This document analyzes the population affected by the 2011 9.0 magnitude earthquake and tsunami in Japan. It estimates that over 1.1 million people in 44 prefectures were directly impacted by the tsunami flooding. The prefectures of Sendai Taihaku-ku, Ishinomaki-shi, Sendai Miyagino-ku, and Sendai Wakabayashi-ku had the highest numbers affected, with populations over 130,000 and over 54% of land area inundated. While limitations exist in the methodology, this analysis provides estimates of populations affected that can help inform future coastal defense planning.

1. 141°0'0"E
141°0'0"E
38°0'0"N
38°0'0"N
Effectofthe 9.0MEa rthqua ke a nd T suna mionthe popula tion
ofS 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
Magnitude
6-6.5
6.51-7
7.1-7.5
7.51-8
8.1-9
Depth Km
0-24
25-49
50-149
150-588
T ectonic 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°N39°N38°N37°N
Magnitude
6-6.5
6.51-7
7.1-7.5
7.51-8
8.1-9
Depth
0-24
25-29
30-39
40-166
Peak Ground Acceleration
Value
High
L ow
Q9.0MEa rthqua ke
Tsunami Flood Zone
Water Depth (m)
1 - 3
4 - 5
6 - 8
The Tsunami
0 100 200 300 40050
Miles
0 6 12 18 243
Miles
0 25 50 75 10012.5
Miles
0 6 12 18 243
Miles
8m Tsunami
Population Affected
0 - 1000
1001 - 10000
10001 - 25000
25001 - 50000
50001 - 100000
Prefecture % Land area affected Population of prefecture Tsunami affected population
S enda i-shi,T a iha ku-ku 99.06 224,558 222,439
R ifu-cho 98.56 36,029 35,512
Ona ga wa -cho 90.56 7,512 6,802
S oma -shi 86.70 36,195 31,381
Ishinoma ki-shi 86.36 150,966 130,370
Ma tsushima -ma chi 84.74 15,062 12,765
S hinchi-ma chi 82.87 7,957 6,594
Na tori-shi 75.05 74,740 56,089
Y a ma moto-cho 69.49 13,234 9,195
S enda i-shi,Miya gino-ku 64.14 187,306 120,136
S hichiga ha ma -ma chi 60.61 19,728 11,963
Wa ta ri-cho 60.46 33,942 20,524
T a ga jo-shi 54.82 62,203 34,108
S enda i-shi,Wa ka ba ya shi-ku 54.12 130,107 70,406
Iwa numa -shi 53.63 43,788 23,485
Higa shima tsushima -shi 53.11 40,221 21,359
S hioga ma -shi 52.95 56,256 29,785
S hioga ma -shi 47.05 56,256 26,471
Higa shima tsushima -shi 46.90 40,221 18,862
Iwa numa -shi 46.37 43,788 20,303
S enda i-shi,Wa ka ba ya shi-ku 45.88 130,107 59,701
T a ga jo-shi 45.18 62,203 28,095
Wa ta ri-cho 39.54 33,942 13,418
S hichiga ha ma -ma chi 39.39 19,728 7,765
S enda i-shi,Miya gino-ku 35.86 187,306 67,170
Y a ma moto-cho 30.52 13,234 4,039
Na tori-shi 24.95 74,740 18,651
S hinchi-ma chi 17.13 7,957 1,363
Ma tsushima -ma chi 15.24 15,062 2,297
Ishinoma ki-shi 13.64 150,966 20,596
S oma -shi 13.30 36,195 4,814
Ona ga wa -cho 9.45 7,512 710
R ifu-cho 1.44 36,029 517
S enda i-shi,T a iha ku-ku 0.94 224,558 2,119
Total 2,279,608 1,139,804
Methodology
Aim
Results and Discussion
T hispostercollectsa nd presentsva rioussourcesofda ta a va ila ble toestima te numbersofthose directlya ffected bythe 9.0Mtsuna mi,a swell a s
provide some historica l contextforthe eventwhich occurred a t14:46:18J S T on11th ofMa rch,2011.Bycombining sepa ra telya va ila ble sources
ofda ta toproduce new a dditiona l da ta sets,with scope toestima te the numberofthe popula tiondirectlya ffected bythe tsuna miflood wa ters.T his
will be a chieved bymodelling a n8mtsuna miinunda tiononthe S enda icoa sta l regiona nd combining thiswith censusda ta byprefecture.
J a pa nla ysonthe westernedge ofthe pla te bounda rybetweenthe
Pa cific a nd North America npla tes.Atthisa ctive pla te ma rgin,the
Pa cific pla te isbeing subducted a ta ra te ofa pproxima tely83mm/yr
(S enoeta l.,1996),forming a deepregionbenea th the sea knowna s
the J a pa nT rench.Overthe pa st100yea rs,the inter-pla te bounda ry
tothe north-ea stofJ a pa nha shosted ma nysma llerea rthqua kesup
7.8M,with the regionha ving hosted 9eventsgrea tertha n7in
ma gnitude since 1973(Ha shimotoeta l.,2009).
T he la sttime a nea rthqua ke with compa ra ble ma gnitude a nd loca tion
occurred wa sthe J oga nEa rthqua ke,13th J uly,869.T histsuna mi
leftsedimentdepositskilometresinsca le onthe S enda ipla in
(Minoura eta l.,2001)with a nestima ted ma gnitude of8.2
(Fujiieta l.,2011)which ca used a round 1000dea thsa ccording to
historica l documents.T he 2011Ea rthqua ke,isa rela tivelyra re
disa sterwhich occurred ina na ctive pla te bounda ry,fa rsurpa ssing
otherea rthqua kesfromthe J a pa nT rench.
Ina tota l of44prefectureswith a tota l popula tionof1,778,052,
628,890(35.4%)were directlya ffected bythe tsuna mi.T he
prefecturesmosta ffected bythe inunda tionwere S enda iTa iha ku-
ku,Ishinoma ki-shi,S enda iMiya gino-kua nd S enda iWa ka ba ya shi-
ku.With Popula tionsa ll over130,000a nd over54%tsuna mi
a ffected la nd.Collectively,S enda ia nd itsdistricts(ku)ha sa
popula tionof317,413,with a tota l 137,576directlya ffected,
a pproxima tely43.3% (Miya gino-35.9%,Wa ka ba ya shi-54.1%).
T hese prefecturesha ve a high popula tiondensity,which despite
onlya round 40%ofthe la nd wa sa ffected,tensofthousa ndsof
people were displa ced a sa result.Incontra stOna ga wa ,which
despite ha ving 90.8% ofthe la nd covered bythe tsuna mi,710
people were a ffected due tothe low popula tionofpeople inthis
rura l region.Othersignifica ntprefecturesimpa cted a re a sfollows
with most%Popula tiona 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%).Otherprefecturesca nbe referenced from
the ta ble.
Whencompa red toresultsproduced byCenterforS a tellite Ba sed
CrisisInforma tion(DL R ),T he resultsa re compa ra ble.DL R 'sstudy
concluded 12% ofthe the 1,000,200were a ffected,where a smy
resultsconclude 35.4% of1,778,052were rea ched byflood wa ters.
DL R published theirresultsonthe 18th ofma rch,2011,using
la ndsa tda ta a cquired fromthe 12th ofma rch.T hisdifference in
a pproa ch could a ccountforthe differing results.Forexa mple,
ma nma de structuresnotseeninthe DEMha ve a neffect,which
ma ysheltered some a rea sofS enda ifrominunda tion,thuslessening
the numbersofthose a ffected.Da ta relea sed byT he Na tiona l
Police Agencysta te,there were 15,840dea ths,with 3,607missing.
92.5% ofthese dea thsa re a ttributed tothe tsuna miflood wa ters
(http://www.npa .go.jp/a rchive/keibi/biki/higa ijokyo_ e.pdf)a
fa ta lityra te of1.09%forthe a ffected popula tionof1,778,052.
T he limita tionsforthe method used inthisstudya re a sa resultof
the a ssumptionsma de.Asthe da ta freelya va ila ble wa spopula tion
perprefecture,thismea nta ssumptionsha d tobe ma de tha tthe
popula tionofea ch prefecture wa sevenlydistributed overthe la nd.
Inrea litypopula tionsa re notevenlydistributed a nd a re focused on
cities,townsa nd villa ges,which wa snota ble tobe included inthis
study.T he method could be improved ifpopula tiondensityda ta
wa sloca ted.
Ana dditiona l limitofthismethod isthe 8mtsuna miflood model.
T hisva lue wa schosena sthe a vera ge from(T sujieta l.,2010)
pa per.Ofcourse inrea litythe wa ve heighta tthe coa stwill va ry
depending onconditionssuch a sshore depth a nd slope a ngle.
Using the resultsofthisstudyitma ybe possible tofla g popula tions
forcoa sta l defence development,pa rticula rlythose ofthe S enda i
districtswhich were ba dlyda ma ged.S cope forfuture studywould
include,costperunitcoa sta l defence wa ll,orpossible sea bed
exca va tiontoreduce slope a ngle.
±
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ma ximum extentoftsuna misa nd a nd the inunda tionlimitofthe
2011T ohoku-okitsuna mionthe S enda iPla in,J a pa n.S ediment
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References