Panon Latcharote

Improvement of Tsunami Countermeasures Based on Lessons from The 2011 Great East Japan Earthquake and Tsunami — Situation After Five Years

The 2011 Great East Japan Tsunami exposed many hidden weaknesses in Japans tsunami countermeasures. Since then, many improvements have been made in both structural measures (numerical simulations, coastal defense structures, building damage assessment and control forests) and nonstructural measures (warning/observation and evacuation). This review summarizes the lessons and improvements in the five-year time period after the 2011 event. After five years, most of the lessons from the 2011 tsunami have been applied, including more realistic tsunami simulations using very fine grids, methods to strengthen coastal defense structures, building evacuations and coastal forests, improved warning content and key points to improve evacuation measures. Nevertheless, large future challenges remain, such as an advanced simulation technique and system for real-time hazard and risk prediction, implementation of coastal defense structures/multilayer countermeasures and encouraging evacuation. In addition, among papers presented at the coastal engineering conference in Japan, the proportion of tsunami-related research in Japan increased from 15% to 35% because of the 2011 tsunami, and approximately 65–70% of tsunami-related studies involve numerical simulation, coastal structures and building damage. These results show the impact of the 2011 tsunami on coastal engineering related to academic institutions and consulting industries in Japan as well as the interest in each tsunami countermeasure.

Possible Failure Mechanism of Buildings Overturned during the 2011 Great East Japan Tsunami in the Town of Onagawa

Six buildings were overturned in the town of Onagawa during the 2011 Great East Japan tsunami. This study investigates the possible failure mechanisms of building overturning during tsunami flow. The tsunami inundation depth and flow velocity at each overturned building were recalculated by using a tsunami numerical simulation and verified using a recorded video. The overturning moment is a result of hydrodynamic and buoyancy forces, whereas the resisting moment is a result of building self-weight and pile resistance force. This study aimed to demonstrate that the building foundation design is critical for preventing buildings from overturning. The analysis results suggest that buoyancy force can generate a larger overturning moment than hydrodynamic force and the failure of a pile foundation could occur during both ground shaking and tsunami flow. For the pile foundation, pile resistance force plays a significant role due to both tension and shear capacities at the pile head and skin friction capacity between the pile and soil, which can be calculated from 18 soil boring data in Onagawa using a conventional method in the AIJ standards. In addition, soil liquefaction can reduce skin friction capacity between the pile and soil resulting in a decrease of the resisting moment from pile resistance force.

Building Damage Assessment and Implications for Future Tsunami Fragility Estimations

Abstract This chapter summarizes perspectives on building damage assessment and their implication for future fragility estimations using damage data from recent tsunamis, including the 2011 event in Japan. Causes of building damage, i.e., a combination of hydrostatic and hydrodynamic forces, debris impact and foundation effects, are explained. Damage scales used in previous studies are introduced, including the scale used for the 2011 tsunami, and possible future damage to be considered in the construction of tsunami evacuation shelters is discussed. Fragility estimations methods are presented, including the PTVA/BTV methods and fragility functions. Fragility functions provide superior, quantitative information compared to other tools, and are thus discussed in depth, from statistical considerations (differences between each model, including the traditional liner models and the new generalized linear models), to the factors affecting the structural performance of buildings. These factors include the type of construction material and the buildings height, function and surroundings. Future improvements and applications of fragility functions considering model diagnostics, additional tsunami parameters, additional building characteristics, and damage scale improvements are also considered. In this sense, research on fragility functions that cover both the preceding earthquake induced damage and the subsequent damage by tsunami represents a challenging future research topic.

DOUBLE-LAYER PLATFORM OF HIGH PERFORMANCE COMPUTING FOR DAMAGE PREDICTION OF RC BUILDINGS SUBJECT TO EARTHQUAKE AND SUBSEQUENT TSUNAMI IN A TARGET AREA

Abstract. For tsunami scenarios, evaluation of tsunami load acting each building depends on surrounding circumstance. Therefore, modeling of all buildings in a target area is important for damage prediction from earthquake and subsequent tsunami. In this study, sequential earthquake and tsunami simulation was developed to predict structural damage from earthquake and subsequent tsunami by means of the application in Integrated Earthquake Simulation (IES). Since IES can simulate only earthquake scenarios with bean-column frame models, IES was modified for input tsunami load acting on a proposed wall-frame model in order to simulate tsunami scenarios using predicted data of tsunami inundation depth. A target area in Kochi city was selected to simulate an earthquake and tsunami scenario because this area has many public buildings and is important for economic activities. A double-layer platform of high performance computing was proposed to simulate this earthquake and tsunami scenario with parallel processing on CPUs and GPUs. The results of sequential earthquake and tsunami simulation show that three-story RC buildings had a significant risk that maximum drift ratio could occur during sequential tsunami response. However, maximum drift ratio from sequential tsunami response was still less than 0.3% in which structural damage didn’t occur obviously. For the worst case scenario that tsunami inundation depth was double, structural damage from sequential tsunami response was much more serious than that of the normalcase scenario in which maximum drift ratio was less than 5% for a four-story RC building. In addition, it was found that low-rise buildings (threeto seven-story) had a significant risk that maximum drift ratio was higher than 1% during sequential tsunami response. The results of sequential earthquake and tsunami simulation can be used to construct further prevention measures.