Minami-Sanriku town field trip (17 March 2013)
By Anawat Suppasri, Abdul Muhari, Fumihiko Imamura, IRIDeS, Tohoku University
1. Background of tsunamis in Tohoku region
There were three major tsunami events that attacked Tohoku region including
Minama-Sanriku town in the last century. They are 1896 Meiji-Sanriku, 1933 Showa-Sanriku
and 1960 Chile tsunami respectively (Fig. 1 and Table 1). The 1896 event was atsunami-earthquake event, a small shake causing large tsunami. This event was occurred atnight and thus most of residence ignored evacuation. The second event happened 37 years
later in 1933. Though the earthquake occurred at night again but total loss was significantly
reduced owing to the experience from the previous event and smaller tsunami height. At thesame time, there was still some misunderstanding based on the experience from the 1896
event that ‘only’ small shake generates large tsunami that led some people ignored theevacuation in the 1933 event. The third event is the 1960 Chili tsunami. It was generated by
the great earthquake in Chile 1960 propagated across the Pacific Ocean and attacked theTohoku coast in the early morning of the following day. At that time, there was no available
knowledge for the far-field tsunami and their related protection system.
Before the 2011 event, there was a 99 % probability that another M 7.5-8.0 earthquake would
strike off the Miyagi Prefecture within the next 30 years. A series of M7.4-M8.0 earthquakes
have occurred in the Miyagi Sea since 1793, and the average time between them is 37 years.
Many countermeasures have been constructed in preparation for this tsunami, which may
cause damage to the Sanriku coast and the Sendai plain. However, the 2011 tsunami wasgenerated by M9.0 earthquake which caused much more damage than the previousestimation.

41

Latitude4039

2011 Heisei

381960 Chile
1933 Showa
1896 Meiji
1611 Keicho

37
01020
30
40
Maximum tsunami hegiht (m)Fig. 1 Historical tsunamis in the Sanriku area and their maximum tsunami heights
12. Route and schedule
UtatsuShopping village
Shizugawa

Kanyo hotel
Red line: The 2011
tsunamiinundation limit

ToguraFig. 2 Area map of Minami-Sanriku town and field trip route
Table 2 Field trip schedule
TimeArea
9:00 – 9:15
Leave for Utazu
9:15 – 10:00 Utatsu area
10:00 – 10:15 Leave for Shizugawa
10:15 – 11:45 Shizugawa area

11:45 – 12:00
12:00 – 13:30
13:30 – 13:45
13:45 – 14:00
14:00

Leave for shopping village
Shopping village
Leave for Togura
Togura area
Leave for Sendai

Activities
Utatsu Ohashi bridge, temporary houses
and surrounding areas
Tsunami gate, memorial stones, disasterprevention building and JR train station,
Shizugawa Elementary School
Lunch and souvenir
Tsunami mark and damage areas

3. Minami-Sanriku before the 2011 tsunami
Minami-Sanriku is a town with prosperous fisheries and a population of about 18,000. In
Minami-Sanriku, the culture of a silver salmon, scallops, and oysters are prosperous. Becauseof their economic importance, tsunami–induced damage to these aqua-cultural facilities is agrave concern. The 1960 Chilean Tsunami caused great damage to Minami-Sanriku. On theoccasion of the 30th anniversary of the 1960 Chilean Tsunami, a Moai monument wasreceived as a symbol of friendship with Chile, which also had a stricken area. The Moaimonument was installed in Matsubara Park (Fig. 3-left) where inundation signs (Fig. 3-right)
were also installed. Tidal gate was installed near to the park and a private apartment nearby
the park is designated as evacuation shelter (Fig. 4-right). The 1896 Meiji-Sanriku Tsunami
height was 7 m here; 441 people were killed. The 1960 Chilean Tsunami height was 5.5 m. It
washed away or destroyed 965 houses.
2Fig. 3 Moai monument of the 1960 Chile tsunami (27/5/2008) and tsunami inundation markof the Chile tsunami (27/5/2008)

Fig. 4 Automatic tidal gate (27/5/2008) and evacuation building (27/5/2008)
4. Minami-Sanriku after the 2011 tsunami
In Minami-Sanriku, seawalls (+4.6 m) and tidal gates (+10 m) were constructed after the1960 Chile tsunami. The town was fully protected from the tsunami generated in Tokachi Sea
in the east coast of Hokkaido in 1968. However, these were not high enough for the 2011
tsunami which approximately greater than 10 m in every area. About 52% of the town area
was inundated and destroyed 3,301 houses. The total reported death and missing is 695 fromthe approximated population inside inundation area of 14,389 (Total = 17,666). Total numberof evacuee was 9,753 during the peak in 20th March 2011.
Table 1 Summary of major tsunamis in Tohoku region and impact to Minami-Sanriku
EventTime

Mw

Tsunami (m)Meiji

15 Jun 1896
8:10 PM

8.0

12.6

Showa

3 Mar 1933
3:05 AM

8.4

10.5

Chile

24 May 1960
4:30 AM

9.5

5.6Tohoku

11 March 2011
3:20 PM9.0

23.9
3Casualty
Shizugawa = 441
Utatsu = 799Total = 1,240
Shizugawa = 1
Utatsu = 86
Total = 87
Shizugawa = 41
Utatsu = 0
Total = 41

Damaged house
Shizugawa = 267
Utatsu = 306
Total = 573
Shizugawa = 16
Utatsu = 72
Total = 88
Shizugawa = 1,329
Utatsu = 13
Total = 1,342

Total = 695

Total = 3,301

4.1 Utatsu area
Utatsu Ohashi Bridge: VDO taken by survivors shows the moment of tsunami attacking
Utatsu area and the Utatsu Ohashi Bridge (Fig. 5) and tsunami also came from the back side.
The destroyed bridge is a typical example damage type of many bridges found in the 2011
event. Bridges were designed well enough against earthquake force but not for thehydrodynamic force including uplifting force by tsunami.
Mishima Shrine: A shrine called Mishima shrine (Fig. 6–right) that survived the 2011 tsunami
located in a hill slope near to the bridge. There was large number of shrines that survived thetsunami. One of the main reasons is that experiences of historical tsunamis must betransferred as the shrines were built or re-built outside tsunami inundation zone of thehistorical events.

Fig. 5 Utatsu Ohashi Bridge (28/7/2012)

Fig. 6 Tsunami debris (28/7/2012) and Mishima Shrine (28/7/2012)
4.2 Shiuzugawa and Togura area
Tidal gate: Tidal gates were installed in some places in Minami-Sanriku town similar to otherareas in the Sanriku coast as to protect and reduce tsunami damage. However, all of the tidal
gates in Minami-Sanriku could not help to protect the town. Fig. 7-left shows an example offour gates with 4.5 m height and 11.0 m in total span length. On the other hand, there was oneplace that the gate could fully help to protect the village called Fudai as the number ofcasualty was zero.

4

Tsunami memorial stone: Such as stone monuments, can be found in many areas along theSanriku coast. In Minami-Sanriku town, there are monuments for the 1896 Meiji, the 1933
Showa and the 1960 Chile tsunamis. The message on the stone monument for the 1960 Chiletsunami reads “to be cautious of an abnormal receding wave”. However, these monuments,including a 2.6 m high monument for the 1960 Chile tsunami were destroyed by the 2011
Tohoku tsunami.

Fig. 7 Tsunami gate (3/9/2011) and tsunami memorial stone (3/9/2011)
Disaster prevention building: Similar to other areas officers and staff members that werestationed at the disaster prevention building (Fig. 8-left) in Minami-Sanriku Only 10 peopleof the 130 employee of the town hall (including the Mayor of Minami-Sanriku town weresurvived by reaching the top floor of this building). The remaining damaged building is
considered as one of 37 structures in Miyagi prefecture proposed to be preserved as
memorials of the 2011 event and to maintain tsunami awareness. During the 2011 tsunami,Miki Endo ( 遠藤 未 希 ), a 25 year old employed by the town's Crisis Management
Department sacrificed her life to continue broadcast disaster advisories and warnings over thecommunity loudspeaker system, located in the Crisis Management Department's building, as
the tsunami overwhelmed it.
JR train station: Many train lines and train stations operated by the Japan Railway company(JR) were damaged or destroyed. There are seven main lines, Hachinohe, Yamada, Ofunato,Kesennuma, Ishinomaki, Senseki and Joban line. JR reported that there were 48 stations
damaged or washed away and 99 stations were inspected and repaired. Total damage to thetrain line was 1,780 places covering the total length of 325 km. Shizugawa station (Fig.
8-right) belongs to the Kesennuma line. The station was washed away and the train line wastotally destroyed. Most typical damage to the train is that the train was derailed or overturned.

Fig. 8 Disaster prevention building (3/9/2011) and JR train station (3/9/2011)5

Shizugawa Elementary School: This school was used by tsunami evacuee for several weeks,and in the first week they wrote ‘SOS’ sign in the field to attract the rescue. The school wasan example of a shelter that survived the tsunami. However, there were many example of an
unfortunate result from the unexpected tsunami such as Okawa primary school which locatednear the mouth of the Kitakami River in Ishinomaki city where the tsunami claimed 74 out ofa total of 108 children and 10 staff.
Minami-Sanriku Sun Sun shopping village: The shopping village was opened in Feb 2012using the pre-fabricated structure similar to a typical temporary house for tsunami affected
residents. The area comprises of 30 shops including fresh aqua-agricultural products andvarious kind of restaurant using ingredients from Minami-Sanriku town. There was also someevent took place here to promote the town’s reconstruction.

Fig. 9 Shizugawa Elementary School and shopping village (28/7/2012)
Tsunami inundation sign: Tsunami inundation signs of the 1960 Chile tsunami were put inmany places in the Sanriku coast including the Minami-Sanriku town. Most of the heights of
the 1960 event were lower than 5 m in general, however, greater than 10 m for the 2011 event.
At present, Miyagi prefecture has already prepared and put the inundation sign for the 2011
event in many places such as survived buildings and structures. These signs are very
important to maintain tsunami awareness and recall about tsunami hazard in each tsunami
affected area.

Fig. 10 Tsunami inundation sign (3/9/2011)6

Appendix: Vulnerability of the 2011 tsunami for supporting the reconstruction
Human fatality
The great one in 1896 Meiji-Sanriku tsunami had an average tsunami height greater than 10m with also high fatality ratio. After 37 years from the 1896 event, 1933 Showa-Sanriku had
smaller fatality ratio even they also experienced large tsunami height. The fatality ratio forthe 2011 Tohoku tsunami in Sanriku coast is similar to the 1933 event as they were attacked
by great tsunami but experience may help decreasing the fatality ratio. For the 2011 Tohoku
tsunami in Sendai Plain coast is comparatively smaller in tsunami height but caused
somewhat high fatality ratio. This figure shows importance of experience in reducing humanloss by tsunami.
Fishery boat
Damaged data of fishery boat due to three historical tsunamis in Japan namely, 1896
Meiji-Sanriku, 1933 Showa-Sanriku and 1983 Japan Sea tsunami were available. Ratios ofdamaged or washed away boats were then calculated against reported maximum tsunami
height for each village. Based on the results obtained from the previous three events, it canconcluded that damage is observed in small boat when tsunami height is greater than 2 m andtotally damage when the height is greater than 5 m. However, half of ship is still has lessdamage even the height is greater than 5 m. These results are similar to what we obtained
from the 2011 event. Fishery boats that is larger than 5 tons show higher performance.
< 5t5-20 t

10.8101771 Meiwa
1896 Meiji
1933 Showa
1944 Tonankai
1946 Nankai
1960 Chile
1993 Okushiri
2011 Tohoku Ria
2011 Tohoku Plain

10.1

0.01
110Maximum tsunami height (m)100

Damage ratio

Fatality ratio (%)

100

0.6
0.4
0.2
005101520
Max. tsunami height (m)Fig. 11 Tsunami fatality ratio (2011 and historical events) and fishery boat damage ratio(2011 event) in Japan
Housing and building
Tsunami fragility curves were developed based on data for 63,605 buildings in Ishinomaki
city and can be summarized as below.
- Coastal topography: For a given inundation depth, a higher damage probability exists on theria coast due to higher flow velocity. The characteristic of building damage due to tsunami inthe plain area are similar to those observed due to flooding in Japan.
- Building function: Performance by building function depends primarily on the building
materials. The size and complexity of buildings might also be related to building performance,
given that residential building was found to be the weakest.
- Structural material: It is clear that RC and steel buildings performed better than wood andmasonry buildings.
- Number of stories: Better performance was observed for buildings with three or more
7

stories, followed by buildings with two stories and buildings with one story. The performanceof buildings with three or more stories is particularly significant.
- Construction year: Buildings constructed after 1981 performed slightly better than buildings
constructed between 1971 and 1981. The earthquake-resistant building code in force at thetime of construction has almost no relation to tsunami damage.
LV1: Minor damage(To be used afterminor clean up)
LV2:
Moderate
damage (To be used
aftermoderate
reparation)
LV3: Major damage(To be used after
major reparation)
LV4:
Completedamage (To be usedafter
completereparationandretrofitting)
LV5: Collapsed(Non-repairable)
LV6: Washed away
(Non-repairable)

Fig. 12 Area map of Ishinomaki city and explanation of building damage level

0.80.60.4(a)0.2

Ria all00 2 4 6 8 10 12 14
Inundation depth (m)
LV3

LV4

LV50.80.60.2(b)Plain all00 1 2 3 4 5 6 7 8 9 10Inundation depth (m)

LV3

LV4LV5LV6

1
0.8
0.60.4(c)0.2

Ria (House)

00 2 4 6 8 10 1214
Inundation depth (m)LV2

LV610.4

LV2

LV3

LV4

LV5

0.80.60.2(d)Ria (Public Bld.)

00 2 4 6 8 10 12 14
Inundation depth (m)

LV3

LV4LV5LV61
0.8
0.6
0.4(e)

0.2

Plain (11RC+S)

00 2 4 6 8 10
Inundation depth (m)LV2

LV610.4

LV2

Probability of occurrence

LV6Probability of occurrence

LV51

LV2

Probability of occurrence

LV4

Probability of occurrence

LV3

Probability of occurrence

Probability of occurrence

LV2

LV3

LV4

LV5

LV6

1
0.8
0.6
0.4(f)
0.2

Plain (11W)

00 2 4 6 8 10
Inundation depth (m)Fig. 13 Comparison of tsunami fragility curves for ria (a), plain coast (b), residential house (c), publicbuilding (d), RC or steel house with (e) and wooden house
8Pedestrian bridge
Pedestrian bridges played important role as they saved many people’s lives during the 2011
tsunami and can be used as an emergency tsunami evacuation place in the future. Total of 68
pedestrian bridges including the ones in train station from six prefectures along the East coastof Japan were analyzed. Damage is classified as a) heavily damage (washed away), b)
slightly damage (only stair remained) and c) no damage (inundated only). We found from theresults that the pedestrian bridge will start to be damaged by tsunami if 1) the tsunami flow
depth is higher (1.5 times) than the bridge’s height or 2) if the location of pedestrian bridge
relative from the shoreline is 1/10 of the maximum inundation in land.

No Prefecture P. Bridge T. Bridge Total
1 Hokkaido
4042 Aomori
0113 Iwate
112
134 Miyagi
22830
5 Fukushima 102126 Ibaraki
088Total
68Fig. 14 Damage to pedestrian bridge and their damage classification

Fig. 15 Fragility curves of pedestrain bridge shown against the ratio of tsunami flow depth (h)over the bridge’s height and distance from shoreline to the bridge (l) over the maximum
inundation distance (L)9References
Abe, I. and Imamura, F. (2010), “The 3rd International Tsunami Field Symposium (ITFS),
Sanriku field trip guidebook”, 2010, 11 p.
Japan Meteorological Agency (JMA) (2011) “The 2011 off the Pacific coast of Tohoku
earthquake”, http://www.jma.go.jp/jma/en/2011_Earthquake.html (accessed 12 June 2011)
Muhari, A., Imamura, F. and Koshimura F. (2012) Performance evaluation of pedestrian
bridge as vertical evacuation site during the 2011 tsunami in Japan, Journal of NaturalDisaster Science, 34 (1), 79-90.
Suppasri, A., Muhari, A., Ranasinghe, P., Mas, E., Shuto, N., Imamura, F. and Koshimura, S.
(2012) Damage and reconstruction after the 2004 Indian Ocean tsunami and the 2011
Great East Japan tsunami, Journal of Natural Disaster Science, 34 (1), 19-39.
Suppasri, A., Imai, K. and Imamura, F., Developing fragility curves based on surveyed dataof the 2011 Great East Japan tsunami in Ishinomaki city, Natural Hazards and EarthSystem Sciences (in revision)
Suppasri, A., Shuto, N., Imamura, F., Koshimura, S., Mas, E. and Yalciner, A.C., Lessons
learned from the 2011 Great East Japan tsunami: Performance of tsunami countermeasures,coastal buildings and tsunami evacuation in Japan, Pure and Applied Geophysics(published online)
Yamashita, F. (2008), Tsunami and disaster prevention-Sanriku tsunami, Kokon-Shoinpublishing, 158 p, ISBN-13: 978-4772241175

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