,740 18,651S hinchi-ma chi 17.13 7,957 1,363Ma tsushima -ma chi 15.24 15,062 2,297Ishinoma ki-shi 13.64 150,966 20,596S oma -shi 13.30 36,195 4,814Ona ga wa -cho 9.45 7,512 710R ifu-cho 1.44 36,029 517S enda i-shi, T a iha ku-ku 0.94 224,558 2,119Total 2,279,608 1,139,804

Methodology

Aim

Results and Discussion

T his poster collects a nd presents va rious sources of da ta a va ila ble to estima te numbers of those directly a ffected by the 9.0M tsuna mi, a s well a s provide some historica l context for the event which occurred a t 14:46:18 J S T on 11th of Ma rch, 2011. By combining sepa ra tely a va ila ble sources of da ta to produce new a dditiona l da ta sets, with scope to estima te the number of the popula tion directly a ffected by the tsuna mi flood wa ters. T his will be a chieved by modelling a n 8 m tsuna mi inunda tion on the S enda i coa sta l region a nd combining this with census da ta by prefecture.

J a pa n la ys on the western edge of the pla te bounda ry between the Pa cific a nd North America n pla tes. At this a ctive pla te ma rgin, the Pa cific pla te is being subducted a t a ra te of a pproxima tely 83mm/yr (S eno et a l., 1996), forming a deep region benea th the sea known a s the J a pa n Trench. Over the pa st 100 yea rs, the inter-pla te bounda ry to the north-ea st of J a pa n ha s hosted ma ny sma ller ea rthqua kes up 7.8M, with the region ha ving hosted 9 events grea ter tha n 7 in ma gnitude since 1973 (Ha shimoto et a l., 2009). T he la st time a n ea rthqua ke with compa ra ble ma gnitude a nd loca tion occurred wa s the J oga n Ea rthqua ke, 13th J uly, 869. T his tsuna mi left sediment deposits kilometres in sca le on the S enda i pla in (Minoura et a l., 2001) with a n estima ted ma gnitude of 8.2 (Fujii et a l., 2011) which ca used a round 1000 dea ths a ccording to historica l documents. T he 2011 Ea rthqua ke, is a rela tively ra re disa ster which occurred in a n a ctive pla te bounda ry, fa r surpa ssing other ea rthqua kes from the J a pa n Trench.

In a tota l of 44 prefectures with a tota l popula tion of 1,778,052, 628,890 (35.4 %) were directly a ffected by the tsuna mi.T he prefectures most a ffected by the inunda tion were S enda i T a iha ku-ku, Ishinoma ki-shi, S enda i Miya gino-ku a nd S enda i Wa ka ba ya shi-ku. With Popula tions a ll over 130,000 a nd over 54 % tsuna mi a ffected la nd. Collectively, S enda i a nd its districts (ku) ha s a popula tion of 317,413, with a tota l 137,576 directly a ffected, a pproxima tely 43.3 % (Miya gino - 35.9 %, Wa ka ba ya shi - 54.1 %). T hese prefectures ha ve a high popula tion density, which despite only a round 40 % of the la nd wa s a ffected, tens of thousa nds of people were displa ced a s a result. In contra st Ona ga wa , which despite ha ving 90.8 % of the la nd covered by the tsuna mi, 710 people were a ffected due to the low popula tion of people in this rura l region. Other significa nt prefectures impa cted a re a s follows with most %Popula tion a ffected first: S oma - 36,195 (87 %), Wa ta ri - 33,942 (60.4 %), Iwa numa - 43,788 (53.6 %), S hioga ma - 56,256, (52.9 %), Na tori - 18,051 (24.2 %), Ishinoma ki - 20,596 (13.6 %) a nd Ona gowa - 710 (9.5 %). Other prefectures ca n be referenced from the ta ble.When compa red to results produced by Center for S a tellite Ba sed Crisis Informa tion (DL R ), T he results a re compa ra ble. DL R 's study concluded 12% of the the 1,000,200 were a ffected, where a s my results conclude 35.4% of 1,778,052 were rea ched by flood wa ters. DL R published their results on the 18th of ma rch, 2011, using la ndsa t da ta a cquired from the 12th of ma rch. T his difference in a pproa ch could a ccount for the differing results. For exa mple, ma nma de structures not seen in the DEM ha ve a n effect, which ma y sheltered some a rea s of S enda i from inunda tion, thus lessening the numbers of those a ffected. Da ta relea sed by T he Na tiona l Police Agency sta te, there were 15,840 dea ths, with 3,607 missing. 92.5% of these dea ths a re a ttributed to the tsuna mi flood wa ters (http://www.npa .go.jp/a rchive/keibi/biki/higa ijokyo_ e.pdf) a fa ta lity ra te of 1.09% for the a ffected popula tion of 1,778,052.T he limita tions for the method used in this study a re a s a result of the a ssumptions ma de. As the da ta freely a va ila ble wa s popula tion per prefecture, this mea nt a ssumptions ha d to be ma de tha t the popula tion of ea ch prefecture wa s evenly distributed over the la nd. In rea lity popula tions a re not evenly distributed a nd a re focused on cities, towns a nd villa ges, which wa s not a ble to be included in this study. T he method could be improved if popula tion density da ta wa s loca ted.An a dditiona l limit of this method is the 8 m tsuna mi flood model. T his va lue wa s chosen a s the a vera ge from (Tsuji et a l., 2010) pa per. Of course in rea lity the wa ve height a t the coa st will va ry depending on conditions such a s shore depth a nd slope a ngle.Using the results of this study it ma y be possible to fla g popula tions for coa sta l defence development, pa rticula rly those of the S enda i districts which were ba dly da ma ged. S cope for future study would include, cost per unit coa sta l defence wa ll, or possible sea bed exca va tion to reduce slope a ngle.

±

Abe T, Goto K, S uga wa ra D (2012) R ela tionship between the ma ximum extent of tsuna mi sa nd a nd the inunda tion limit of the 2011 Tohoku-oki tsuna mi on the S enda i Pla in, J a pa n. S ediment

Geol 282:142–150Fujii, Y., K. S a ta ke, S . S a ka i, M. S hinoha ra , a nd T. Ka na za wa (2011), T suna mi source of the 2011 off the Pa cific coa st of

Tohoku, J a pa n ea rthqua ke, Ea rth Pla nets S pa ce, 63(7), 815–820, doi:10.5047/eps.2011.06.010.

Minoura , K., F. Ima mura , D. S uga wa ra , Y. Kono, a nd T. Iwa shita (2001), T he 869 J oga n tsuna mi deposit a nd recurrence interva l of la rge-sca le tsuna mi on the Pa cific coa st of northea st J a pa n, J. Na t.

Disa ster S ci., 23(2), 83–88.Ha shimoto, C., A. Noda , T. S a giya , a nd M. Ma tsu’ura (2009),

Interpla te seismogenic zones a long the Kuril‐ J a pa n trench inferred from GPS da ta inversion, Na t. Geosci., 2, 141–144.

S eno, T., T. S a kura i, a nd S . S tein (1996), Ca n the Okhotst pla te bediscrimina ted from the North America n pla te?, J. Geophys. R es.,

101, 11,305–11,315.Tsuji, Y ., T. T a ka ha shi, a nd K. Ima i (2010), Compa rison of tsuna mi height distributions of the 1960 a nd the 2010 Chilea n ea rthqua kes on the coa sts of the J a pa nese Isla nds, Abstra ct G36A-0832

presented a t 2010 Fa ll Meeting, AGU, S a n Fra ncisco, Ca lif., 13–17 Dec.

References