TRACE SURVEY OF THE 2011 TOHOKU TSUNAMI IN THE NORTH OF MIYAGI PREFECTURE AND NUMERICAL SIMULATION OF BIDIRECTIONAL TSUNAMIS IN UTATSUSAKI PENINSULA

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1 Coastal Engineering Journal, Vol. 54, No. 1 (2012) (28 pages) c World Scientific Publishing Company and Japan Society of Civil Engineers DOI: /S TRACE SURVEY OF THE 2011 TOHOKU TSUNAMI IN THE NORTH OF MIYAGI PREFECTURE AND NUMERICAL SIMULATION OF BIDIRECTIONAL TSUNAMIS IN UTATSUSAKI PENINSULA TARO KAKINUMA Graduate School of Science and Engineering, Kagoshima University, Korimoto, Kagoshima, Kagoshima , Japan taro@oce.kagoshima-u.ac.jp GOZO TSUJIMOTO Department of Urban Engineering, Kobe City College of Technology, 8-3 Gakuenhigashi-cho, Nishi-ku, Kobe, Hyogo , Japan tujimoto@kobe-kosen.ac.jp TOMOHIRO YASUDA Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto , Japan yasuda.tomohiro.4x@kyoto-u.ac.jp TAKASHI TAMADA Coastal Operation Division, Idea Consultants, Inc., Hayabuchi, Tsuzuki-ku, Yokohama, Kanagawa , Japan tamada@ideacon.co.jp Received 7 November 2011 Accepted 13 January 2012 Published 24 March 2012 The field survey results obtained by the team of authors in the north of Miyagi Prefecture between April 1 and 6, 2011 are summarized referring to a part of the survey results by other teams of the 2011 Tohoku Earthquake Tsunami Joint Survey Group. The inundation height above sea level was measured using a laser range finder with a reflection prism. The inundation height was generally larger at bay heads, as well as promontory tips, except

2 T. Kakinuma et al. several points, which were sheltered by a peninsula or had a tapering area. The tsunamis reached inland far away from the sea along valleys and rivers. Not only steel frame buildings but also many reinforced concrete buildings were collapsed in Onagawa Town. According to the numerical results, the first of tsunamis from the west coast and the second of tsunamis from the east coast should come together in Utatsusaki Peninsula, which is consistent with the interviews to survivors. Keywords: Tsunami; post event survey; inundation height; bidirectional tsunamis. 1. Introduction At 14:46 JST, March 11, 2011, a mega earthquake occurred off the Pacific coast of the Tohoku region, Japan, causing enormous tsunamis which devastated the coastal areas in the northeast of Japan. The moment magnitude of the earthquake was 9.0, which was the 4th largest earthquake ever recorded. Miyagi Prefecture in the Tohoku region was one of the most damaged areas due to the tsunamis since the epicenter was located off the Oshika Peninsula in the prefecture. In the present paper, the results of field survey conducted by the team of authors between April 1 and 6, 2011, as part of the 2011 Tohoku Earthquake Tsunami Joint Survey Group (JSG), are summarized including the inundation height of tsunamis, as well as the extent of damage, in the north of Miyagi Prefecture in reference to the survey results obtained by other teams of JSG, although the disaster was too heavy to be covered all. Figure 1 shows the administrative districts of Miyagi Prefecture. The coastline configuration of the prefecture can be divided into two parts: an undulating area of ria coasts from Kesennuma City to Oshika Peninsula and a plain area of even coastlines from the west of Ishinomaki City to Yamamoto Town. A part of the trace survey results of inundation height [Mori et al., 2012] in Miyagi Prefecture is shown in Fig. 2. In the present paper, the inundation height is determined as the maximum level of water surface when the water surface is estimated not to have reached the maximum level quite locally and instantaneously but to have been kept at the level for a while; the unit of inundation height is meter over Tokyo Peil (T.P.), i.e. the standard mean sea level in Tokyo Bay. According to Fig. 2, the inundation height was generally larger in the north of Miyagi due to the deeply indented, i.e. saw-tooth coastlines, where the tsunamis should be concentrated at bay heads, as well as promontory tips, than in the south of the prefecture. First, the field survey results of inundation height in the north of Miyagi Prefecture, i.e. Kesennuma City, Minamisanriku Town, Onagawa Town, and the east coast of Ishinomaki City, are described in this paper. The team of authors used a laser range finder Impulse 200 with a reflection prism to obtain inundation height above sea level during the survey, after that the inundation height was changed to that in T.P. meters. The values of latitude and longitude were measured using a GPS receiver. The survey results are mentioned from north to south. Several toppled reinforced concrete buildings in Onagawa Town are also introduced. Second, a numerical analysis is conducted to study local circumstances of tsunamis attacking Utatsusaki Peninsula, where bidirectional tsunamis should propagate from both the east and

3 Trace Survey of the 2011 Tohoku Tsunami in the North of Miyagi Prefecture Fig. 1. Administrative districts of Miyagi Prefecture. west coasts of the peninsula to come together according to eyewitness accounts. The numerical simulation has been performed using nonlinear shallow water equations, which were solved through a finite difference method. 2. Field Survey Results 2.1. Kesennuma City Kesennuma Port Around Kesennuma Port, although the low-ground area was damaged, the inundation height showed rather low level between 3 m and 9 m, which are indicated by plots circled with Ellipse P 1 in Fig. 2, because the port was behind the Karakuwa Peninsula as shown in Fig. 1. Figure 3 shows a fishing boat with a car, which ran into a house near a port wharf

4 T. Kakinuma et al. Fig. 2. Distribution of inundation height in Miyagi Prefecture (The north latitude in the right-hand side graph corresponds to that in the left-hand side map. The data include a part of the trace survey results obtained by other teams of JSG [Mori et al., 2012]). Fig. 3. Fishing boat stranded on a road facing Kesennuma Port (The photo was taken on April 2, 2011)

5 Trace Survey of the 2011 Tohoku Tsunami in the North of Miyagi Prefecture Hajikamimukaibara The distribution of inundation height in both the south of Kesennuma City and Minamisanriku Town is shown in Fig. 4. The inundation height was generally larger at bay heads due to concentration of the tsunami energy, as well as promontory tips through refraction of tsunami waves. The area Q 1 in Fig. 4 is enlarged in Fig. 5, where on house walls at Point 1, i.e. exactly at the center of the circle surrounding the character 1, in Hajikamimukaibara facing Oisehama Beach, tsunami trace lines were marked clearly at the level 16.0 m above sea level. Figure 6 shows houses around Point 1 : the second Fig. 4. Distribution of inundation height measured by the authors in both the south of Kesennuma City and Minamisanriku Town (unit: m)

6 T. Kakinuma et al. Fig. 5. Hajikamimukaibara ( 1 :N , E )andmishima(2 :N , E ). Fig. 6. Damaged houses in Hajikamimukaibara on April 2, 2011 (The left-hand side house was collided with the second floor of the right-hand side house)

7 Trace Survey of the 2011 Tohoku Tsunami in the North of Miyagi Prefecture floor of the right-hand side house was swept for a horizontal distance of approximately 50 m to come into collision with the left-hand side house, the foundation level of which was higher than that of the swept house by 2 m or 3 m. Point 1 is around 400 m away from the coastline as the crow flies, where the distance from a coastline is described as the direct distance between the place and the coast nearest to it in the present paper Motoyoshi Town (1) Mishima On walls of a house at Point 2, which was around 240 m away from the coast, in Mishima facing Ooyakaigan Coast in Fig. 5, there were clear trace lines at the level 15.1 m above sea level. It was confirmed that the houses on foundations at the level higher than that of the present house by more than 0.5 m were not damaged. The sandy beaches of both Oisehama Beach and Ooyakaigan Coast seem to have lost sand zones around 50 m wide in the cross-shore direction by comparing before with after the tsunami event possibly due to subsidence of ground or erosion by tsunamis; the satellite photographs of Oisehama Beach before and after the tsunami attack are shown in Fig. 7. (2) Akaushi The area Q 2 in Fig. 4 is magnified in Fig. 8. Inside the hall of Atago Shrine at Point 1 in Fig. 8, there were distinct trace lines at the level 23.0 m above sea level, where Atago Shrine was on a hill as shown in Fig. 9, around 180 m away from the shoreline. Fig. 7. Satellite photographs of Oisehama Beach before and after the tsunami attack ( c 2010 Google, c 2011 Cnes/Spot Image, Image c 2011 TerraMetrics)

8 T. Kakinuma et al. Fig. 8. Akaushi ( 1 : N , E ) and Koganezawa ( 2 : N , E ). Fig. 9. Atago Shrine in Akaushi on April 5,

9 Trace Survey of the 2011 Tohoku Tsunami in the North of Miyagi Prefecture (3) Koganezawa On doors and walls of a house at Point 2 in Fig. 8, trace lines were plainly drawn at the level 19.1 m above sea level behind Koganezawa Station on Kesennuma Line of East Japan Railway Company, around 100 m away from the shore. The horizontal distance between Atago Shrine and Koganezawa Station was less than 400 m; nevertheless the difference in inundation height between them is significant, i.e. 3.9 m. Atago Shrine was located on a hill in a tapering area and the tsunamis should become higher through run-up or reflection on the hill cliff. (4) Utou The area Q 3 in Fig. 4 is expanded in Fig. 10, where on walls and windows of a house at Point 1 in Utou, clear trace lines were remained at the level 19.3 m above sea level and around 200 m away from the shoreline. Kurauchi Fishing Port was protected by breakwaters against wind waves but the breakwater height was too low to hinder the higher and longer tsunamis from propagating towards the land. Fig. 10. Utou ( 1 :N , E )

10 T. Kakinuma et al. Fig. 11. Utatsu Natari ( 1 :N , E ; 2 :N , E ) Minamisanriku Town Utatsu area (1) Utatsu Natari The area Q 4 in Fig. 4 is enlarged in Fig. 11. A sign board showing the inundation level was put on a private-house fence at Point 1 in Fig. 11 by an inhabitant of the house on the east of Natari Elementary School. The top edge of the plate was at the level 17.7 m above sea level and around 170 m away from the coast. After the attack of the 1933 Showa Sanriku Tsunami, he and his neighbors had moved out their low-ground residential areas on the map of Fig. 11 to higher hills, where they must cut down tall cedars, such that his house was only flooded just above floor level without breakage. On a door and walls of a pet house of Natari Elementary School at Point 2 in Fig. 11, distinct trace lines were drawn at the level 17.8 m above sea level and around 200 m away from the shore. The athletic field, which was at the same level as the foundation of the school buildings and lower than that of the pet house, was designated as an evacuation site for the local residents against tsunamis but the level is about 6 m lower than the actual inundation height. (2) Utatsu Baba The area Q 5 in Fig. 4 is magnified in Fig. 12, including the area shown in Fig. 11. The inundation height at Point 1 in Fig. 12 was just over the plum trees on a cliff slope

11 Trace Survey of the 2011 Tohoku Tsunami in the North of Miyagi Prefecture Fig. 12. Utatsu Baba ( 1 :N , E )andutatsuooiso(2 :N , E ). according to survivors and the inundation level, where there was a lot of debris, was 15.7 m above sea level, around 290 m away from the coastline. The affected family, whose house has been washed away, never imagined that the tsunamis would reach their house when they were staying out of doors at the level of the house foundation more than 10 m higher than the local mean sea level and listening to the tsunami warning through a community broadcast, which said that Japan Meteorological Agency forecasted the tsunami height to be 6 m. Although the predicted tsunami

12 T. Kakinuma et al. Fig. 13. Panoramic view in Utatsusaki Peninsula on April 5, height was changed to 10 m before the tsunami run-up, the family could not get the updated information because of the crash of the community wireless system. They, however, watched the tsunamis approaching to themselves and then were sure that the tsunamis must be higher than estimated, after that they quickly climbed the hill to the rear of their house. On the hill they heard the breaking sound like burry burry in the tsunamis and looked at the flat water surface from below to offshore for around 20 min. Their house was lost in the tsunamis even though their ancestors had moved to the higher place after the 1896 Meiji Sanriku Tsunami. The family was friendly through our interview and looked energetic to blaze a new path to the future, such that the authors were impressed and felt sad in the car leaving them. The family also observed that in some distance the water surface rose roughly 4 m higher than the water surface below; the place is indicated by a dashed circle in Fig. 12. From this place, a panoramic photo, i.e. Fig. 13, was taken to show both the east and west sides of Utatsusaki Peninsula. Several survivors told that bidirectional tsunamis came together from both the east and west coasts of the peninsula, which will be examined through numerical computation in Sec. 3. (3) Utatsu Ooiso In front of a house at Point 2 in Fig. 12, an inhabitant pointed out the inundation height, which was confirmed through debris, at the level 13.3 m above sea level and around 270 m away from the coastline Shizugawa area (1) Shizugawa Komori The flooded area in Shizugawa has been in ruins remaining only several reinforced concrete buildings including Shizugawa Public Hospital as shown in Fig. 14, where steel frame buildings revealed their fragility. The distribution of inundation height around Shizugawa Bay is shown in Fig. 15. Especially along rivers, the tsunamis mercilessly reached inland far away from the sea: at Point 1 in Fig. 15, a lot of debris was left at the foot of a hill along Route 398, which paralleled a river, and the

13 Trace Survey of the 2011 Tohoku Tsunami in the North of Miyagi Prefecture Fig. 14. View of Shizugawa on April 5, Fig. 15. Distribution of inundation height around Shizugawa Bay ( 1 : N , E )

14 T. Kakinuma et al. Fig. 16. Tsunami traces on the building of Shizuhama Station on April 3, Fig. 17. Shizugawa Oda ( 1 :N , E ), Shizugawa Hiraiso ( 2 :N , E ), and Shizugawa Oomori ( 3 :N , E )

15 Trace Survey of the 2011 Tohoku Tsunami in the North of Miyagi Prefecture level was roughly 18 m above sea level through a GPS receiver and around 2.5 km away from the coast. (2) Shizugawa Oda There were trace lines remained clearly on walls of Shizuhama Station on Kesennuma Line as shown in Fig. 16. The area Q 6 in Fig. 4 is expanded in Fig. 17, at Point 1 of which the trace lines of the station were at the level 12.1 m above sea level and around 260 m away from the shore. The tsunami height was over the level of railways, such that Kesennuma Line was heavily damaged: its railway concrete bridges were fallen as shown in Fig. 18 possibly due to not only horizontal but also upward force. Iron rails could not be cut easily, resulting in their bending or falling as shown in Fig. 19. Fig. 18. Railway concrete bridges of Kesennuma Line on April 5, 2011, where no bridge girder is found inside the ellipses drawn on the photo. Fig. 19. Bended and fallen rail track of Kesennuma Line on April 3,

16 T. Kakinuma et al. A large collision trace, which was evidenced not to have been there before the tsunami attack, was remained on the roof of Shizuhama Station as shown in Fig. 16 at the level about 2 m higher than the above-mentioned trace lines on walls, which means that damages can be developed at the level of several meters above inundation height due to some floating objects or splashes. (3) Shizugawa Hiraiso On windows of the second floor of a house at Point 2 in Fig. 17, trace lines were marked plainly at the level 13.3 m above sea level and around 50 m away from the coastline. (4) Shizugawa Oomori On live trees or hill slopes at Point 3 in Fig. 17, a wooden door and many other things were left at the level 12.1 m above sea level and around 120 m away from the shoreline Togura area (1) Togura The area Q 7 in Fig. 4 is enlarged in Fig. 20, where on windows of a house located on a hill at Point 1 in Togura, clear trace lines were remained at the level 20.5 m above sea level and around 450 m away from the coast. According to an interview to a person who was carried by the tsunami flow for approximately 300 m off Togura, many persons had such experiences: another person who promptly rode on a roof of a floating house to take refuge was flown offshore until he was rescued by a fishing boat in the night of that day. Trace lines were distinctly drawn on the ground-floor windows of Togura Junior High School at Point 2 in Fig. 20 or 21, where the inundation height was at the level 20.0 m and around 70 m away from the shoreline. Togura Junior High School was located on a hill, at the foot of which moai statues were built to the memory of the 1960 Chilean Earthquake Tsunami as shown in the right-hand side photo of Fig. 21, such that the maximum inundation depth at the school was only 1.7 m, while Togura Elementary School stood at Point 3 inside the low-lying area as shown in the contour map of Fig. 20 or 21, which resulted in oyster shells left on the rooftop of the three-storied building of Togura Elementary School due to the tsunamis. It should be noted that coastal parapets were left near Point 3 in Fig. 20, which means that they were flown for around 100 m from the coastline. Along the Oritate River, the inundation height showed a large value even inland, i.e m above sea level at Point 4 in the map of Fig. 21 around 2 km away from the river mouth

17 Trace Survey of the 2011 Tohoku Tsunami in the North of Miyagi Prefecture Fig. 20. Togura ( 1 :N , E ; 2 :N , E ). Fig. 21. Two schools in Togura (The photos were taken on April 3, Points 2 and 3 are the same places as those in Fig. 20 in that order. The unit of inundation height in the map is meter)

18 T. Kakinuma et al. Fig. 22. Cape Kamiwari-zaki ( 1 :N , E ) and Juusanhama Oozashi ( 2 : N , E ). (2) Cape Kamiwari-zaki The area Q 8 in Fig. 4 is magnified in Fig. 22. Traces including debris and discolored grasses on a road-side slope were remained at Point 1 in Fig. 22, where they were left at the level 15.5 m above sea level and around 60 m away from the coast

19 Trace Survey of the 2011 Tohoku Tsunami in the North of Miyagi Prefecture Fig. 23. View of Juusanhama Oozashi on April 3, East of Ishinomaki City Juusanhama Oozashi, Kitakami Town The tsunami height was generally higher in the east than in the west of Oshika Peninsula as shown in Fig. 2 and various values of inundation height appeared in the east of Ishinomaki City. According to interviews to local people, as well as referring to a lot of debris on a hill slope, the inundation height at Point 2 in Fig. 22 was 17.2 m above sea level, where the site was around 220 m away from the shore. Figure 23 shows house foundations in front of a damaged marine-product factory. In the present area, everyone survived on the nearby hill owing to the tsunami warning through a community broadcast since they had been ready to take refuge after the experience of inundation due to the 1933 Showa Sanriku Tsunami Yagawahama Quite a large value of inundation height was obtained by JSG in Yagawahama facing Sameura Bay, where the bay is indicated in Fig. 1 and the plot is surrounded by Circle P 4 in Fig. 2. The inundation height was 25.8 m at Point 1 along the Ya River indicated in Fig. 24, where Ya of the name means a valley in Japanese Onagawa Town Onagawa Port The inundation height was high through the coast around Onagawa Bay as shown by the plots circled with Ellipse P 3 in Fig. 2, such that Onagawa Town was one of the most damaged places due to the tsunamis. The distribution of inundation height

20 T. Kakinuma et al. Fig. 24. Yagawahama (The area around Point 1 in the left-hand side map is expanded in the right-hand side one, where Point 1 shows the same site in these two maps. The unit of inundation height is meter). Fig. 25. Distribution of inundation height in Onagawa Town (The unit of inundation height is meter). in the town is shown in Fig. 25. The Onagawa Town Hospital located at the center of Circle A shown in Fig. 25 was built on a hill top at the level about 16 m above sea level, such that only the ground floor was inundated by the tsunamis, where the maximum inundation depth was 2.0 m

21 Trace Survey of the 2011 Tohoku Tsunami in the North of Miyagi Prefecture Fig. 26. Example of damaged reinforced concrete buildings in Onagawa Town, where Building A is toppled down not behind Building C, i.e. the north wing of Marinpal Onagawa (The photo was taken on September 21, 2011). Fig. 27. Foundation bottom of Building A in Fig. 26 (The photo was taken on April 26, 2011) Collapse of reinforced concrete buildings One of the significant features of damage in Onagawa Town was collapse of many reinforced concrete buildings, which are mentioned also in Suppasri et al. [2012] and Mikami et al. [2012]. An example is shown in Figs. 26 and 27: Building A was toppled and carried as shown in Fig. 26 and the bottom of its foundation was revealed as shown in Fig. 27 with foundation piles pulled out. The Buildings A, B, and C are in Circle B on the map of Fig. 25. The reason why Building B behind Building C, i.e. the north wing of Marinpal Onagawa, which was a facility for sightseeing and shopping,

22 T. Kakinuma et al. survived is not clear without information on conditions of structure, foundation, etc. but such a robust building as Building C is expected to play a role of a barrier to reduce tsunami force and current. It should be noted, however, that large velocity can be developed in a narrow space between strong structures as a big tsunami passes, resulting in, for example, local scouring between the north and south wings of Marinpal Onagawa as shown in Fig. 28. Fig. 28. Local scouring between two wings of Marinpal Onagawa (The photo was taken on April 26, 2011). Fig. 29. Examples of reinforced concrete buildings collapsed in Onagawa Town (The photos were taken on April 26, 2011)

23 Trace Survey of the 2011 Tohoku Tsunami in the North of Miyagi Prefecture Other examples of reinforced concrete buildings collapsed in Onagawa Town are introduced in Fig. 29. Reinforced concrete buildings are often used as shelters; in fact the south wing of Marinpal Onagawa was designated as an evacuation building against tsunamis but the huge tsunamis propagated over it. Future work is required to elucidate the mechanism of fall or collapse of structures due to seismic oscillation, soil liquefaction, force of repeating water current, sand motion, and aging of the structure. 3. Numerical Simulation of Bidirectional Tsunamis Over a Peninsula Several survivors observed tsunamis coming together from both the east and west coasts of Utatsusaki Peninsula as mentioned in (2). The bidirectional-tsunami propagation over the peninsula has been simulated through a numerical model based on nonlinear shallow water equations, which are used also in Mori et al. [2012], Watanabe et al. [2012], and Shimozono et al. [2012] in this special issue. The computation domain is shown in Fig. 30, where 4 domains of different mesh resolution, i.e m, 450 m, 150 m, and 50 m, are nested in that order. The initial profile of water surface over dislocation is assumed to be the same as the permanent shift of seabed calculated through the method of Mansinha and Smylie [1971] using the fault model presented by Tohoku University [Imamura et al., 2011]. The fault is divided into 10 segments as shown in Fig. 31, where the length, width, strike, dip, and rake of all the segments are 100 km, 100 km, 193,14,and81, respectively, while other parameters are listed in Table 1. The bottom friction is treated by choosing Manning s roughness between m 1/3 s and 0.04 m 1/3 s considering land use. The dry and wet model by Iwasaki and Mano [1979] is utilized to simulate tsunami run-up. The time development is carried out using the leap-frog finite difference scheme with the staggered Arawaka C-grid [Arakawa and Lamb, 1977]. The time interval t is equal to 0.5 s satisfying the Courant-Friedrichs-Lewy Condition. Table 1. Parameters of the fault model [Imamura et al., 2011]. No. Latitude ( N) Longitude ( E) Slip (m) Depth (km)

24 T. Kakinuma et al. Fig. 30. Computational domain, which consists of 4 domains of different mesh intervals. Fig. 31. Segments of the fault model [Imamura et al., 2011]

25 Trace Survey of the 2011 Tohoku Tsunami in the North of Miyagi Prefecture The calculation result of water surface displacement at the position of North Miyagi GPS Buoy is shown in Fig. 32 in comparison with the observed data through the GPS buoy [Kawai et al., 2011], where the buoy was located at the point (N , E ) and the water depth was about 160 m. Calculation Fig. 32. Numerical result of water surface displacement at the position of North Miyagi GPS Buoy in comparison with the observed data through the GPS buoy [Kawai et al., 2011]. Fig. 33. Altitude in a part of Utatsusaki Peninsula (Points 1 and 2 are the same places as those in Fig. 12 in that order)

26 T. Kakinuma et al. Fig. 34. Numerical result of time variation in water level at each point indicated in Fig. 33. results of time variation in water level at Points 1 10 in Fig. 33 are shown in Fig. 34, according to which the maximum inundation depth is larger than 10 m at Points 1, 2, 3, 6, 8, 9, and 10. The first peak reaches the east coast of the peninsula and passes over Points 1 6, after that the inundation depth is 1.7 m at Point 7, where no tsunami has come yet from the west coast. About 7 min later than the first peak appeared at Point 1, Points 8 10 on the west coast are attacked by the tsunami coming from the west or south, while the second peak appears at the east coast and travels towards the southwest. Then the first tsunami from the west coast and the second tsunami from the east coast come together around Point 3 or 4, which is consistent with the interviews, although the calculation results depend on the fault model. The distribution of the maximum calculated inundation height in the

27 Trace Survey of the 2011 Tohoku Tsunami in the North of Miyagi Prefecture Fig. 35. Numerical result of the maximum inundation height in the area shown in Fig. 33. area of Fig. 33 during the tsunami event is shown in Fig. 35, where the maximum inundation height is between 13 m and 20 m in the area and higher on the east than on the west of the watershed of peninsula, which agrees with the field survey results referring to the interviews to survivors. 4. Conclusions The field survey results obtained in the north of Miyagi Prefecture were summarized referring to a part of the survey results by other teams of JSG. The inundation height in both Kesennuma City and Minamisanriku Town was generally larger at bay heads and promontory tips except several points including both the Kesennuma Port area sheltered by Karakuwa Peninsula and Akaushi having a tapering area. The first of tsunamis from the west coast and the second of tsunamis from the east coast should come together in Utatsusaki Peninsula according to the numerical simulation, which is consistent with the interviews to survivors. The steel frame buildings revealed their fragility around Shizugawa Bay, where the tsunamis reached inland far away from the sea along valleys and rivers. The inundation height was generally higher in the east than in the west of Oshika Peninsula in the east of Ishinomaki City. It should be noted that many reinforced concrete buildings were collapsed in Onagawa Town. It is both syntheses of general damage and analyses of local characteristics that are important to achieve community reconstruction

28 T. Kakinuma et al. Acknowledgments The authors are deeply grateful to the local people in the affected areas who gave us precious reports about the disaster. The survey of the authors could not be carried out without the support of instrument arrangement etc. by Prof. T. Hosoyamada, Nagaoka University of Technology. Sincere gratitude is extended to Prof. S. Sato, the University of Tokyo, who is the editor of the paper, and the reviewers for their meaningful comments. References Arakawa, A. & Lamb, V. R. [1977] Computational design of the basic dynamical processes of the UCLA general circulation model, Meth. Comput. Phys. 17, Imamura, F., Koshimura, S., Ooya, R., Mabuchi, Y. & Murashima, Y. [2011] Tohoku University model (version 1.0), tohoku 2011/model/, 1 12 (in Japanese). Iwasaki, T. & Mano, A. [1979] Numerical simulation of two-dimensional tsunami runup by Euler s coordinates, Proc. 26th Japanese Conf. Coastal Eng., pp (in Japanese). Kawai, H., Satoh, M., Kawaguchi, K. & Seki, K. [2011] Characteristics of the 2011 off the Pacific Coast of Tohoku Earthquake Tsunami, Rep. Port Airport Res. Inst. 50(4), 3 63 (in Japanese). Mansinha, L. & Smylie, D. E. [1971] The displacement fields of inclined faults, Bull. Seismol. Soc. Am. 61, Mikami, T., Shibayama, T., Esteban, M. & Matsumaru, R. [2012] Field survey of the 2011 Tohoku Earthquake and Tsunami in Miyagi and Fukushima Prefectures, Coast. Eng. J. 54(1), Mori, N., Takahashi, T. & The 2011 Tohoku Earthquake Tsunami Joint Survey Group [2012] Nationwide post event survey and analysis of the 2011 Tohoku Earthquake Tsunami, Coast. Eng. J. 54(1), Shimozono, T., Sato, S., Okayasu, A., Tajima, Y., Fritz, H. M., Liu, H. & Takatawa, T. [2012] Propagation and inundation characteristics of the 2011 Tohoku Tsunami on the Central Sanriku Coast, Coast. Eng. J. 54(1), Suppasri, A., Koshimura, S., Imai, K., Mas, E., Gokon, H., Muhari, A. & Imamura, F. [2012] Field survey and damage characteristic of the 2011 East Japan Tsunami in Miyagi Prefecture, Coast. Eng. J. 54(1), Watanabe, Y., Mitobe, Y., Saruwatari, A., Yamada, T. & Niida, Y. [2012] Evolution of the 2011 Tohoku Earthquake Tsunami on the Pacific Coast of Hokkaido, Coast. Eng. J. 54(1),